2 May
2007
2 May
'07
4:34 p.m.
Hi,
About a week ago, out of boredom, I started working on
little retro-styled '80s kind of video game, written
in a pretty simple-minded way with gnome, and the graphics
done just by using line drawing primitives. It was just
something to do, I didn't imagine it would amount to anything.
Well, it's turning out surprisingly well (not great, but
better than I was expecting.) So now I'm thinking to add
sound, but apart from some MIDI programming, I really haven't
done any audio programming before (unless you count some
Extended BASIC code on a ti99/4a back in the '80s -- and
nobody would count that.)
So, I found libao ( http://xiph.org/ao/doc/ ) which looks
nice and simple, and the sample program I tried
( http://xiph.org/ao/doc/ao_example.c ) worked right off
the bat, and the idea of synthesizing my own sounds by
constructing waveforms using sine waves is appealing for
a retro styled app like mine (though I have no experience
doing that and only a vague memory of trigonometry), but
I wonder about how to mix sound (add the waveforms, I guess)
and construct them on the fly (or trigger pre-computed
chunks of audio).
In the example code, it plays a one second chunk of audio
with one library call initiating the playback.
So, I imagine that for a game, in order to satisfy the
real-time-ish requirements, I'd instead construct maybe
1/10th or 1/20th second chunks, which would be queued up
in my program for playback, and whenever some event happens
which demands some sound be produced _right now_ (like the
user presses the "fire" button, and so needs some bleeping
laser gun sounds to be produced) I would then start adding
(arithmetic addition) laser-gun-waveform-data into whatever
chunks were already in the queue, and so out would come
the sound...
Does that seem like a reasonable approach?
By chopping the sound up into 1/10t or 1/20th second chunks,
am I apt to cause distortion of some kind?
Is there some other library I might be better off with?
(I looked at SDL, but it seems heavily tilted towards
graphics, and I already have the graphics stuff going alright
under just regular old gnome.)
I might also want to playback some ogg encoded files for maybe
prerecorded sound effects and music to be mixed
in with the synthesized sound effects. libao won't do that by itself, but
I think there are some other libs on xiph.org that do that, but
I'm not sure how well they'd accomodate mixing random bits of
sound in with them.
Saw this: http://www.underbit.com/products/mad/
fixed point mpeg decoder library... Not sure how
easy it'd be to mix in other sounds with its output.
Maybe just decode into memory buffer.
Anyway, just looking for suggestions, esp. if what
I've described so far seems wrong.
-- steve
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2 May
2 May
6:48 p.m.
New subject: Libraries for simple audio programming, libao, other options?
On 5/2/07, Stephen Cameron <smcameron(a)yahoo.com> wrote:
So, I found libao ( http://xiph.org/ao/doc/ ) which
looks
nice and simple, and the sample program I tried
( http://xiph.org/ao/doc/ao_example.c ) worked right off
the bat,
If you want real-time, then you'd better use a callback-based API.
PortAudio might be a good choice for your application:
http://www.portaudio.com/
and the idea of synthesizing my own sounds by
constructing waveforms using sine waves is appealing for
a retro styled app like mine (though I have no experience
doing that and only a vague memory of trigonometry), but
I wonder about how to mix sound (add the waveforms, I guess)
and construct them on the fly (or trigger pre-computed
chunks of audio).
Since you're just doing this for fun, you might opt to synthesize your
own sounds in real-time, but it would probably be more "sensible" to
synthesize them ahead of time. In this case, I suppose it really comes
down to your personal preference.
To answer your question about mixing: yes, you just add the waveforms.
You have to be sure to avoid clipping, so it can be a bit more
complicated than that, but that's the gist of it. An explanation of
how analog-emulation synthesis works is out of the scope of this
email, but I'm sure there's some literature you can find on the
subject. For my own part, I just trawled Wikipedia and gradually
assembled a picture of how it all works, but that's a rather
time-consuming option. Maybe someone else can recommend some
literature. :)
So, I imagine that for a game, in order to satisfy
the
real-time-ish requirements, I'd instead construct maybe
1/10th or 1/20th second chunks, which would be queued up
in my program for playback, and whenever some event happens
which demands some sound be produced _right now_ (like the
user presses the "fire" button, and so needs some bleeping
laser gun sounds to be produced) I would then start adding
(arithmetic addition) laser-gun-waveform-data into whatever
chunks were already in the queue, and so out would come
the sound...
I think that if you look at the way PortAudio works, you'll see that
this sort of "queueing" logic is taken care of for you by the library,
so you don't need to worry about it.
I might also want to playback some ogg encoded files
for maybe
prerecorded sound effects and music to be mixed
in with the synthesized sound effects. libao won't do that by itself, but
I think there are some other libs on xiph.org that do that, but
I'm not sure how well they'd accomodate mixing random bits of
sound in with them.
