AVB Network Latency
All devices in an AVB network share the same time. This allows the sending device (talker) to specify the precise point of time when its audio samples should be played out at the receiver side (listener). This is achieved by adding an offset to the current time and sending the resulting timestamp with each sample transmitted. The timestamp is called "presentation time" and has nanosecond precision. For comparison, a single sample at 48 kHz has a duration of over 20800 ns.
The receiver compares the incoming presentation time of each sample to the current time and buffers the sample until the presentation time is has come.
The offset (maximum transit time) is specified by the AVB standard as 2 ms for class A traffic, which is enough time for the signal to pass through a very large network under full load with up to seven 100 MBit/s switches along the way. By default, most AVB products will use this offset. In smaller networks with less hops or 1 GBit/s link speed, the offset can be adjusted to lower values, such as 0.3 ms, 0.6 ms or 1 ms. In the event that the chosen offset is too low, the audio stream may experience drop-outs or distortion.
|The RME Digiface AVB shows the remaining offset ("input delay") for the first incoming stream, which is useful to verify that a shorter setting for the existing network can be used without risking dropouts.|
The M-32 AD Pro acts both as a talker with a specified offset of 2 ms, adjustable down to 0.3 ms, and as a listener - where the latency is configured by the talker.
|In AVB networks, the latency is always specified by the talker and guaranteed by the listener. This behavior is plug and play and does not require any user interaction or monitoring.|