Off-Ramp 5 User Manual rev 2.0
Off-Ramp 5 User Manual
Empirical Audio Rev. 2.0
© 2012
Off-Ramp 4 User Manual
Empirical Audio Rev. 1.0
1. Function/Technology
The Off-Ramp 5 is a versatile hi-res compatible USB interface. The function of the OffRamp 5 is to convert USB signaling into S/PDIF, AES and I2S so that a DAC can be
driven with a computer audio data stream. The Off-Ramp 5 reduces jitter in the digital
data stream by re-clocking using local oscillators. The Off-Ramp 5 incorporates our best
low-jitter technology and includes an array of technical advantages over other devices on
the market, including:
Async USB, so the master clock is in the Off-Ramp, not the computer
Inputs are re-clocked and I2S, S/PDIF and AES outputs are re-clocked again for
lowest jitter
External DC power source, allowing battery power or other supplies
Separate input and output circuit power regulation
High-quality discrete voltage regulation with Hynes regulators
Precision impedance-matched high slew-rate S/PDIF and AES/EBU outputs
I2S output interfaces for lowest jitter
Modular design to allow for clock, power and USB improvements and upgrades
These technical advantages allow the Off-Ramp 5 to be a world-class digital source,
leaving even the most expensive CD transports and USB converters in the dust.
The sound of the Off-Ramp 5 is unlike any other digital source. The clarity and imaging is
unsurpassed, allowing you to “see” into the soundstage more than ever before. Width
and depth are improved significantly. It is a totally immersive experience, the way that
music playback should be. More like vinyl, only better.
1.1. What is jitter?
Jitter is the number one problem limiting the performance of digital audio. Jitter creates
an unnatural, harsh and sibilant sound that is pervasive in digital audio. Jitter causes
listening fatigue with both CD players and computer audio devices. It’s only in the last
three years that the audio industry has become sensitive to jitter and started actively
addressing this. The sound of jitter is like looking through a window with a film on it.
When jitter is reduced, it is like cleaning the window and finally seeing the scenery
outside with crystal clarity and vividness.
Jitter is the inaccuracy in the timing of the digital data. It is not data errors, it is
inaccuracies in the timing of the presentation of the data to the D/A converter. This is
different than sending digital data to a printer for instance, or even a hard-disk. These
data transfers are not “real-time”. Streaming audio data from a CD transport or a
computer source is real-time because the D/A converter creates a real-time analog signal
from the data each time a new data word is presented. If the timing of the presentation of
each word is inaccurate, this causes frequency modulation distortion. There is nothing
that can be done about the samples in the recording and the clock that was used to make
those samples, but playback jitter can be minimized. This is the role of the Off-Ramp 5.
The Off-Ramp 5 virtually eliminates the sibilance and harshness due to jitter, making your
digital playback closer to analog. The Off-Ramp 5 is a truly unique and remarkable
product. Once jitter is minimized, the clarity, image focus and dynamics are improved
significantly. Even bass-tightness improves. Recordings of rain, thunderstorms, violins,
cellos, bongos and timpani are finally lifelike.
1.2. Theory of Operation
The primary function of the Off-Ramp 5 is to convert USB streaming audio format into S/
PDIF, AES/EBU or I2S formats and provide hardware interfaces in order to be compatible
with DACs. The Off-Ramp 5 is a re-clocker, meaning that the timing of the data flow into
the device is retimed using internal clocks. This has nothing to do with the timing or
tempo of the music. Because it utilizes an asynchronous USB interface, the master or
system clock for your audio system is located in the Off-Ramp 5. This clock provides the
timing for the dataflow from the computer source. This is the optimum way to achieve
low jitter.
The Off-Ramp 5 reclocker inserts between your computer or USB source and your DAC.
The data stream is not modified or upsampled in any way, it only passes through. The
only cable that is critical to performance is the cable between the Off-Ramp 5 and your
DAC. This should be a high-quality S/PDIF coax, AES/EBU or I2S cable to minimize jitter.
The USB cable can also be improved for even better sound quality, however the Belkin
Gold supplied is quite good.
1.3. Performance of different outputs
The four outputs all deliver world-class performance, however in highly resolving systems
some differences may be audible.
The I2S outputs deliver the lowest jitter, for those that have DACs with these types of
inputs. Next best in performance is the S/PDIF or “coax” output. Finally the AES/EBU
output is last because it requires an additional buffer to achieve the higher AES voltage
spec. In most systems the differences are minor however and may not be audible.
