Audio programming basic concepts: sample sample rate bit depth Audio programming libraries: portaudio rtaudio openal

1. Basic audio programming
Iulian Şerbănoiu - March 2010

2. Contents
●Basic notions
○Sample
○Sample rate
○Audio bit depth
●Example
○portaudio
●Other audio libraries
●References

3. Basic notions - sample
Each square ( <fi
> i=1..12
) represents a sample

4. Basic notions - sample rate
Sample rate = number of samples in a second
greater T -> smaller sample rate -> lower quality
smaller T -> greater sample rate -> higher quality

5. Basic notions - audio bit depth
Bit depth = number of bits in each sample
Common bit depths
●8 bit (signed/unsigned)
●16 bit (signed) - CD quality
●32 bit integer (signed)
●32 bit float (values ranging from -1 to 1)
Greater bit depth -> better sound quality -> more space needed

6. Example - portaudio (init/terminate)
Tipical portaudio usage:
Pa_Initialize();
...
DoMyPortaudioSoundOperations();
...
Pa_Terminate();
hg clone http://minvg.hg.sourceforge.net:8000/hgroot/minvg; cd minvg/trunk/PortaudioSoundPlayer

7. Example - portaudio init/close stream
In portaudio, the stream is the primitive for sound
processing
Pa_Open(Default)Stream(
....
);
Pa_CloseStream(createdStream);
hg clone http://minvg.hg.sourceforge.net:8000/hgroot/minvg; cd minvg/trunk/PortaudioSoundPlayer

8. Example - portaudio stream parameters
The stream creation function receives the following
parameters:
●number of Input/Output channels
●sample rate, bit depth
●processing callback and callback buffer size
●user data that can be passed to the callback
hg clone http://minvg.hg.sourceforge.net:8000/hgroot/minvg; cd minvg/trunk/PortaudioSoundPlayer

9. Example - portaudio callback
The callback is (asynchronously!) called periodically when:
●new input data arrived (when recording)
●new output data requested
int Callback(const void *input, void *output, ... );
Return values:
●paComplete - to end playing/recording after this call
●paContinue - to continue playing/recording
●paAbort - to end playing/recording ASAP
hg clone http://minvg.hg.sourceforge.net:8000/hgroot/minvg; cd minvg/trunk/PortaudioSoundPlayer

10. Other audio libraries
●RtAudio
○similar to portaudio (callback mechanism)
○object oriented design (C++)
●libsdl (audio component)
○similar to portaudio (callback mechanism)
○game development oriented
●OpenAL
○API similar to OpenGL
○higher level interface (compared to portaudio)
○game development oriented

11. References
Basic information
http://en.wikipedia.org/wiki/Sample_%28signal%2
http://www.tweakheadz.com/16_vs_24_bit_audio.htm
http://en.wikipedia.org/wiki/Sampling_rate
http://en.wikipedia.org/wiki/Audio_bit_depth
Audio libraries
http://www.music.mcgill.ca/~gary/rtaudio/
http://connect.creativelabs.com/openal
http://www.portaudio.com/
http://www.libsdl.org/
General information
http://www.dspguide.com/