Bat Conservation Trust 605 4GB, MDR-2, H4, TS400, Micro BR, Zoom H2, Micro Track 24/96, Edirol R-09, Marantz PMD661, Tascam DR-05, Zen V Plus, iFP 700 and 800 series, iFP T30, x20 4GB, X5, D2 16 GB, 8Gb and 4GB, Gmini 400, 500, Duet, D240x, SD1, D1000x, Griffin Guide
Below you will find brief information for MDR-2, Micro BR, Zoom H2, Micro Track 24/96, H4 , Edirol R-09, Marantz PMD661, Tascam DR-05, TS400, Zen V Plus, iFP 700 and 800 series, iFP T30, 605 4GB, x20 4GB, X5, D2 16 GB, 8Gb and 4GB, Gmini 400, Gmini 500, Duet, D240x, SD1, D1000x, Griffin, Anabat SD1, Pettersson D1000x, BatBox Griffin. This document provides guidance on choosing a digital recorder for bat workers. It covers topics like digital sound formats, compression issues, choosing a recorder, sample rate, and quality, and specific models from different manufacturers. If you are looking to purchase a digital recorder for bat work, it is essential to consider the sample rate (ideally 32kHz or 44.1kHz) and quality of the recording. It also discusses the pros and cons of different types of recorders, such as MP3 recorders, solid-state recorders, and minidisks.
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Digital Recording with Bat Detectors Contents: Introduction and Purpose of This Article Digital Sound Formats: A Summary Digital Sound Compression Potential Problems with Compression Choosing a Digital Recorder Capacity of recorders and cards Recorder type Sample rate and quality MP3 Recorders Choosing an mp3 Model Current flash mp3 recorders Hard drive mp3 recorders Solid State Digital Recorders (WAV) Hi MD Digital Voice Recorders Acknowledgements Further Info on the Web Page 1 2 2 4 8 8 9 10 10 11 12 12 13 18 18 19 19 Introduction and Purpose of This Article The array of recorders out there is bordering on the bewildering for the person looking for an external machine to record bat detector output. This is not really a comparative review of specific models as it is extremely difficult to do a meaningful review using controlled tests and also to keep it current, but it will offer some advice and guidelines on choosing a particular type of recorder and what the available options mean for bat workers. Models change all the time and we have not had the resources at BCT to buy a huge range of digital recorders and test them against each other, hence this is a general guideline and we really need more input from those of you using specific models in the field to tell us what you like/don‟t like and what works or doesn‟t work very well about your recorder. We will add in useful comments such as how easy it is to use in the field etc. I have tried to make this relevant to bat workers. If you have any specific comments, corrections or useful information on your experiences in the field with current recorder models, manufacturers, retailers or software compatibility issues please do send them in for inclusion in future versions of this article. If you come across useful information on how the different formats, codecs or technology work etc please just send the link to the web site location or a reference rather than a lot of text. It became clear to me when I began this that it would never be possible to write a definitive article so I hope this will be a work continuously updated by the experiences of bat workers on the ground and geared towards our particular needs. Your feedback on this article will be invaluable in maintaining a useful resource for other bat workers. Please send any relevant information to me, Jules Agate at BCT ([email protected]), and please entitle the email Digital Recorders. Please note that I may not be able to answer each message individually straight away during the busy summer months. I am a bat biologist and not an expert in digital sound so please bear with me. Thanks! Bat Conservation Trust 2008 1 Digital Sound Formats: A Summary There are various formats of digital sound file that recorders may record into. Uncompressed sound files are usually in PCM WAV format. Files in WAV format are high quality being near representation of the original sound. Because they contain a lot of information, these files take up a lot of memory. The very cheapest portable digital recorders generally do not have a function that allows recording directly into WAV because the size the files need to be create problems for the player‟s file structure but happily the price of those that can have recently fallen and there has recently been a proliferation of models that can record into uncompressed digital files via a line-in. These tend not to be as small as the very cheap portable versions used mainly to play music. Other digital sound file formats include AIFF, mp3, mp4, WMA, AAC etc. The format refers to the type of audio data inside the file. File types are reflected in the file extension and refer to the structure of the data within the file so different file types can use the same format. The codec is the algorithm used to code information to get it into the particular digital format. A WAV format file has a WAV extension so the file name will be something like „longhollow 12-03-07.wav‟. This table adapted from Bruce Fries book (table 12) illustrates this: Format type Extension Codec MP3 .mp3 MPEG Audio Layer III Windows Media Audio (WMA) .wma Microsoft proprietary AIFF (Mac) .aif, .aiff PCM WAV .wav PCM PCM or Pulse Code Modulation is uncompressed but can be encoded in other formats to save space. It is a generic format and therefore can be read by most audio software so it is more compatible than most of the proprietary formats that require specific applications to be able to read them. This means that most sound analysis software can read WAV files coded in PCM and it is the default format for digital audio files on PCs but if your recorder is digitising into a different type of format some software may not be able to read it. BatSound for example can read PCM formatted WAV but not .wma or .aiff or .mp3. Some software like Adobe Audition can read or convert most file formats. Some recorders (Hewlett Packard for example) do code into WAV but not PCM WAV which BatSound and BatScan cannot read. The best thing to do is to open them up in something like audacity which is free or Adobe audition which can cope with other WAV types like AIFF WAV and re-save them as PCM WAV format. See our Sound Analysis Software factsheet for more information (available to download at http://www.bats.org.uk/helpline/helpline_learn_echolocation_bat_detectors.asp#Factsheet). Digital Sound and Compression In order to save space, digital sound files have been compressed over the past few years in various ways. Mp3 and minidisk formats both use a system of compression called Lossy audio data compression. This basically works by taking some information out of the file and converting it using an algorithm or code. Mainly devised for music, the information that is removed tends to be parts that are not important for human hearing and enjoyment of the music, so high frequencies and complex sounds are most affected. Bat Conservation Trust 2008 2 In theory this could affect the quality of the