For non-Empirical Audio DACs with no I2S input, we recommend using the S/PDIF output
with a high-quality 1.5m length S/PDIF coax cable.
1.4. Internal clocks and clock quality
The Off-Ramp 5 comes standard with two clocks or free-running oscillators. Two clocks
are required because the asynchronous USB interface uses free-running clocks rather
than clocks that are synthesized from a single oscillator frequency. One clock is required
for the sample-rate group 44.1/88.2/176.4kHz and a second for the 48/96/192kHz group
because the two sample-rate groups are not related.
These clocks can be upgraded, improving the jitter. The Turboclock is our latest dualclock upgrade, taking the Off-Ramp 5 to a new level that is unchallenged by other
products in the marketplace. The Turboclock improves primarily bass tightness and
impact, giving the bass more focus and body. These clock upgrades are not userinstallable.
2. Front-Panel:
Power LED
Green indicator indicates DC power is applied to the DC input on back-panel.
Data Error
Yellow indicator indicates that data stream is corrupted or not PCM.
USB Mute
Red indicator indicates that USB signal is not being outputted. Generally occurs
when a track is stopped or paused. Mutes the HDMI I2S output for PW DAC.
Sample-Rate LEDs
One LED Illuminates to indicate the sample-rate of the incoming datastream.
Only illuminates when the USB Mute LED is off.
3. Back-Panel
3.1. 12VDC Input
This is the power input for the Off-Ramp 5. The power from this input goes directly to
the voltage regulators, and any installed clock upgrades, so the quality of this power is
critical. Upgrades here make an immediate difference in jitter. Average power
consumption is up to 500ma, depending on clock options, but much higher transient
currents are possible. The connector is center positive, 2.5mm and protected from
reverse voltage. To power-on the Off-Ramp 5, plug in the AC adapter and then connect
the DC power cable to the Off-Ramp 5.
3.2. USB Input
The USB input connects with a standard A-B USB cable to a computer or other
streaming USB audio source. The streaming rate limit is 24-bits, 192kHz. The USB
interface is asynchronous, so USB 2.0 compliant ports on the computer must be used.
The USB cable can be as long as 5 meters or 16 feet. To prevent application and
system crashes, it is best to close the music player application, such as iTunes, Amarra
or Foobar BEFORE disconnecting the USB cable. Make sure that you load the USB
driver into the computer before connecting the USB cable for the first time.
It is recommended that you close your player application (such as Amarra, Pure Music,
Foobar etc.), before you unplug the USB cable from the Off-Ramp 4 or computer. Then
restart the application after the USB cable is reconnected.
3.3. S/PDIF Coax Output
The S/PDIF coax output (optionally AES/EBU output) is the primary output that will
connect to most DACs. The output impedance is 75 ohms. The cable that connects
from this connector to your DAC should preferably be of highest quality and match the
75 ohm impedance. The S/PDIF output is transformer-coupled and isolated from earth
ground. The cable attached to this connector should be at least 1.0m in length, but
minimize the length beyond that. 1.5m is usually perfect and will work best with other
gear. The internal cable in the Off-Ramp 4 also has 75ohm characteristic impedance.
3.4. AES/EBU Output
The AES/EBU output is on a gold-plated XLR connector. Pin-out is standard pin1-Gnd,
pin2 plus or non-inverted signal, pin3 minus or inverted signal. The output impedance
between plus and minus conductors is 110 ohms. The output is transformer-coupled.
The cable attached to this connector should be at least 1.0m in length, but minimize the
length beyond that. 1.5m is recommended and will work best with other gear.
3.5. I2S RJ-45 output connector (single-ended signalling)
I2S is a more direct D/A interface than S/PDIF. It was developed by Philips when Philips
and Sony created the CD format and the S/PDIF interface specification. I2S is a three or
four-signal interface that includes clocks. All four signals are provided at 3.3V logic levels
at the Off-Ramp 5 output.
I2S is the native interface for most D/A chips. Therefore if one can drive I2S directly and
avoid S/PDIF translation, there is the opportunity to reduce jitter even more. Empirical
Audio standard I2S interface uses 4 signals and 4 returns and the RJ-45 connector. It is
compatible with I2S on several other manufacturers DACs, including Stello, Perpetual
Technologies and Northstar, as well as our own Overdrive DAC. Other manufacturers
DACs require an adapter cable to make the connection since they don’t all use RJ-45
and the pinouts are not compatible. A 1.5m cable length is recommended..
Make sure the I2S connectors are mated at both ends of the cable before
powering-on either the Off-Ramp 5 or the DAC. Likewise, power both down before
disconnecting the I2S cable.