If you're going for the "retro" effect, you might actually consider
synthesizing the music in real-time from a MIDI-style score. :) If
you'd rather do it pre-recorded, however, the approach that you'll
take would be to find a decoder library, have it decode your music
into a memory buffer (probably streaming it somehow), and then mix
that into your own output buffer along with the sound effects.
Hope that helps!
11:51 p.m.
New subject: Libraries for simple audio programming, libao, other options?
--- nick thomas <jesuswaffle(a)gmail.com> wrote:
Yeah, I planned on doing it ahead of time, where possible.
The game already eats about 35% of a 2.1GHz Athlon, heh.
Yes, very much. Thanks.
-- steve
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On 5/2/07, Stephen Cameron <smcameron(a)yahoo.com>
wrote:
Ok, that looks cool.
So, I found libao ( http://xiph.org/ao/doc/ )
which looks
nice and simple, and the sample program I tried
( http://xiph.org/ao/doc/ao_example.c ) worked right off
the bat,
If you want real-time, then you'd better use a callback-based API.
PortAudio might be a good choice for your application:
http://www.portaudio.com/ and the idea of synthesizing my own sounds by
constructing waveforms using sine waves is appealing for
a retro styled app like mine (though I have no experience
doing that and only a vague memory of trigonometry), but
I wonder about how to mix sound (add the waveforms, I guess)
and construct them on the fly (or trigger pre-computed
chunks of audio).
Since you're just doing this for fun, you might opt to synthesize your
own sounds in real-time, but it would probably be more "sensible" to
synthesize them ahead of time. In this case, I suppose it really comes
down to your personal preference.
To answer your question about mixing: yes, you just add the waveforms.
You have to be sure to avoid clipping, so it can be a bit more
complicated than that, but that's the gist of it. An explanation of
how analog-emulation synthesis works is out of the scope of this
email, but I'm sure there's some literature you can find on the
subject. For my own part, I just trawled Wikipedia and gradually
assembled a picture of how it all works, but that's a rather
time-consuming option. Maybe someone else can recommend some
literature. :)
Hmm, no, I don't see that.
I see it has a callback where I have to feed it audio data
X samples at a time (where I get to define X), but I don't
see anything to help with mixing various audio sources.
I guess the callback to do that would look something like
this: (based on what I see here:
http://www.portaudio.com/trac/wiki/TutorialDir/WritingACallback )
/* I imagine sound_source_list to be a pointer to
array of various sound sources I want to mix,
passed to my callback in a cookie */
sound_source_list = (my_whatever *) callback_cookie;
/* "out" is ptr via which to feed portaudio interleaved
L and R audio data for playback */
out[0] = 0;
out[1] = 0;
new_num_sound_sources = num_sound_sources;
for (i=0;i<frames_per_buffer) {
for (j=0;j<num_sound_sources;j++) {
int pos = sound_source[j]->pos;
if (sound_source[j] == NULL)
continue;
out[0] += sound_source[j]->data[pos].left; /* left */
out[1] += sound_source[j]->data[pos].right; /* right */
sound_source[j]->pos++;
if sound_source[j]->pos = sound_source[j].maxpos; {
sound_source[j] = NULL;
if (j == num_sound_sources)
new_num_sound_sources--;
}
}
out += 2;
num_sound_sources = new_num_sound_sources;
}
Then, when the user presses some button that needs to make
noise, a new sound source just gets added to the sound_source
array, maybe like this:
/* Set up structure to hold index and pointer to laser sound data */
new_sound->data = laser_sound_data;
new_sound->pos = 0;
new_sound->maxpos = laser_sound_data_num_samples;
/* add it to sound_source list */
found = 0;
for (i=0;i<num_sound_sources;i++) {
if (sound_source[i] == NULL) {
sound_source[i] = new_sound;
found = i;
}
}
if (!found && num_sound_sources < MAX_SOUND_SOURCES)
sound_source[num_sound_sources++] = new_sound;
Does all that seem more or less about right?
Eh, I see a race in setting num_sound_sources. Hmmm.
Am I even close?
(Hope that wasn't so sketchy that it failed to be comprehesible.)
So, I imagine that for a game, in order to
satisfy the
real-time-ish requirements, I'd instead construct maybe
1/10th or 1/20th second chunks, which would be queued up
in my program for playback, and whenever some event happens
which demands some sound be produced _right now_ (like the
user presses the "fire" button, and so needs some bleeping
laser gun sounds to be produced) I would then start adding
(arithmetic addition) laser-gun-waveform-data into whatever
chunks were already in the queue, and so out would come
the sound...
