Off-Ramp 4 User Manual
Empirical Audio Rev. 1.0
1. Function/Technology
The Off-Ramp 4 is a versatile hi-res compatible USB interface. The function of the Off-
Ramp 4 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 4 reduces jitter in the digital
data stream by re-clocking using local oscillators. The Off-Ramp 4 incorporates our best
low-jitter technology and includes an array of technical advantages over other devices on
the market, including:
•
Async USB, so expensive USB cable is not necessary
•
Inputs are re-clocked and S/PDIF and AES outputs are re-clocked again
•
External DC power source, allowing battery power
•
Separate input and output power regulation
•
High-quality discrete voltage regulation with Hynes regulator as option
•
Precision impedance-matched high slew-rate S/PDIF and AES/EBU output
•
Optimum clocking for best 24/176.4 and 24/192 performance
•
I2S output interface for lowest jitter to Empirical Audio DACs
•
Modular design to allow for clock, power and USB improvements and upgrades
These technical advantages allow the Off-Ramp 4 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 4 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 4.
The Off-Ramp 4 virtually eliminates the sibilance and harshness due to jitter, making your
digital playback closer to analog. The Off-Ramp 4 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 4 is to convert USB streaming audio format into S/
PDIF, AES/EBU or I2S formats and provide hardware interfaces in order to be compatible