sonograms produced from recording bat calls from a detector to either minidisk or mp3. In practice, although there may be loss of some aspects of the signal and artefacts and additional noise may occur, it is still perfectly possible to analyse simple bat sonograms from recordings that have been compressed to a certain level. It wouldn‟t be appropriate for research looking at detailed call parameters, but for general analysis purposes it is adequate. There is an alternative in Lossless compression which works by encoding repetitive parts of a sequence with a series of symbols and equations which do not take as much space as the original but can be used to recreate it exactly. However, the highest compression rate is only 2:1 whereas Lossy can compress by 10:1 and hence it is usually favoured. Digital sound quality is measured by the sampling rate measured in kHz, the resolution in bits and the bit-rate measured in kilobytes per second. CDs with uncompressed sound quality sample at a rate of 44,100Hz (44.1kHz) 16 bit resolution and with a bit-rate of 1411.2kbps. Bit-rate refers to how many points the original sound is sampled at in order to digitise it and the higher rates result in better quality sound and a higher file size. The bit rate is determined by the sampling rate multiplied by the resolution and the number of channels e.g. CD quality is 44100Hz x 16bits x 2 channels = 1411200 bps or 1411.2kbps. Sampling rate is how many times a second the voltage of an analogue sound is measured to digitise it. Sampling rate affects the maximum frequencies that can be taken in (sampled). Only frequencies up to half the sample frequency will be digitised properly. Therefore your sampling rate should be twice as high as your maximum expected frequency (Nyquist‟s theory) in order for it to be digitised properly. So for bats at 110kHz (lesser horseshoes) which are reduced to 11kHz by either time expansion or frequency division factor of 10 at the detector, you‟d want to be able to sample up to 22kHz. In theory this means you could get away with a sample rate of 24kHz but in practice the high frequencies are still not sampled as well as the lower ones in the signal and may be filtered out. For this reason it is recommended that a digital recorder attached to a bat detector should have a sample rate of at least 32kHz and up to 44.1kHz to be sure of getting a good representation of the high frequencies. If a too lower sample rate is used it may distort or lose the higher frequency part of Myotis and horseshoe calls. A problem caused by a low sample rate is aliasing. If the sample rate is too low and the higher frequencies cannot be digitised properly, it can look as if the high frequencies in the call have been sort of folded down over the top of lower ones in the sonogram. These are not harmonics from the bat or another bat they are purely artefacts because frequencies higher than half the sampling rate could not be sampled correctly (see Jon Russ‟ book „The Bats of Britain and Ireland for a good explanation). Resolution is how precisely the binary representation in the digitisation process details the original audio sound. It is determined by the number of bits (1s and 0s) used in each sample in the digitisation process to represent the analogue sound. The more bits in each sample the more accurately each sample matches the original sound wave. High resolutions reduces distortion and background noise associated with the digitisation process, but it also makes the files bigger. CD audio quality is 16 bits per sample. Most recorders use 16 or 8 bits. When sound is compressed it is done using a code or algorithm to remove particular aspects from it therefore ending up with less data and a smaller file. Minidisks generally use a compression algorithm called ATRAC (adaptive transfer acoustic coding) developed by Sony. ATRAC is still used in Sony players but has been improved in the form of ATRAC3, ATRAC3plus and ATRAC Advanced Lossless. Other Minidisk manufacturers such as Sharp and Panasonic also implemented their own versions. ATRAC's original 292 kbps rate used on original Minidisks was designed to be 'close to CD quality', sonically but was still improved Bat Conservation Trust 2008 3 later. When minidisks first appeared on the scene, many bat workers were put off by the potential effects of compression but it soon became apparent that for identifying UK bats from field recordings they were usually of sufficient quality. Mp3 (or mp4) is a newer system for compressing sound and part of the MPEG family which are standards used for coding audio-visual information (e.g., movies, video, music) in a digital compressed format. Mp3 also effectively takes bits of the original information away and you can get varying sound quality depending on compression rates and algorithm encoders. The majority of mp3 players tend to use a bit rate quality of 128kbps to play back music as most humans find this satisfactory to listen to whilst still allowing a high degree of compression although compression can be done to a much higher degree with a lower quality result (down to 8kbps) or to a lesser degree with a higher quality result (up to 320kbps). Although in general, if the kbps is higher, usually less data are lost and the quality is better, this is slightly more complicated than it seems because different recorders and different programs use a variety of algorithms or codecs to encode the sound from analogue or WAV into mp3 and they may use different formula for compressing sound. This means that some produce better quality results than others, even at the same kbps setting. It is pretty difficult to find out what kind of codec is used in the various types of mp3 machines to encode the sound to mp3 format but current encoders include BladeEnc, Mp3 Producer, Lame, Xing and MPecker (Mac). Comparisons of the different codecs almost always refer to how it affects human perception of the sound rather than any measurement of specific parameters such as the degree of high frequency loss which would be interesting to us as bat workers. The larger manufacturers do provide on-line manuals that may mention what type of codec they use. Encoding into mp3 can also be done in different ways including constant bit rate encoding (CBR) and variable bit rate encoding (VBR). VBR is generally more efficient because it varies the bit rate depending on how complex the sound is so more complex sounds are sampled more frequently than parts with very little information in them and so it is more widely used. The main thing to be aware of is that mp3 file quality may vary between recorders because of the codec and not just the settings that you choose on your mp3 model. If you are interested in finding out more there is an easy to read MP3 and Internet Audio Handbook by Bruce Fries which includes an explanation of how sound is digitised, encoding and algorithms. For a comparison of the different audio algorithms see Wikepedia http://en.wikipedia.org/wiki/Comparison_of_audio_codecs. For all sorts of things relating to MPEG see http://www.mpeg.org/MPEG/index.html Potential Problems with Compression CDs