IP Audio Delay
This page discusses the general concept of how Audio over IP works and why there is always an inherent delay/latency in Audio over IP devices - whoever makes them.
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Latency
The end-to-end latency of an Ethersound encoder and a Barix ES100spkr decoder heavily depends on the codec used.
VLSI based devices
On Exstreamer 100, Exstreamer 110 and Exstreamer 200 the end-to-end latency is approximately 57ms. This is caused by large internal buffers in the VLSI codec.
Micronas based devices
The internal buffers of the Micronas codec are much smaller which also positively affects the latency. The end-to-end-latency of the Exstreamer 1000, Annuncicom 100, Annuncicom 200 and Annuncicom 1000 is only about 6ms.
Latency measurements
Both latencies were measured in the below described test.
Test environment
The latency was measured with the following equipment:
- Digigiram ES220 as an input device
- another ES220 as a reference output device
- Exstreamer 100 as an output device (VLSI based device)
- Annuncicom 100 as an output device (Micronas based device)
- HP procurve 1700-8 switch where all devices were connected to
Both Barix devices were loaded with the version 00.03 of the Ethersound decoder module.
The input of the ES220 was fed with a 500Hz tone from a signal generator. The input, both output Barix devices as well as the reference ES220 device were monitored with an oscilloscope.
A trigger was set to capture the waveform after switching on the signal generator.
Test results
The below three diagrams show the results of the measurement. The top line (channel 4, green) is the clock source. Channels 1 (yellow), 2 (blue) and 3 (violet) are: the VLSI device (Exstreamer 100), the Micronas device (Annuncicom 100) and the reference ES220.
On the first diagram the 57.2ms latency of the VLSI decoder (Exstreamer 100) can be seen.
The second screen shot shows the end-to-end latency using a Micronas based device Annuncicom 100. The latency is significantly lower - only 6ms.
The last picture shows the end-to-end delay using the reference ES220 device. The latency is 1.44ms.
