RME Audio ADI-8 DS, Руководство пользователя

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User’s Guide ADI-8 DS
© RME
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13.3 Latency and Monitoring
The term Zero Latency Monitoring has been introduced by RME in 1998 for the DIGI96 series
and describes the ability to pass-through the computer's input signal at the interface directly to
the output. Since then, the idea behind has become one of the most important features of mod-
ern hard disk recording. In the year 2000, RME published two ground-breaking Tech Infos on
the topics
Low Latency Background , which are still up-to-date: Monitoring, ZLM and ASIO , and
Buffer and Latency Jitter , found on the RME website.
How much Zero is Zero?
From a technical view there is no zero. Even the analog pass-through is subject to phase er-
rors, equalling a delay between input and output. However, delays below certain values can
subjectively be claimed to be a zero-latency. This applies to analog routing and mixing, and in
our opinion also to RME's Zero Latency Monitoring. RME's digital receiver's buffer and the out-
put via the transmitter cause a typical delay of 3 samples. At 44.1 kHz this equals about 68 µs
(0.000068 s), at 192 kHz only 15 µs.
Oversampling
While the delays of digital interfaces can be disregarded altogether, the analog inputs and out-
puts do cause a significant delay. Modern converter chips operate with 64 or 128 times over-
sampling plus digital filtering, in order to move the error-prone analog filters away from the au-
dible frequency range as far as possible. This typically generates a delay of about 40 samples,
equalling one millisecond. A playback and re-record of the same signal via DA and AD (loop-
back) then causes an offset of the newly recorded track of about 2 ms.
Low Latency!
The ADI-8 DS uses the latest top AD- and DA-converters with special low latency filters, offer-
ing exceptional Signal to Noise and distortion figures and a super-fast conversion. 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-8 DS Mk III are:
Sample frequency kHz 44.1 48 88.2 96 176.4 192
AD (12.6 x 1/fs) ms 0.28 0.26
AD (12.6 x 1/fs) ms 0.14 0.13
AD (9.8 x 1/fs) ms 0.055 0.05
DA (10 x 1/fs) ms 0.22 0.2
DA (5 x 1/fs) ms 0.056 0.052
DA (5 x 1/fs) ms 0.028 0.026
These values are less than a quarter of those available from even much more expensive de-
vices. They represent an important step in further reducing the latency in the computer-based
recording studio. At Double Speed and Quad Speed the added latency can simply be ignored.
In short: the ADI-8 DS turns 'analog digital monitoring' into real analog-style monitoring.