RME Audio ADI-2 Pro, User Manual

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User’s Guide ADI-2/4 Pro SE – v 1.0
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34.2 Latency and Monitoring
Preamp Mode
In Preamp mode the analog input signal is converted to digital, processed by the DSP, then con-
verted 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 24 samples delay,
equalling 0.5 ms. At 192 kHz total delay is 69 samples or 0.36 ms.
Low Latency
The ADI-2/4 Pro SE uses the latest top AD- and DA-converters with special low latency filters,
offering exceptional signal to noise and distortion figures in combination with a super-fast conver-
sion. The exact delays caused by the AD- and DA-conversion of the ADI-2/4 Pro SE converter
chips are:
Sample rate kHz 44.1 48 96 192
AD SD Sharp (3.25 x 1/fs) ms 0.07 0.067 0.039 0.017
AD SD Slow (2.12 x 1/fs) ms 0.05 0.04 0.022 0.011
DA SD Sharp (5.4 x 1/fs) ms 0.12 0.11 0.06 0.028
DA SD Slow (3.5 x 1/fs) ms 0.08 0.07 0.056 0.018
DA NOS (1 x 1/fs) ms 0.02 0.02 0.01 0.005
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 ig-
nored.
USB Recording and Playback
Class Compliant mode is not different to other formats. The transfer of data in/out of the computer
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
Round Trip Latency . On a typical computer, a RTL of 5
to 10 ms can be expected.
Under Mac OS X Class Compliant works identical to standard audio. The latencies are therefore
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-2/4 Pro SE like any
other RME audio interface, with the same spectacular performance, although being a Class Com-
pliant device. Both WDM and ASIO are available. Latency under ASIO mainly depends on the
buffer size set i
n the driver’s Settings dialog.
Typical RTL values at 44.1 kHz sample rate for Windows ASIO:
Buffer Size
RTL in samples / milliseconds
128 samples 323 samples, 7.32 ms
64 samples 195 samples, 4.42 ms
32 samples 131 samples, 2.97 ms