are encoded at a rate of 1411.2 kbps. Original minidisks were encoded at 292kbps. Sony's official claim is that later minidisks using ATRAC3plus at only 64 kbps provide a quality comparable to MP3 at 128kbps (and similar claims are made by Microsoft for Windows Media Audio format). Although this could again be complicated by which mp3 codec they are comparing it to! Although Mp3 can be anything from 8bps (very compressed) to 320kbps the same as audio CD, 128kbps is used most frequently for playback as most people cannot distinguish it from CD quality yet the compression ratio is good. 320kbps is usually the top quality found in most mp3 recorders and is obviously much better for sound analysis purposes. Bat Conservation Trust 2008 4 Some aspects of sound like voice are easier to encode to mp3 or minidisk format than others so there may be varying quality of compressed audio data depending on the type of sound. Very fast changes in frequency and complex sounds are more difficult to encode. For an interesting direct comparison and explanation of the effects of compression by minidisk and mp3 see the article by Raimund Specht of Avisoft software at www.avisoftsaslab.com/compression.htm. Problems that occur in recordings due to compression are generally additional noise particularly with sounds that are rapidly modulated (like fast FM sweeps) or loss of information. According to Specht „if the available bit rate is not sufficient for encoding a given signal, the data reduction algorithm has to remove those parts of the sound, that are inaudible or less important for the human perception. This is done by reducing the bit-depths in some frequency bands. That procedure may produce additional spurious (quantization) noise in the decoded signal. Even more sophisticated algorithms as the bit reservoir feature of MP3 will lead to loss of information or distortion, as soon as complicated sounds last for more than a few milliseconds‟. In general this is not too serious for bat sounds which are simple and do not last for very long but rapidly modulated sounds could suffer from distortion noise. Perceptible distortion has been reported by some bat workers using some mp3 recorders at fairly low quality (128kbps or less). Ideally when recording to mp3 format, you want to record 16 bit resolution at a sample rate of 44.1 kHz and a bit rate as high as possible. I have an mp3 recorder that samples only at 44.1 kHz and has variable bit rates of 48, 64, 96 128, 160 and 192kbps. I have found that using 192kbps and 164 kbps has produced results that I can analyse satisfactorily. At 128kbps I have found some noise and artefacts creeping, in as well as loss of information, but it is difficult to actually quantify it and for example say what percentage of information is lost. When buying an mp3 recorder it is not always easy to find out what kbps level the recording via the line in is encoded at, whether the quality can be altered and what options you have for sample rates and resolution. Try to check manufacturer‟s manuals on line before you buy. Some recorders such as the newer models from Creative (Creative Zen V plus) have switched to wma (Windows Media Audio) compression for their direct encoding file formats. This is just an alternative format to mp3 but again is based on the Lossy compression and should deliver similar results. In the following pictures you can see the results from a recording of pipistrelles recorded in the same place using a Duet and an mp3 set at 192, 160, 128 and 96kbps (all 44.1kHz) converted from mp3 to WAV at the same time (these were not recorded simultaneously so it is not a direct comparison). All were 700ms of sound displayed using the same spectrogram settings on BatSound. Bat Conservation Trust 2008 5 Sonogram 1 Duet at 192 kbps 192 kbps Bat Conservation Trust 2008 6 Sonogram 2 Duet at 160 kbps 160 kbps Sonogram 3 Duet at 128 kbps 128 kbps Bat Conservation Trust 2008 7 Sonogram 4 Duet 96kbps 96 kbps It is virtually impossible to compare these unless the same recorder was recording the same pulses from the same bat and different compression rates but in general there does seem to be more noise associated with 128 and 96kbps. Choosing a Digital Recorder Capacity of Recorder and Cards The capacity that you need in a digital recorder will vary with the format that it uses and the quality you choose. A 1GB Compact Flash card or drive, for example, will hold approximately 100 minutes of uncompressed CD-quality 16-bit stereo 44.1 kHz WAV audio files. With most detectors it is not necessary to record in stereo and recording in mono will obviously be sensible to drastically increase the amount of recorded time you can get into the available memory. Formula for uncompressed .wav file size: Sample rate x resolution x no. of channels x time in secs bits/byte = File size in Bytes. So a 1 minute stereo file sampled at 44.1kHz and 16 bits where 1 byte = 8 bits will be: 441000kHz x 16 bits x 2 channels x 60 secs /8 bits/byte = 10,584,000 bytes Bat Conservation Trust 2008 8 Table of mp3 bit rates and file sizes. Time Mp3 bit-rate kbps File size MB 1min 96 0.703125 1 min 128 0.9375 1 min 164 1.201172 1 min 192 1.40625 1 min 320 2.34375 Taking the standard of 1024MB in 1GB, that same 1GB media will therefore store about 1500 minutes of stereo MP3 audio at 96kbps (1024/0.703125). There is a handy mp3 file size calculator at http://www2.le.ac.uk/projects/impala/documents/resources-and-tools-forcreating-podcasts/mp3-file-size-calcuator.xls/view Recorder Type The main types of digital recorder you can choose from are Mp3 (flash or hard drive) Solid State Hi-MD Digital Voice recorders PDA DAT Things to consider are cost of the unit, battery life, ease of use, robustness and cost and ease of using the removable media (CF cards, minidisks etc). Also think about what you are using it for – remote surveys vs. walking around with for example. Battery life is reduced in cold weather so that needs to be taken into consideration if you are going to be leaving it out to record swarming activity in the autumn. What kind of detector you have may well be a factor. With a good quality TE detector you could get away with using a lower quality recorder but using a frequency division detector you might need the best quality you can get to have the best chance of identification. An important point is whether you can easily replace it if you lose it and also just how safe you feel with it – if you are surveying a lot in certain urban areas a small, discrete job you can easily tuck away is probably a better bet than an expensive looking and smart model. If you are thinking of buying a new detector soon anyway, it may well be worth going for a cheaper recorder to go with your current detector now and looking in the near future at the detectors with flash cards within them (Anabat SD1, Pettersson D1000x and the upcoming Griffin from BatBox) - no more tripping over cables! A comparison of digital recorders in terms of microphone noise, some of which are listed in this document can be found at can be found on the Avisoft site under software tutorial. It is written by Raimund