Latency And Monitoring - RME Audio ADI-2 Pro User Manual

34.2 Latency and Monitoring

Preamp Mode
In Preamp mode the analog input signal is converted to digital, processed by the DSP, then
converted back to analog. An ADC and DAC have a specific delay caused by their internal over-
sampling and anti-alias filtering. This delay has been reduced significantly in the last years, and
is now so small that usually it is impossible to hear. The values of the AD and DA conversion
are shown in the table below. The total latency is around 11 samples higher due to the FPGA
and DSP exchanging data (22 samples at Quad Speed). At 44.1 kHz there are 23 samples
delay, equalling 0.5 ms. At 192 kHz total delay is 36 samples or 0.2 ms! That's not far from a
straight wire.
Low Latency
The ADI-2 Pro uses the latest top AD- and DA-converters with special low latency filters, offer-
ing exceptional signal to noise and distortion figures in combination with a super-fast conver-
sion. A delay of down to 5 samples had been unavailable a few years back. The exact delays
caused by the AD- and DA-conversion of the ADI-2 Pro converter chips are:
Sample rate kHz
AD (5 x 1/fs) ms
DA Sharp (6.25 x 1/fs) ms
DA Sharp (5.63 x 1/fs) ms
DA Slow (5.3 x 1/fs) ms
DA Slow (4.68 x 1/fs) ms
These values represent an important step in further reducing the latency in the computer-based
recording studio. The added latency - at least from AD- and DA-conversion - can simply be
ignored.
USB Recording and Playback
Class Compliant mode is not different to other formats. The transfer of data in/out of the com-
puter is done in form of buffers. The size of these buffers define the latency or delay that occurs
on the input and output path. The total delay from analog input to analog output, passing
through the computer and a DAW software, is called roundtrip latency. On a typical computer, a
round-trip latency of 5 to 10 ms can be expected.
Under Mac OS X Class Compliant works identical to standard audio. The latencies are there-
fore the same, and – as usual – defined within the DAW software by setting the desired buffer
size.
Under iOS Class Compliant is the only way to I/O audio at all, and usually provides similar per-
formance for different interfaces.
Under Windows RME provides the MADIface series driver to use the ADI-2 Pro like any other
RME audio interface, with the same spectacular performance, although being a Class Compli-
ant device. Both WDM and ASIO are available. Latency under ASIO mainly depends on the
buffer size set in the driver's Settings dialog.
44.1 48 96
0.11 0.10 0.06
0.14 0.13
0.06
0.12 0.11
0.05
User's Guide ADI-2 Pro © RME
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0.026
0.029
0.024
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