Re: [linux-audio-dev] RFC: API for audio across network - inter-host audio routing

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Subject: Re: [linux-audio-dev] RFC: API for audio across network - inter-host audio routing
From: Martijn Sipkema (msipkema_AT_sipkema-digital.com)
Date: Fri Jun 14 2002 - 22:14:26 EEST


> Going back to the issue of latency, it should be pointed out that while
> it might not be a big deal if your softsynth takes 25 ms to trigger,

It is unless you only use it with a sequencer.

> latency on the PCI bus is a big problem. If you can't get data from
> your HD (or RAM)

From memory I think. (is it possible for an audio card to read directly
from the hard disk??).

> to your soundcard fast enough
>, you _will_ hear dropouts
> in the audio. The more tracks, the higher the sampling rate, and the
> longer the wordlength, the greater the problem becomes. I think this is
> what people mostly are worried about when they talk about latency
> problems.

Yes, the PCI bus adds some extra latency. But that's not a problem.
The bandwidth I think will become a problem, but only with very large
numbers of channels high sample rate.

>A 25 ms dropout in the audiostream is quite noticeable and
> annoying. The discussions (which I did contribute to) on latency in
> acoustic instruments touched on the subject that trained performers of
> those instruments have learned to compensate for the inevitable delay
> between articulation and sound. Bus latency, however, is a completely
> different story....

If the bus has sufficient bandwidth there should be no dropouts. 25ms is
an extemely long period for the PCI bus. I'm not sure what the normal
buffer size for PCI transfers is, but this is in the order of a few hundred
usec worth of samples ,in the case of the audiowerk8 (philips saa7146)
a 24 Dword buffer per DMA channel (8 bytes per audio frame).

--martijn


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