ossaudiodev problem: sawtooth noise

[Peter Pearson]

On Thu, 22 Jan 2009 20:58:14 -0200, Gabriel Genellina wrote:
> En Mon, 19 Jan 2009 21:57:04 -0200, Peter Pearson  
><ppearson at nowhere.invalid> escribió:
>
>> The following code uses ossaudiodev to read 1000 values from
>> my sound card at a rate of 12,000 samples per second:
>>
>> When I select a sample rate that is not a power of 2 times
>> 3000 samples/second, a strong and very regular sawtooth is
>> superimposed on the signal.  At some sampling frequencies,
>> it appears as a rising sawtooth, and at other sampling
>> frequencies it is a declining sawtooth, so I'm presumably
>> lost in some aliasing wilderness.  As best I can tell,
>> it's a 48 KHz sawtooth.
>
> That could be a hardware and/or driver limitation. By example, an  
> AC97-compliant chipset may provide a fixed rate of 48000 samples/second --  
> any sample rate conversion must be done by other means, if possible at all.

Oh!  As a matter of fact, my "soundcard" *is* AC97-compliant
("VT8233/A/8235/8237", according to Sysinfo).  So . . . this
sawtooth might result from some software, somewhere in the bucket
brigade between me and the hardware, attempting to perform
sample-rate conversion?  The 48 KHz coincidence seems very
significant.

Thanks.

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