Specht at http://www.avisoft.com/recordertests.htm For a comparison of how different recorders perform in the field click on Avisoft‟s Making Recordings in the field link on the tutorial page. It compares the various models by handling, ruggedness, weight, sound quality, bandwidth and price which is really useful. It includes digital solid state recorders like the Edirol, Marantz and minidisks but not mp3 recorders. http://www.avisoft.com/tutorial_field_recording.htm. Bat Conservation Trust 2008 9 There is also a section on understanding microphone and recorder/preamplifier noise specifications at http://www.avisoft.com/tutorial_mic_recorder.htm. Sample rate and Quality The most important parameter in addition to the recording format (uncompressed or compressed) and capacity is the sample rate. The sample rate should ideally be 32kHz or 44.1kHz for recording UK bats from bat detetctors. There is no real need to go higher than this because it makes the files bigger but if you use a recorder with a lower sample rate you can get aliasing and loss/distortion of high frequencies (see section on Digital sound and compression above). The quality given at various bit rates has not been extensively tested with bat detectors but as a general rule of thumb 160kbps seems to not display much distortion and above that is probably fine for most purposes. Even lower quality would probably be OK for most basic i-d tasks as long as the sample frequency was sufficient but it may be an issue against noisy backgrounds and with reproducing bat signals that change frequency very quickly or use very high frequencies. MP3 Recorders There are basically two types of portable mp3 player/recorders - flash memory or hard drive. The major difference is their storage capacity. Hard drives usually have a much higher storage capacity than flash memory (100+ GB compared to 4GB). According to some reports hard drive players can suffer from skipping and dropping out especially if you are using them on the move. Flash mp3s are more stable as they have no moving parts. Hard drives may be more power hungry and drain batteries more quickly, but remember that technology is improving rapidly in this field. Flash mp3 players/recorders tend to be the cheaper option. Most very cheap models are players only, not recorders so check with any bargains you come across that it is a recorder and can record from external sources via a line in. Often shops don‟t list (and don‟t know) whether it does have a line in or not and then they don‟t know what format or quality the line-in encodes to. Ideally have a look to check and if they won‟t let you look and they don‟t know the specifications, don‟t buy it! With mp3 recorders, the budget models usually only record to mp3 format. This means you will then have convert the mp3 to WAV format for some sound analysis software to recognise (BatSound & BatScan) but not Wavesurfer which can handle mp3 directly. For more information see the BCT Sound Analysis Software fact sheet - available to download at http://www.bats.org.uk/helpline/helpline_learn_echolocation_bat_detectors.asp#Factsheet). Conversion is relatively easy using packages that you can download from the web usually for around 40 US dollars. I have been using All to Wave converter and found it simple and fast and DB Poweramp is another one worth checking out as the most simple package is free. For other options try a search for mp3 to .wav conversion software in any internet search engine. Some packages that come with mp3 hardware include a free converter. The problem with converting is that is another step during which corruption can occur and information can be lost or distorted. A few mp3 flash or hard drive recorders can still also record directly to WAV format so the sound is uncompressed but check they do have a line in. The advantage is better quality and no conversion is needed making the files easy to use and reducing the likelihood of error in the conversion process. You can (usually) copy files straight across from the player to your computer and open them up. The ones with this capability tend to be more expensive. Bat Conservation Trust 2008 10 Choosing an mp3 Model For online deals, information and good support for finding your way through the mp3 maze I have been recommending www.advancedmp3players.co.uk as it is fairly informative, lists models clearly by manufacturer, lists features, specifications and shows customer reviews. They are also really helpful through their technical support line and email. Another site www.mp3players.co.uk is not as informative although worth checking for offers. Mp3 features to look for: Capacity for direct encoding from external sources via line-in. Long enough battery life for your field work and preferably the ability to use normal or rechargeable AA or AAA batteries either instead of or as well as an internal rechargeable battery. Variable mp3 encoding quality (standard is 128kbps). Ideally you want to be able to go higher for better quality recording. Quality depends on encoding method but sampling at 44.1kHz at 192kbps is generally accepted as high quality (maximum is 320kbps). Frequency response range 20Hz to 20kHz (based on TE / FD x 10). Sampling rate should be 44.1kHz but 32kHz may do at a push if you are not trying to identify Myotis or if there are no horsehsoes Check case size/button size etc – you may prefer a small size for portability or slightly larger depending on your eyesight and finger size. 1GB memory capacity is ideal for most survey needs but you can get away with less. Models vary all the time, even more so than minidisks hence it is difficult to recommend a particular model. I have been using an MpEye TS400 since late 2005 and have had no problems using it with Duet and D240x. Unfortunately it is no longer available! It took a while to work out the buttons but is easy to record with little delay time in the field which is handy. It is also light, relatively simple to move around the menu and once set up recording is really easy just using pause on and off which are good features to look for. The major drawbacks are it has to be recharged via a USB / ac adaptor and does not have a removable battery and the recoding level cannot be changed and calls can be overloaded and clipped with loud bats flying close by, especially with the Duet which does not have a facility to alter the gain. Reliable manufacturers of mp3 include Creative, iRiver and Archos. Look around for deals via internet shopping sites like Froogle, Kelkoo and PriceRunner. Amazon and e-bay often have bargains worth checking out especially on older or end of line models. It may be cheaper to get newer ones from Europe or the USA. It is becoming very difficult to find mp3 recorder models that record at over 128kbps in mp3 format. Creative and I audio now both record into wma rather than mp3 via their line-ins. If you are thinking of buying a different make (and there is no reason not to if the specifications seem right), try and talk to someone knowledgeable in an electronics store, contact a technical support line and/or read the reviews. Be aware though that not