[vorbis-dev] recent Vorbis, sound quality problems

[David Riley]

Segher Boessenkool wrote:
> 
> Hello all,
> 
> I'm having some problems with the sound quality of recent Vorbis.
> There is some kind of metallic echo/tremolo effect in the lower
> frequencies. This is on my iMac; haven't seen this problem on x86.
> If you need a sample, I can put one up somewhere, or mail it to
> someone with a good ftp server, preferably.
> 
> It could be caused by the iMac sound system doing surround sound,
> (Dolby Spatializer or something); I don't know if/how it can be
> turned off.

What player are you using?  I've noticed that ones closely based off the
decoder_example are prone to sending Sound Manager buffers that are way
too small (128 bytes).  This isn't a problem on the decoder_example,
since it's writing to a file, nor is it a problem on many architectures
where one writes directly to the sound hardware (or at least directly
into a DMA buffer).  On the Mac it's a problem because you need to
double-buffer the sound and sending Sound Manger lots of tiny little
buffers burdens it a lot.  I've noticed this problem in Unsanity Echo's
vorbis player; it's the same sound artifact my vorbis player was giving
before Monty pointed out my problem.  If you want an example of a Mac
player that's *very* basic but doesn't have that specific problem, try
<http://oscar.the-rileys.net/programming/vorbis/vorbis.tar.gz> or to
browse the main source file
<http://oscar.the-rileys.net/programming/vorbis/mac/macogg.c>.  It sends
buffers that are somewhat larger.

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