User manual

with DACs. The Off-Ramp 4 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 4. This clock provides the
timing for the dataflow from the computer source. This is the optimum way to achieve
low jitter.
The Off-Ramp 4 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 4 and your
DAC. This should be a high-quality S/PDIF coax, AES/EBU or I2S cable to minimize jitter.
1.3. Performance of different outputs
The three outputs all deliver world-class performance, however in highly resolving
systems some differences may be audible.
The I2S output delivers the lowest jitter, for those that have DACs with this type of input.
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.
For non-Empirical Audio DACs, we recommend using the S/PDIF output with a high-
quality S/PDIF coax cable, such as the Empirical Audio Bitmeister.
1.4. Internal clocks and clock quality
The Off-Ramp 4 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 of either one or both of the sample-
rate groups. One or two Ultraclocks or one or two Superclock4s can be added. Other
clock options may be offered in the future. These clock upgrades are not user-installable.