many people are using them in the way we do for bat work and so things like ease of use in the dark, recorded sound quality via the line-in and delay times for commands is rarely reviewed by customers. Also some people are not technically minded and the reviews sometimes reflect their own shortcomings rather than the machine! If you can, go and have a look at the model in a store so that you can see how big the buttons and display are. You could also contact the manufacturer although we have found that the Creative customer support were not very helpful. Check the returns policy of the supplier in case it is not want you want. Bat Conservation Trust 2008 11 Check feedback about recorders and manufacturers posted on the BCT forum at: http://www.bats.org.uk/forums/bat_forums_index.asp Current Flash MP3 Recorders Creative Zen V Plus £45-63.00 Amazon.co.uk. A reputable company for good quality products. Has a line in and will encode from any source in wma format at 128kbps. Unfortunately creative customer help and support is poor. They always refer you back to the FAQs and product info on the website whatever question you ask and that gives relatively few specification details relevant to line-in recording. http://ie.europe.creative.com/products iRiver iFP If you can get hold of earlier i-River iFP models in the 700 and 800 series these are known to be very suitable for use with detector, recommended by Sonobat and BCI in the US (see info at www.sonobat.com). Later models have much higher compression rates (typically 64kbps per channel for the T30). The earlier iFP recorders are still sometimes available on auction sites such as ebay at knock down prices as low as £20 or less and so that is a good option if you are on a budget and you have the patience to wait for one to come up. Archos 605 4GB flash mp3 recorder is £119.99 at www.advancedmp3players.co.uk July 08. It has a line in and encodes direct to WAV format as well as mp3 but it has no external battery pack and so prior recharging is necessary. See notes about the Archos gmini models below. Hard Drive MP3 Recorders Hard drive mp3 players don‟t always have a line-in, especially the newer models that seem to be video orientated. Some do have a line-in and also record directly to either mp3 or mp3 and WAV. i-River x20 4GB available for around £75.00 as B grade model (some superficial damage) from www.advancedmp3players.co.uk or www.instockdirect.co.uk The x20 records in MP3 via a line in with highest quality of 128kbps and a sample rate of 44.1kHz which you could probably get away with. You can also record at the lower bitrates of 80 and 96kbps with a sample rate of 22.05 kHz but this would not generally be recommended for bats due to the potential for artefacts and aliasing. iAudio X5 and I Audio D2 D2 16 GB £159.99, 8Gb £128.99 and 4GB £99.99 The popular i Audio X5 had direct encoding via a line-in with a variable mp3 bit rate encoding of 32 - 320kbps. It works like an external hard drive when connected to your computer. No longer available new and has now been replaced by the iAudio D2. The D2 Line-in recordings are in compressed WMA format (Windows Media Audio) rather than mp3 and options are available up to 256kbs. It is not clear at what sampling frequency (but I have asked for this information and will let you know). It is probably between 8-32kHz and is via the optional line-in converter cable. Record gain level are manually adjustable but because it uses the WMA you generally have to convert from WMA to wav to edit. www.advancedmp3players.com and product info from http://www.cowonglobal.com/ Bat Conservation Trust 2008 12 Archos Gmini 400 20GB and Archos Gmini 500 40GB The Gmini 400 records directly to WAV and has been used for some time by Herman Limpens in the Netherlands. He reports that it is absolutely fine on the recording side and quality even of high frequencies is good. He advises that recording via the tape out from the D240x into it gives too weak recordings and so it is connected via the headphone out to the line in of the recorder. With the volume knob he then regulates the level/loudness of the recording, but the disadvantage is that he cannot then record via the comment switch as well. Headphones are then plugged into the recorder rather than the detector so that you can hear what is going into the recorder. Transferring the recordings to the laptop is easy via the USB and every recording has a number and date and time. In the field you have to start a new recording each time rather than pause and continue but it makes for good file organisation. The screen is very bright especially in a dark forest but can be set to automatic shut off in 3 secs and you can light your way in the dark with it. It does have very small knobs indeed and is not designed for handling in the field. Another disadvantage is that it automatically shuts off after a certain time, when not recording something. Herman comments that 'sometimes you suddenly start asking yourself why everything is so quiet and you might have missed something'. It also consumes the battery very fast. Mostly it is necessary to charge it again in the midnight break if you are working all night as Herman frequently does! At BCT we have found the adaptor for the line in is weak and it is very specific to the Gmini so if you need to replace it will cost about £20. Also the battery starts to become weaker after about 1 year. The 500 is similar to the 400 with a larger memory and is still available at around £240 from http://www.purelygadgets.co.uk/ and a special offer of just £120 from www.superfi.co.uk (July 2008). Both models can play video and store/display photos as well as sound. Solid State Digital Recorders These are commonly used by musicians, journalists and wildlife recording enthusiasts as generally they give a very high quality sound and can record directly to WAV, although you can usually alter the file format and bit rate to set the quality as you choose. The difference is that they usually record onto memory cards which means you are not limited by the internal memory size and they can record directly to uncompressed WAV format. However, they tend to be pricier. They are also robust as they have no moving parts and some are designed for use in the field with features like lock-down panels to prevent switches from accidentally being changed. You can buy compatible external microphones and relay switches for some models which make them ideal for remote recording and other wildlife as well as bats. Usually the memory cards that come with them are not that big but replacement 1GB cards are becoming cheaper all the time. Be careful with cards larger than this as some older models and flash card readers can‟t read them. Makes that have been recommended and used include the Swissonic, the Edirol and the Marantz. The others are a bit more of an unknown quantity. Bat Conservation Trust 2008 13 Solid state Digital Recorder Models (in vague order of lowest price to highest) New! Swissonic MDR-2 Swissonic are owned by Thomann who sell this budget model for 95 Euro or £74.50. The NBMP Bats & Roadside Mammals survey recommended