RME M-16 AD [36/57] Latency and monitoring

User’s Guide M-32 AD © RME

16.3 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.

The exact delays of the M-32 AD are:

Sample rate kHz 44.1 48 88.2 96 176.4 192

AD (37 x 1/fs) ms 0.84 0.77 0.42 0.38

AD (9.5 x 1/fs) ms 0.054 0.05