37.2 Latency and Monitoring
The term Zero Latency Monitoring has been introduced by RME in 1998 for the DIGI96 series of audio cards. It stands for the ability to
How much Zero is Zero?
From a technical view there is no zero. Even the analog
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
Sample frequency kHz | 44.1 | 48 | 88.2 | 96 | 176.4 | 192 |
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AD (43.2 x 1/fs) ms | 0.98 | 0.9 | 0.49 | 0.45 |
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AD (38.2 x 1/fs) ms |
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| 0.22 | 0.2 |
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DA (43.5 x 1/fs) ms | 0.99 | 0.9 | 0.49 | 0.45 | 0.25 | 0.23 |
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DA (28 x 1/fs) ms * | 0.63 | 0.58 | 0.32 | 0.29 | 0.16 | 0.15 |
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*The second DA values are valid for units built since around march 2005 (AK4396 instead of AK4395). The driver detects the version automatically and transmits the correct offsets.
Buffer Size (Latency)
Windows: This option found in the Settings dialog defines the size of the buffers for the audio data used in ASIO and GSIF (see chapter 13 and 14).
Mac OS X: The buffer size is defined within the application. Only some do not offer any setting. For example iTunes is fixed to 512 samples.
General: A setting of 64 samples at 44.1 kHz causes a latency of 1.5 ms, for record and play- back each. But when performing a digital loopback test no latency/offset can be detected. The reason is that the software naturally knows the size of the buffers, therefore is able to position the newly recorded data at a place equalling a
AD/DA Offset under ASIO and OS X: ASIO (Windows) and Core Audio (Mac OS X) allow for the signalling of an offset value to correct buffer independent delays, like AD- and
96 | User's Guide Fireface 800 © RME |