linux-kernel - Re: Possible bug, with extreme low latency audio.

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Message-ID: <4D6DF1B2.2010500@ladisch.de>
Date:	Wed, 02 Mar 2011 08:28:50 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Uwaysi Bin Kareem <uwaysi.bin.kareem@...adoxuncreated.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Possible bug, with extreme low latency audio.

Uwaysi Bin Kareem wrote:
> The other is a firewire device (Konnekt24d using FFADO, running on the old
> firewire stack).
> The firewire device actually plays nicely without much buffer underruns
> down to 0.363 ms latency (8x2 @ 44.1k).

FireWire packets are sent every 125 µs; for audio, every packet contains
either zero or eight samples, and the proportion of data and no-data
packets is adjusted so that the overall rate is 44100 samples per
second.  So 8x2 is the theoretical minimum.

> However it seems to choke at 8x2 @ 96k.

At sample rates above 48 kHz, there are 16 samples per packet (and above
96 kHz, 32).  It is not possible to use 8x2 at 96 kHz, and FFADO should
not have allowed you to try it; please file a bug there:
<http://subversion.ffado.org/report> (requires a login).

Regards,
Clemens
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