this model which is extremely good value for money. It records at 44.1 kHz in either WAV or MP3 stereo. It has an internal built-in 128 MB flash memory (up to 2h of MP3 recording) and also takes separate SD Cards (16MB-2GB), or SDHC (4GB) cards. Recording formats: WAV: 8bits/11kHz, 16bits/22kHz and 32bits/44.1kHz. The MP3 is 128kbps at 44.1kHz so preferably use the WAV format. Frequency range is 20Hz to 20kHz. Requires two (Mignon) AA-batteries (up to 5h recording) or rechargeable batteries. USB 2.0 full speed compatible and includes an external stereo mic and USB-cable. Measurements 155x 85x 30 mm. Weight: 200g. Feedback from car survey users so far is that it is pretty bulky and plasticky and the buttons are big. Also it requires 2 3.5mm to 6.5mm adaptors and stereo mono splitting lead to record in stereo. You can get these from Maplin but it is a bit of a pain, although for the price you may think it is well worth a bit of inconvenience. One user on the BCT forum reported that although it made good recordings, it had a frequent tendency to freeze-up and sometimes would not turn off. http://www.thomann.de/gb/swissonic_mdr2.htm New! Roland Micro BR Costs around £139 from instruments togo.co.uk but other places the price is as high as £170 so shop around. However, it is still a much cheaper option than the Edirol and Roland are very good quality generally. It is also a 4 track mini studio as well as a digital recorder in case you fancy laying down drum beats and vocals while waiting around for bats! It has three mp3 recording compression options: Best quality 192kbps at 44.1kHz Standard 128 kbps at 44.1 kHz Long play 64kbps at 44.1 kHz Best quality would be OK but it also records in to WAV format 16 bit 44.1kHz. It uses SD cards and again comes with a paltry 128MB so you need to replace that. It measures 136.0mm x 81.0 mm x 21.4 mm. The official blurb says “even though it‟s a shrimp, the Micro BR packs an entire studio worth of features into its tiny case. There are a dozen buttons on its front panel, nine knobs, and even a built-in microphone for quick capture”. This might be encouraging for musicians that love different effects but is slightly worrying for bat workers as too many knobs could be a hindrance. Still, the price is very competitive and sound on sound have done a good article and review which will help if you want to use as more than just a basic recorder. Specifications http://www.roland.co.uk/guitar_room_catdet.asp?ID=MICROBR Review http://www.soundonsound.com/sos/feb07/articles/bossmicrobr.htm?print=yes New! Samson Zoom H2 Costs around £150 - £175 The H2 is an attractive looking little device for stereo or 4 track which records on Secure Digital (SD) media with a 512MB SD card included in the price. It can take a 4GB SD memory card and comes with an 1/8 inch stereo to RCA cable, mic clip adapter, tripod stand, USB cable, and AC adapter. The H2 is small and light at .110g and measuring 63.5mm(W) x 110mm(D) x 32mm(H). Two standard alkaline AA batteries power it and give 4 hours continuous recording time. Recording options are WAV at 44.1/48 or 96 sampling frequency and 16 or 24 bit and mp3 samples at 44.1kHz with a very wide choice of compression options at 48/56/64/80/96/112/126/160/192/224/256/320 kbps or you can select VBR mode. Bat Conservation Trust 2008 14 It has a built-in 3-capsule condensor mic (giving surround-sound recording if used with a mic) and also has a time-stamp function (unlike the H4). It also uses a standard 3.5mm stereo jack into the line-in. The website even has a little tutorial and you can also download the user manual (specifications page 86-87). Seems like a good all round option and good value. http://www.samsontech.com/products/productpage.cfm?prodID=1916 M Audio Micro Track 24/96 4-5 hours battery life and average about £200. Simple-looking, hand held unit that records both WAV and MP3 files to Compact Flash via line input. Also has built-in high-fidelity microphone preamps for studio-quality microphone input but make sure you get the correct leads and adaptor as they are 1/8 rather than ¼ (adaptor available from Maplins). Connects to the computer via USB. Powered from a lithium-ion battery, and recharged via the computer‟s USB connection or USB power adapter. A potential problem flagged up last year with battery replacement has cropped up in the BCT owned machine. Over time we have found it takes longer to charge and also the battery is running down very much more quickly one year after purchase – it now cannot manage a whole field night. It is also really liable to get switched on accidentally if you do not put the hold on resulting in arriving at your survey with a tiny bit of charge left and no way to supplement it with AA batteries. To replace the battery it needs to go back to manufacturer so that is a real downside. In the field it was easy to use with big buttons and a nice clear display that you can leave on or choose to go off. It does not take external batteries so you must remember to charge it up. The jog wheel is a bit too easy to move so you can accidentally change settings unless you put the hold on but it can record in WAV at 44.1, 48, 88.2 and 96 kHz and 32, 16 or 8 bits. Mp3 options are 96, 128, 160, 192 and 224kbps. It is quite big compared to an mp3 flash (10cm x 5.5cm) but is not heavy. You do need to select the correct input source or you won‟t record anything. It takes a bit of trial and error to establish the best settings in terms of gain on the detector vs recording level on the recorder. Loud calls can easily get overloaded and clipped if your gain and recording levels are too high (with Pettersson detectors you can alter the gain). A handy feature is that it tells you how much recording time you have left on the card and it is really easy to delete unwanted tracks if you start running out of space. It comes with an external electret microphone so you can use it as a Dictaphone as well. It comes with a very measly 128MB card that will give you only 12 minutes of standard 44.1 16 bit WAV recording so you need an extra card with bigger capacity. It is very easy to copy files over to computer and just shows up as a mass storage device through the USB to copy the files straight to the hard drive. http://www.m-audio.com/products/en_us/MicroTrack2496-main.html Samson Zoom H4 Available from Amazon for about £220. Also records up to 24-bit/96 kHz digital audio WAV as well as MP3 up to 320kbps. The Zoom H4 features two studio-quality electret condenser microphones and like the Microtrack uses two1/4-inch input jacks. The Zoom H4 records on to Secure Digital (SD) media, and a 128MB SD card is included with the unit so again you will need to buy cards. Also works as a mini recording studio as it has a 4-track recording mode and guitar and bass amplifier modelling effects. The advantage over the Microtrack is that it does run on 2 AA batteries from which it claims to give 4 hours of continuous recording. Again it does not need any special software to copy files across. http://www.samsontech.com/products/productpage.cfm?prodID=1901 Review http://www.soundonsound.com/sos/dec06/articles/zoomh4.htm?print=yes