I think that if you look at the way PortAudio works, you'll see that
this sort of "queueing" logic is taken care of for you by the library,
so you don't need to worry about it. I might also want to playback some ogg encoded
files for maybe
prerecorded sound effects and music to be mixed
in with the synthesized sound effects. libao won't do that by itself, but
I think there are some other libs on xiph.org that do that, but
I'm not sure how well they'd accomodate mixing random bits of
sound in with them.
If you're going for the "retro" effect, you might actually consider
synthesizing the music in real-time from a MIDI-style score. :) If
you'd rather do it pre-recorded, however, the approach that you'll
take would be to find a decoder library, have it decode your music
into a memory buffer (probably streaming it somehow), and then mix
that into your own output buffer along with the sound effects.
Hope that helps!
3 May
3 May
12:14 a.m.
New subject: Libraries for simple audio programming, libao, other options?
--- Stephen Cameron <smcameron(a)yahoo.com> wrote:
I think that if you look at the way PortAudio
works, you'll see that
this sort of "queueing" logic is taken care of for you by the library,
so you don't need to worry about it.
Hmm, no, I don't see that.
Oh yeah I do see it now, so, nevermind.
Looking at pa_multi_sine.c, I can see that
each stream can have multiple channels, and an example
of doing it interleaved and not interleaved.
So, portaudio looks like it's just what I needed.
Thanks.
-- steve
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--- nick thomas <jesuswaffle(a)gmail.com> wrote:
[...]
12:58 a.m.
New subject: Libraries for simple audio programming, libao, other options?
On 5/2/07, Stephen Cameron <smcameron(a)yahoo.com> wrote:
Oh yeah I do see it now, so, nevermind.
Looking at pa_multi_sine.c, I can see that
each stream can have multiple channels, and an example
of doing it interleaved and not interleaved.
So, portaudio looks like it's just what I needed.
Hmm, not quite on the mark. Multiple channels give you more speakers;
for one channel, you have mono, for two channels, you have stereo, for
7 channels, you have surround sound, etc. However, you were right on
the mark with your code sample in the previous email. Just integrate
that into your program, and you should have a working audio engine.
The only wrinkle is the race condition you noted when accessing the
sources list. In a normal situation, you'd obviously solve the problem
using locks, but that's not an option in this case, since the
PortAudio callback isn't allowed to do any potentially blocking
operations (such as acquiring a lock). You need to use some sort of
lock-free synchronization algorithm. I've never tackled that sort of
problem with PortAudio in particular, but you may look at this page
(from the creator of PortAudio) for some pointers:
http://www.audiomulch.com/~rossb/code/lockfree/
8 May
8 May
1:17 a.m.
New subject: Libraries for simple audio programming, libao, other options?
--- nick thomas <jesuswaffle(a)gmail.com> wrote:
On 5/2/07, Stephen Cameron <smcameron(a)yahoo.com>
wrote:
Yes this seems to be the case, I did it (much like) what I wrote
in the previous email, and it works.
In case anyone is curious how it turned out, I put my silly
game on sourceforge.
http://wordwarvi.sourceforge.net
Still a bit of a work in progress, but the sound's working,
and it seems to be working pretty dang well indeed, so
thanks for all the help.
Not sure how long it takes the tar.gz to propagate out
to all the mirrors, but cvs should work, if the mirrors
aren't yet. It's a bit of a big download, 22Mb.
-- steve
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Oh yeah I do see it now, so, nevermind.
Looking at pa_multi_sine.c, I can see that
each stream can have multiple channels, and an example
of doing it interleaved and not interleaved.
So, portaudio looks like it's just what I needed.
Hmm, not quite on the mark. Multiple channels give you more speakers;
for one channel, you have mono, for two channels, you have stereo, for
7 channels, you have surround sound, etc. However, you were right on
the mark with your code sample in the previous email. Just integrate
that into your program, and you should have a working audio engine. 
3 May
3 May
12:20 p.m.
New subject: Libraries for simple audio programming, libao, other options?
On Wed, May 02, 2007 at 11:31:41AM -0700, Stephen Cameron wrote:
Well, it's turning out surprisingly well (not
great, but
better than I was expecting.) So now I'm thinking to add
sound, but apart from some MIDI programming, I really haven't
done any audio programming before (unless you count some
Extended BASIC code on a ti99/4a back in the '80s -- and
nobody would count that.)
Another pretty easy way to do retro-style music and sound effects
would be to embed a mod player library, eg mikmod:
http://mikmod.raphnet.net/doc/libmikmod-3.1.10/docs/mikmod.html
You could then use a mod tracker for composing the game music.
Back in the early 90s there were some pretty cool games that used this
approach (StarCon2 anyone? ... holy crap, it's been open-sourced!
http://sc2.sourceforge.net/info.php )
--
Paul Winkler
http://www.slinkp.com
6201
days inactive
6206
days old
linux-audio-dev@lists.linuxaudio.org
6 comments
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