Re: FC4/x86_64 and ALSA: [long] noise and distortion

["Bryan J. Smith" <b.j.smith@ieee.org>]

"Bryan J. Smith" <b.j.smith@ieee.org> wrote:
> The more channels, the worse it gets.
> With more and more audio channeling, and the more
> bandwidth that is required.

I guess to put it simply ...

It wasn't long ago that titles used 8-bit or 16-bit audio at
11MHz with 4-8 voices, ranges to keep from saturating the I/O. 
In those days, you could even do ISA for even stereo and get away
with it to a point.

Today, we are pushing 64-256 voices at full 24-bit audio at 48MHz
or even 96MHz, in stereo, if not 5.1, and that is _uncompressed_
because the host is sending it to the audio chipset (which
doesn't have any intelligence).  Just the stream coming back to
the audio card for output can be over 10MBps (and even higher for
7.1), on a bus that is only 133MBps one-way _ideal_ (with no
contension).

That's not including any synthesis where there is a 2-4MB wave
table sample in main memory that I/O is going on.  It's that
"thrashing" over the I/O because there is *0* intelligence
on-board that is the problem.  A good "test" is to reduce the
quality of the output at the source application.  If it goes
away, it's the I/O bottleneck.

I'm sure part of ALSA's problem is that sound cards are ideally
configured (all channels) in Linux by default).  In Windows, it
typically defaults to 2-channel and lower settings (although it
depends on the installer, many are interactive).  And I'm sure
the "independently created" ALSA programs aren't as "tuned" as
the vendor's Windows drivers -- especially for its more "unified"
wavetable approach in the case of synthesis.



-- 
Bryan J. Smith                 mailto:b.j.smith@ieee.org
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