Bat Conservation Trust 2008 15 Edirol R-09 and R-09HR R-09 is £259 from Alana ecology but it does crop up on other sites and ebay and for less. R-09HR currently around the same price from www.solidstatesound.co.uk for example. The Edirol R-09 has been very well received recorder among many bat workers in recent years for ease of use and high quality results. It uses SD memory cards. The popular Edirol R-01 model can still be found in some places (try E-bay) but was replaced with the Edirol R-09 which is as good and a bit easier to handle in the field. It is a very handy size but still has a nice big record button, a useful ability to alter the recording volume and also the headphone volume easily and it is also easy to use the menu to change recording settings. The display is very bright but you can change the time it stays on. Only a minor irritation is that to make a new track you need to press stop and then record again, which is a bit annoying if you are trying to deliberately put different species on different tracks. Both use AA batteries. It has now also been superseded by the R-09HR. This looks very similar both record in WAV format 44.1/48kHz sampling frequency but the R09HR also can sample up to 88.2 and 96kHz. Mp3 recording quality options are the same in both at 64/96/128/160/192/224/320 kbps at 44.1kHz or 48kHz. The battery life in the newer R-09HR model is 30 minutes longer and it comes with a remote control and audio creator software. It also slightly heavier at 174g compared to 145g for the earlier model and dimensions are 62mmx113mmx27mm which is similar to the R-09. A comparison table of the features of the Edirol R-09 and the 09HR can be found at http://www.solidstatesound.co.uk/R-09HR_Comparison.pdf. Reports from many bat workers suggest the newer Edirol model records at a quieter recording level and if connected from the Pettersson D240x tape socket to the Edirol 09HR line in you will struggle to get a decent signal. Experimenting with it so far by various bat workers seems to show that the best bet is to opt for connecting your Pettersson via the HEADPHONE output to the line–in of the Edirol instead. The headphone output is much louder but then of course it is affected by the detector volume dial. You can still listen to the headphones plugged into the recorder though so you can hear what is being recorded. Using the Mic socket instead of the line-in on the Edirol did not seem to improve things that much. Edirol website http://www.edirol.net/ NEW! Olympus LS 10 Costs around £257- £300 new online (£257 at time of writing from www.dv247.com). Olympus‟ answer to a portable solid state digital recorder can go up to a 24bit/96kHz sampling rate in WAV recording and also WMA and MP3 recording formats are available. Has a 2GB internal memory but can also use SD / SDHC cards (512MB - 8GB). This model has built-in stereo 16 mm round dynamic speakers and uses a standard 3.5 mm mini-jack for the line-in. Power Supply Two AA batteries (LR6 or ZR6) or two Ni-MH rechargeable batteries and Alkaline battery life is 12 hours in record mode 44.1kHz 16 bit WAV. Rechargeable Ni-MH battery life is 16 hours in 44.1kHz 16 bit record mode. Weight 165 g (incl. battery) and dimensions (WxHxD) are 48 x 131.5 x 22.4 mm. It runs with Microsoft Windows 2000/XP/Vista, Macintosh OSX 10.2.8 - 10.5. http://www.olympus.co.uk/consumer/2581_digital_recorder_ls-10_18555.htm Bat Conservation Trust 2008 16 Marantz New! PDM 620 = £235 and 4 hours battery life PDM 660 = average about £350 and 4 hours battery life PDM 670 = 7 hours battery life for £500 PDM 671 = 40 assignable quality settings from 32-384 bit rate for £600 and quite a bit bigger and more complex than the hand held 620 or 660 but good for research uses. Marantz have also come up with their own mini hand held digital recorder the PDM 620. It is a similar price to the Edirol; it looks quite rugged with fairly easily located and rubberised buttons and is a tiny bit smaller than the Edirol at 62 x 102 x 25 mm. It uses 2 x AA alkaline or Ni-MH batteries typically giving up to 4 hours operation and has a battery life remaining indicator. The line in is via a standard 3.5mm jack. For recording you can choose between 16 bit or 24 bits, 44.1 kHz or 48 kHz sample rate, and six MP3 bit rates from 192 kbps to 32 kbps. It uses SD cards and SD High Capacity cards are supported with recording file size limited only by the card size available. Use of cards for up to 2 terabytes will be possible (" TB) when these become available. View the Marantz 620 with a demonstration video at www.ndeva.co.uk/index.php?281&backPID=281&tt_products=824 The Marantz 660 is a fairly advanced recorder and external microphones can be bought to make it ideal for wildlife recording other than bats. It is slightly more complex to use than the Edirol, has more functions, and more settings and is not so easy to use in the hand especially when combined with bat detectors etc but reportedly makes excellent quality recordings. http://www.marantz.com/new/index.cfm?fuseaction=Front.MarketHome&cont=eu&bus=hf Korg Mr1 Professional 20GB Around £429.99 from www.dv247.com & £450 Amazon. The hand-held MR-1 apparently uses high quality 1-bit / 2.8 MHz recording and supports multiple recording formats including DSDIFF, DSF and WSD 1-bit formats (see the Korg page for info on these). It can also use the standard multi-bit PCM format that all of the other types use with resolutions up to 24-bit / 192 kHz. 1-bit recording is the latest advancement in audio with “uncompromising fidelity, low noise floor, extended dynamic range, lifelike imaging and analogue quality depth”. The 1-bit format can also be converted into WAV and AIFF formats at various bit-rates, bit depth and sample rate without error or degradation through Korg‟s included AudioGate™ software (Mac® and PC). It has an internal 20GB hard drive and can transfers data to computer via USB 2.0 connection. A large backlit LCD offers optimum visibility under all lighting conditions. Comes in a functional soft case that allows the recorder to be used without having to remove it from the case (which sounds quite handy). Powered by rechargeable lithium polymer battery, it seems pretty pricey although it no doubt has exceptional audio quality but probably a little over the top for most of our purposes. It is highly unlikely I would ever shell out the BCT budget on one of these! More info about this model and 1 bit technology can be found at http://www.korg.com/mr/ Bat Conservation Trust 2008 17 Hi-MD Standard minidisks are becoming obsolete and most models require you to spend time recording the tracks you have filled up with bat sounds from the minidisk back to the computer manually through the sound analysis package (although BatSound does have an auto-record feature that allows you to leave it to record automatically). The digitisation takes time and also presents the opportunity for things to go wrong and data to be lost so minidisks are not the ideal choice when digital options are available (but are useful as a back-up). Sony‟s Hi-MD recorders allow you to record in digital