Understanding Audio Levels
A basic understanding of the general audio levels mentioned in this lesson will help you avoid
the common mistakes often made when connecting audio devices together. We are going to
talk about three different general levels of audio signals. The names of the three general
audio levels are speaker level, line level and microphone level. For simplicity, the different
audio levels are described in volts. For an understanding of decibel levels used in audio, see
Appendix 2 on decibels. .
Speaker Level
A speaker needs a few volts of electrical audio signal to make enough movement in the
speaker to create a sound wave that we can hear. Small speakers need only a few volts, but
large speakers need 50-100 volts to make a loud sound.
Line Level
A speaker is connected to an amplifier. Think of your HiFi amplifier at home. What plugs into
your amplifier? DVD player, CD player, radio/tuner, video camera. All these devices plug into
the “line in” or “Aux in” of your amplifier. "Line IN", "Aux IN" and "Line OUT" all have an
electrical audio signal at line level.
You are probably aware of the standard red and white leads used in HiFi
equipment, these all use line level. Other plugs are also used for line
level. Line level is about half a volt to one (½ - 1) volt. It is the job of the
amplifier to amplify the half to one volt of line level, up to the 10 volts or
more of speaker level.
Note: A common error is to connect plugs and sockets together just because they fit. Don't
assume audio level based just on the type of plug being used. The same type of plug can be
used for different purposes (and different audio levels).
© 2015 Geoff the Grey Geek
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Understanding Audio Levels
Microphone Level
Ok , so we have line level (about ½ - 1 volt) which goes into an amplifier to make it up to
speaker level (about 10 volts or above). What audio level do you think Mic level is? How
much voltage do you think comes out of a microphone, as a result of you speaking into it?
Answer: Stuff all!
The output voltage of a microphone is very low. It is measured in milli-volts, that is 1/1000th
of a volt. A mic can give as little as 1 mV, or up to 100mV, depending on how loud you speak
into it. That is not very much. So what do you think is going to happen if you plug a mic
directly into the line in of an amplifier? Answer: A very low level of muffled sound if anything.
Mic Pre-amps
The amplifier wants line level, ½ – 1 volt to produce enough signal to make the speaker work
properly. But the mic is only producing milli-volts. So what is needed is a small microphone
amplifier that amplifies the audio level from mic level to line level. This should go between
the microphone and the amplifier. Because it is for the microphone and it is before the main
amp, it is called a mic pre-amp. A mic pre-amp amplifies the milli-volts from a microphone up
to line level.
Mic pre-amps are normally built into devices designed for connecting to a microphone.
Equipment like an audio mixer, a digital recorder, a video camera or a computer - all these
may have mic level inputs as well as line level input, or just a mic
level input. .
The picture on the right shows for each input on this mixer there
is a line level input (labelled Line 3 and Line 4), as well as a
microphone pre-amp (labelled MIC PRE).
Obviously a microphone plugs into the mic input, as the mic
inputs are connected to the in-built mic pre-amps.
A line level device would obviously plug into the line in socket.
But what if your mixer (or computer/recorder) only has a microphone input, and you need to
connect a line level source to it? This would result in the line level (½ - 1 volt) being connected
to the input of the mic pre-amp. The trouble is, the mic preamp is expecting only a few millivolts. The resulting sound will be very distorted as the mic pre-amp is completely overloaded.
© 2015 Geoff the Grey Geek
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Understanding Audio Levels
So how can we do this? How do we connect a line level to a mic level input? We have to
reduce the line level down to mic level. The technical word for this is to attenuate the signal.
As an amplifier amplifies, or boosts the signal; an attenuator attenuates, or reduces the
You can buy attenuators at a music shop, they are called DI boxes. DI stands for Direct Input,
Direct Injection, meaning you can directly inject a line level into the mic input without any
Audio Level Summary
There are three main audio signal levels: mic level (millivolts), line level (around 1 volt) and
speaker level (around 10 volts or more). The rule is, only plug speakers into the speaker
socket of an amplifier; only line level into the line in of any equipment; and only mic level in
the mic input of your mixer, camera or laptop. The most common cause of audio distortion
comes from not understanding the different levels, and how to connect them all together.
Practical Example 1
Scenario: A keyboard (electric piano) located on the stage needs to connect to a mixer
located at the back of the hall, with a microphone multi-core cable connecting between the
Issue: The output of the keyboard is at line level, and the microphone input at the mixer
requires mic level. (There is also the issue of different plugs and balanced/unbalanced inputs
but these are the topics of other lessons).
Solution: Use a basic DI box available from most music or electronic stores. A DI box acts as
an attenuator which reduces the line level of the keyboard to mic level for direct connection
to the mixer (via the multi-core cable). The DI box also overcomes the issues of matching
plugs and going from unbalanced to balanced - so this is a perfect solution. This solution also
works for connecting electric guitars, electronic drums and DVD players.
Practical Example 2
Scenario: The output (line level) of an audio mixer needs to connect to a digital camera or
digital recorder which only has a microphone input.
Issue: The output of the mixer is at line level, and the microphone input of the
camera/recorder requires mic level.
© 2015 Geoff the Grey Geek
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Understanding Audio Levels
Solution: A basic DI box could be used, but this would require an input lead, and output lead
and the DI box - a lot to carry in your camera bag. A neater solution is to have a lead with a
40dB attenuator built into it. This will reduce the line level from the mixer by a factor of 100,
which will bring the line level down to a reasonable mic level to connect directly to the
microphone socket of the camera/recorder.
© 2015 Geoff the Grey Geek
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