Basic audio programming

Basic audio programming

Iulian Şerbănoiu - March 2010

Contents

●Basic notions○ Sample ○ Sample rate○ Audio bit depth

●Example○ portaudio

●Other audio libraries●References

Basic notions - sample

Each square ( <fi> i=1..12 ) represents a sample

Basic notions - sample rate

Sample rate = number of samples in a secondgreater T -> smaller sample rate -> lower qualitysmaller T -> greater sample rate -> higher quality

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

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

Example - portaudio init/close stream

In portaudio, the stream is the primitive for sound processing Pa_Open(Default)Stream( .... );

Pa_CloseStream(createdStream);


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


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


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

ReferencesBasic 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/

Basic audio programming

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