For operation without I2S cable, make sure that the supplied terminator is plugged
into the I2S output jack.
3.6. I2S HDMI output connector (differential signaling)
I2S compatible with Wired for Sound DAC2, PS Audio Perfect Wave DAC and others.
Uses the HDMI connector, but is not compatible with HDMI signalling used for Home
Theater, DVD, Blu-ray and Television. A standard HDMI cable can be used, however
audiophile quality cables will perform better. 1.5m minimum cable length is
Make sure the I2S connectors are mated at both ends of the cable before
powering-on either the Off-Ramp 5 or the DAC. Likewise, power both down before
disconnecting the I2S cable.
4. Software
Software drivers must be loaded to support the USB interface for both PC and Mac before
connecting the USB cable. For operation on a PC, Kernel Streaming is recommended to
bypass Kmixer on XP machines and WASAPI on Vista and Win7 machines.
4.1. USB Drivers
Drivers are located on the included CDROM disk. Load the appropriate driver for your
machine and OS and execute it on the computer before powering the Off-Ramp 4 or
connecting the USB cable to the computer for the first time.
4.2. Player Software
For PC, the latest version of Foobar2000 is recommended as a player. Install this first.
For XP, a Kernel Streaming plug-in is included on the CDROM. Copy this plug-in to the
“components” folder under C:\Program Files\Foobar2000. Then start Foobar2000 and
select the File pull-down. Then select Preferences. In the Preferences window, go to
Playback – Output – select HiFace Kernel Streaming or Empirical Audio async 192.
With XP, the sample-rate will be selected automatically. With Vista and Win7, you must
change the sample-rate manually on the computer in control-panel/sounds and audio
For Mac, we recommend iTunes with software add-ons such as Amarra or Pure Vinyl to
improve audio quality and eliminated manual intervention to select sample-rates.
If you use iTunes alone, then select HiFace in Preferences/Audio and use Utilities/Midi
options to select the sample-rate. Using iTunes alone requires you to manually select
the sample-rate each time you change to playback of a different sample-rate.
5. Quick Start-up
5.1. Mac
• Put the supplied CDROM into your Mac and find the Mac driver folder.
• Open the folder and copy the driver software to your Mac hard disk.
• Execute the driver installation and follow the instructions.
• Power-on the Off-Ramp and connect the USB cable to the Mac and S/PDIF
digital coax cable to the DAC.
• Power on the DAC.
• Check in the Perferences/Sounds that you have HiFace or Empirical Audio
async 192 selected for output
• Start your music player application
• Check that both the red and yellow LEDs are off on the Off-Ramp
• Play a track or playlist using your player application
5.2. PC
Put the supplied CDROM into your PC and find the PC driver folder.
Open the folder and copy the correct driver software to your PC hard disk.
Execute the driver installation and follow the instructions.
Power-on the Off-Ramp and connect the USB cable to a USB 2.0 port on your
PC and S/PDIF digital coax cable to the DAC.
Power on the DAC.
Check in the Control Panel/Sounds and audio devices that you have HiFace or
Empirical Audio async 192 selected for output
Install Kernel Streaming in your player application
Start your music player application
Select Empirical Audio 192 async Kernel Streaming for output
Check that the yellow LED is off on the Off-Ramp
Play a track or playlist using your player application
The red LED should be off when playing music
6. Specifications
1. USB – async 24/192 max sample-rate
1. S/PDIF coax
3. I2S on RJ-45, Empirical Audio standard (3.3V)
4. I2S on HDMI, PS Audio standard (LVDS)
Jitter specs (cycle to cycle, standard clock):
S/PDIF coax output - <390psec total P-P jitter at all frequencies
I2S Clock outputs - <250psec total P-P jitter at all frequencies
7. Compatibility
The Off-Ramp 5 is designed to work with all DACs and SS receivers/processors. It works only in
PCM mode. To operate with higher sample-rates, the DAC must support 24-bit operation as well
as the higher sample-rate. USB 2.0 is required. Linux is not supported.
Sample-rates supported: 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz, 192kHz
1. Off-Ramp 5 with 2 standard clocks (except with Turboclock upgrade)
2. BNC to RCA adapter plug
3. 12VDC AC adapter
4. 5m USB cable
5. CDROM with drivers and other software
1. Turboclock
2. S/PDIF Hynes voltage regulator
3. HDMI Hynes voltage regulator
4. RCA output connector rather than BNC
5. Revelation Audio Labs Cryo-Silver Reference I2S cable
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