From:	"Damian Yerrick" <NOSP AT Musenet@pineight.8m.com>
Newsgroups:	comp.os.msdos.djgpp
References:	<Pine DOT BSF DOT 4 DOT 10 DOT 9912020027390 DOT 39597-100000 AT studenti DOT ing DOT unipi DOT it>
Subject:	Re: Sound stream corruption with Allegro?
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Organization:	Pin Eight Software <http://pineight.8m.com/>
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NNTP-Posting-Date:	Thu, 02 Dec 1999 05:35:39 GMT
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Date:	Thu, 02 Dec 1999 05:35:39 GMT
To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

"Luca Bisti" <s150405 AT studenti DOT ing DOT unipi DOT it> wrote in message
news:Pine DOT BSF DOT 4 DOT 10 DOT 9912020027390 DOT 39597-100000 AT studenti DOT ing DOT unipi DOT it...
> Hi Allegro gurus,
>
> I have the following problem with the Allegro audio stream routines: for
some reason that I haven't been able to find out myself, the sound samples
generated by my program are somewhat distorted by the Allegro play routines,
that is the music which comes out of the soundcard is a bit "scratchy". I
say that because I dump the same sample buffer to a WAV file just before
passing it to the free_audio_stream() function and the music recorded into
that WAV sounds perfectly (not distorted at all) when played back with any
other sound player (such as Windows' Media Player itself).

Coded with WinAPI. Uses native Windows.

>This "corruption" does not consist in noise clicks at regular intervals or
things like that, but it's rather like a continuos sample "cut" which seems
to reduce sound dynamics... sorry, I can't explain it in words :-)
>
> Just to clarify, the situation is the following:
>
> mix_samples(buffer, size); // generate some music samples
> write_wav(buffer, size); // write them to the WAV file, which will play
back clean music
> free_audio_stream(); // pass the buffer to Allegro, which plays it
slightly distorted
>
> I am using a single audio stream (with a single voice) which can be
mono/stereo and 8/16 bit. Depending on the voice mode set, I mix a sample of
the same type myself and then play it through that voice. I use my own
mixing routines because I need to do some postprocessing on the final result
and Allegro won't let me do that if I open several independent voices and
let it mix them. In all the four combinations, the result is always the
same. Note that the sound corruption is particularly evident only when
playing certain sounds, while in general it's hardly audible. Anyway, I'd
like to get rid of this problem, since I don't want a player of
waveform-dependant quality!
>
> The voice frequency is the same as the soundcard playback rate, centered
voice panning, max volume, and my samples have amplitude 64 (just to make
sure that clipping cannot occur). Nothing changes if I use signed or
unsigned samples, or if I allocate a mono/stereo - 8/16 bit voice. My
soundcard is a Creative SB 32.
>
> What could be wrong? Since the WAV data is clean, my suspect is that the
waveform is altered by Allegro's mixing code (volume tables and so on). If
so, how can I make sure that my buffer is passed directly to the DMA without
any further processing by the Allegro routines?

Happens to me under NESticle, loopyNES, any DOS
Allegro program, or for that matter any Sound Blaster
program that plays waves. Windows tends to fsck up
DMA because its timer's resolution is too low. What
happens when you run from M$-DOS mode?


Damian Yerrick

Windows. Who gives a ScanDisk?

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