10 Oct
2003
10 Oct
'03
1:59 p.m.
-------- directBOX Reply ---------------
From: paul(a)linuxaudiosystems.com
To : linux-audio-dev(a)music.columbia.edu
Date: 10.10.2003 17:37:43
Hello !
I've read somewhere that it is not possible that threads write different data to /
dev/dsp.
But how does Cheesetracker, for example, make it then?
i don't how cheesetracker does it, but it requires user-space
synchronization (e.g. pthread_mutex_(un)lock). with ALSA, you don't
need to to do this - any thread can write to the device at any
time. that's the theory, at least. in general, its probably a bad
design to be doing that, much like it is for GUI programming, where
its better to have a single thread mediate between the "device" and
the rest of the program.
------------------
But well, If I synthize ( ? spelling) two signals and want to send them at the same time
to the device, my first idea'd be:
1.) Open /dev/dsp, maybe O_NONBLOCK | O_WRONLY
2.) thread
3.) two threads calculate the both signals
4.) sync them
5.) two threads write their signals to /dev/dsp
6.) threads close
certainly some of this. I mean mp3blaster, for example, have several pids while playing
audio streams, and it is basicly OSS-programming and not alsa.
Am I so wrong ? ;)
Sascha Retzki
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10 Oct
10 Oct
2:38 p.m.
New subject: [linux-audio-dev] Oss & threading -- is it possible
But well, If I synthize ( ? spelling) two signals and
want to send them at th
e same time
to the device, my first idea'd be:
1.) Open /dev/dsp, maybe O_NONBLOCK | O_WRONLY
2.) thread
3.) two threads calculate the both signals
4.) sync them
5.) two threads write their signals to /dev/dsp
6.) threads close
certainly some of this. I mean mp3blaster, for example, have several pids whil
e playing audio streams, and it is basicly OSS-programming and not alsa.
Am I so wrong ? ;)
you're completely wrong :)
you need to additively mix your two signals. writing them to DSP
orders them sequentially in time. it doesn't mix them.
6:30 p.m.
New subject: [linux-audio-dev] Oss & threading -- is it possible
On Fri, 2003-10-10 at 19:28, Paul Davis wrote:
you need to additively mix your two signals. writing
them to DSP
orders them sequentially in time. it doesn't mix them.
The commercial OSS driver does mixing and samplerate conversion.
--
Jussi Laako <jussi.laako(a)pp.inet.fi>
6:50 p.m.
New subject: [linux-audio-dev] Oss & threading -- is it possible
On Fri, 2003-10-10 at 19:28, Paul Davis wrote:
not of two sequential read(2) calls. please.
you need to additively mix your two signals.
writing them to DSP
orders them sequentially in time. it doesn't mix them.
The commercial OSS driver does mixing and samplerate conversion. 
6:58 p.m.
New subject: [linux-audio-dev] Oss & threading -- is it possible
On Fri, Oct 10, 2003 at 11:14:17PM +0300, Jussi Laako wrote:
On Fri, 2003-10-10 at 19:28, Paul Davis wrote:
OSS is the most disgusting API I have ever seen. For that reason alone, I
don't want to use it. I have this thing about paying attention to details,
and the OSS API, well, doesn't.
--
Notice that as computers are becoming easier and easier to use,
suddenly there's a big market for "Dummies" books. Cause and effect,
or merely an ironic juxtaposition of unrelated facts?
you need to additively mix your two signals.
writing them to DSP
orders them sequentially in time. it doesn't mix them.
The commercial OSS driver does mixing and samplerate conversion. 
3:21 p.m.
New subject: [linux-audio-dev] Oss & threading -- is it possible
On Friday 10 October 2003 17.41, hexe_2003(a)directbox.com wrote:
[...]
But well, If I synthize ( ? spelling) two signals and
want to send
them at the same time to the device, my first idea'd be:
1.) Open /dev/dsp, maybe O_NONBLOCK | O_WRONLY
2.) thread
3.) two threads calculate the both signals
4.) sync them
5.) two threads write their signals to /dev/dsp
6.) threads close
certainly some of this. I mean mp3blaster, for example, have
several pids while playing audio streams, and it is basicly
OSS-programming and not alsa.
Am I so wrong ? ;)
Yep! ;-)
Synths, trackers, games and other "polyphonic things" at some point
mix everything into a single stream that is sent to the audio device.
In general, all audio processing is done in a single thread, but in
some cases, it can be pretty hard to get the processing deterministic
enough that it can run in the audio thread without causing drop-outs.
This is especially troublesome if you need low latency, as in games
and other interactive applications.
This is probably why mp3blaster is using multiple threads; one for
each mp3 stream (decoding into raw audio data) and one for mixing and
output. There is most probably substantial buffering between the
decoding threads and the mixer thread, as this would allow solid
playback with less buffering (ie less laggy mixing controls) between
the mixer and the audio device.
//David Olofson - Programmer, Composer, Open Source Advocate
.- Audiality -----------------------------------------------.
| Free/Open Source audio engine for games and multimedia. |
| MIDI, modular synthesis, real time effects, scripting,... |
`-----------------------------------> http://audiality.org -'
--- http://olofson.net --- http://www.reologica.se ---
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5 comments
5 participants
participants (5)
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David Olofson -
hexe_2003＠directbox.com -
Jussi Laako -
Paul Davis -
Tim Hockin