[NOOB] Layering multiple AIFFs in PCM format?
[NOOB] Layering multiple AIFFs in PCM format?
- Subject: [NOOB] Layering multiple AIFFs in PCM format?
- From: Quinn Taylor <email@hidden>
- Date: Thu, 11 Aug 2005 23:36:47 -0600
Hello, this is my first post on the list.
In an attempt to augment my current CS schooling which is highly Mac-
anemic, I'm working on my first pure Cocoa + ObjC project, which is
turning out to be much more ambitious than I first thought. The
program is a metronome called "Beat Doctor", similar to several
already in existence, but using CoreAudio directly rather than
NSSound or QuickTime. To get an idea of how it will work, please
refer to my website. (At the moment, the interface is essentially
complete, but the actual metronome function is extremely crude.) If
seeing the source will help, I can make it available as well.
http://homepage.mac.com/quinntaylor/software/
Basically, I want to composite as many as 5 source sounds (for
various subdivisions) together in a repeating pattern. The user will
be able to control the volume/muting of each individual sound, as
well as the master volume. The interval between these sounds is
determined by the tempo selected.
My goals/guidelines include the following:
- Make the code processor-independent.
- Blend sound from source AIFFs overtop of one another (at quicker
tempos).
- Cache the repeating pattern in PCM format, facilitating AIFF export
in the future.
- Cache the pattern in blocks of either 1 beat or 1 measure. (Improve
accuracy, reduce latency)
- Cause the pattern to be re-cached when the tempo or volumes are
changed while playing.
- Loop playback of this pattern while Play is enabled; halt abruptly
when playback is stopped.
I also need guidance in creating a high-priority thread for Core
Audio I/O so I don't have latency in creating the pattern cache or in
playback. So far I have looked at PlayBufferedSoundFile, which looks
moderately useful, but utilizes Mach calls for VM management. I've
also looked at the Sinewave demo, as well as OmniSoundExample (which
looks very promising) but haven't picked up exactly what I need.
I'm not familiar enough with Core Audio to know if this is the type
of thing that should be an Audio Unit bundle, or just straight code
inside my Cocoa app. Also, although my code is in Objective-C, I have
no aversion to using C calls for Core Audio. (I prefer to avoid
anything in C++.)
I know this is a huge load of basic questions. Thanks in advance for
any help you can give me in this regard!
- Quinn Taylor
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