format and copy the files across a USB port without needing to re-record the disk contents into a software program. They also have up to 305MB capacity per disk. The first models of the Sony Hi-MD were fiddly and especially difficult for setting the correct recording levels which required you to key in a code and then reset every time you used it. The software also presented problems when trying to copy files across in a specific order. The later models (Hi-MD RZ-RH1) recorded in uncompressed PCM format at 16bits/44.1kHz which is similar to CD format and offers ATRAC3plus encoding at 256kbps (Hi-Standard Play) or 64kbps (Hi-Long Play). The only problem is that these Sony Hi-MDs require the installation and use of a program called Sonic Stage to enable the files you create by recording the bats to be copied across to your computer. The software is free with the recorder but it is not a particularly easy program to use and is yet another stage to have to get to grips with. The Hi-MD RZ-RH1 also apparently uses a Sony Li-ion rechargeable battery and doesn‟t have the additional AA battery capability of earlier versions which means you need to be organised and remember to charge it up or get hold of an external USB battery pack. The Hi-MDs are generally not available new any more but they come up very often on e-bay and sell for around £50 sometimes with a lot of extras thrown in. For more info see www.minidisc.org/hi-md_faq.html which is where a lot of this section is taken from but also provides more technical details and comparisons of Hi-MD and standard style minidisk technology if you are interested. Digital Voice Recorders The cheapest option by far is to go for a digital voice recorder. The recorders usually record into WAV format and have a limited memory but they can be set in voice activated mode which means they will record automatically only when a sound triggers recording to start. This makes them especially suitable for using in a remote survey set-up connected to a bat detector like a Pettersson D240x or a D980 on auto trigger mode so it fires only above a certain threshold (either volume or frequency). Bob Cornes of Beds BG has been using an Olympus VN-240PC Digital Voice Recorder in this way for some time. There are several models in the same range, differing in memory size. He says that memory is unlikely to be an issue for most uses, although it is necessary to use the high quality recording mode which is heavier on memory than the other modes. It uses 2 AAA batteries and Bob says: “Using NiMH rechargeable gives 2-3 full nights before recharging, depending on conditions and amount of bat activity. If you wanted more battery power, you could always use an external battery pack - this is what I've done with the Pettersson D240X. One factor that caused me trouble initially with the remote set-up was low temperatures on spring nights, which drained the batteries remarkably quickly. I got round it by lining the box containing the Bat Conservation Trust 2008 18 detector and recorder with foam insulation”. The advantage is you will not have lots and lots of dead time to listen to so it is an efficient method of recording though if you left it outside a busy roost it could fill up. The downside with digital recorders is that the sampling rate is generally not sufficient to capture the highest frequencies and the quality is very low. Ideally for UK bats the sampling frequency should be 44.1kHz (32kHz at the least where horseshoes are not present) but many of the digital voice recorders only record up to 16kHz at best quality which means you will cut off the highest frequencies in some bat calls and may get aliasing. Be careful if selecting lower quality – Sample rates for the Olympus VN-240 are 16kHz at best quality, short play is only 10.6kHz and LP mode is 5.75 kHz – the SP and LP modes are therefore pretty much useless for recording bat sounds and it would not be advisable to use any digital voice recorder at all if you are trying to identify the Myotis or where horseshoes are present. The Olympus VN-240PC 32MB memory records 1h 28 in high quality mode. It costs about £60 from Amazon and only £40 from Pixmania.com. There are models with more memory available – look at „notetakers‟ on the Olympus website. The VN 480 is 64MB and around £100 or less but read the specifications to check the sampling frequency. http://www.olympus.co.uk/voice/ Please note prices given are a quick guide based on checks made at the time of writing (July 2008). You may be able to pay less or need to pay more depending on stock availability etc. Acknowledgements: Thanks to the following people for valuable information: Bob Cornes, John Haddow, Brian Harrison, David Lee, Herman Limpens, James Paterson, Martyn Cooke, Jon Russ, [email protected] Further Info on the Web Digital Sound and recording General Wikepedia http://en.wikipedia.org/ Comparison of codecs http://en.wikipedia.org/wiki/Comparison_of_audio_codecs How stuff works http://videos.howstuffworks.com/mp3-player-video.htm Digitising sound and mp3 http://www.teamcombooks.com/mp3handbook Comparison of mp3 and minidisk www.avisoft-saslab.com/compression.htm SD/flash memory card info http://en.wikipedia.org/wiki/Secure_Digital_card Wildlife recording http://www.wildlife-sound.org/ BCT forum link http://www.bats.org.uk/forums/bat_forums_index.asp Price Search Pricerunner http://www.pricerunner.co.uk/ Kelkoo http://www.kelkoo.co.uk/ Froogle http://froogle.google.com/ Bat Conservation Trust 2008 19 New Models and Reviews Information http://www.soundprofessionals.com/ Online expert reviews at Sound on Sound http://www.soundonsound.com/ reviews the Edirol, Zoom H4 and the Roland Micro BR Or see less consumer reviews http://www0.epinions.com/MP3_and_Digital_Media_Players Alana Ecology advice on recorders http://www.alanaecology.com/ and follow the link on recorders page to choosing a digital recorder. Mp3 All about mp3: http://www.allaboutmp3.co.uk/Mp3_players_Features.html Mpeg resources http://www.mpeg.org/MPEG/index.html Mp3 file size calculator http://www2.le.ac.uk/projects/impala/documents/resources-and-tools-forcreating-podcasts/mp3-file-size-calcuator.xls/view Supplier www.advancedmp3players.co.uk Supplier www.mp3players.co.uk Solid State Recorders Supplier/info http://www.solidstatesound.co.uk/ Supplier / infohttp://www.sound-light-company.co.uk/ Supplier http://www.dv247.com/icat/Digital+Recorders+%26+Players/2949/ Edirol http://www.edirol.net/ Marantz http://www.marantz.com/new/index.cfm?fuseaction=Front.MarketHome&cont=eu&bus=hf M Audio http://www.m-audio.com/products/en_us/MicroTrack2496-main.html Samson http://www.samsontech.com/products/productpage.cfm?prodID=1901 Korg http://www.korg.com/mr/ Hi-MD www.minidisc.org/hi-md_faq.html Digital Voice Recorders http://www.olympus.co.uk/voice/ Bat Conservation Trust 2008 20 ">

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Key features
- Digital Sound Formats
- Choosing a Digital Recorder
- Sample rate and quality
- MP3 Recorders
- Digital Voice Recorders
- Solid State Digital Recorders
- Hi MD
- Choosing an mp3 Model
- Current flash mp3 recorders