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Multi-Channel I/O

The ToolKit WvIn and WvOut classes (and their subclasses) support multi-channel audio data input and output. A set of interleaved audio samples representing a single time "slice" is referred to as a sample frame. At a sample rate of 44.1 kHz, a four-channel audio stream will have 44100 sample frames per second and a total of 176400 individual samples per second.

Most STK classes process single-sample data streams via their tick() function. In order to distinguish single-sample and sample frame calculations, the WvIn and WvOut classes implement both tick() and tickFrame() functions. The tickFrame() functions take or return a pointer to an array of audio data representing one or more sample frames. For single-channel streams, the tick() and tickFrame() functions produce equivalent results. When tick() is called for a multi-channel stream, however, the function either returns a sample frame average (WvIn) or writes a single sample argument to all channels (WvOut).

Multi-channel support for realtime audio input and output is dependent on the audio device(s) available on your system.

The following example demonstrates the use of the WvOut class for creating a four channel, 16-bit AIFF formatted audio file. We will use four sinewaves of different frequencies for the first two seconds and then a single sinewave for the last two seconds.

// foursine.cpp

#include "WaveLoop.h"
#include "WvOut.h"

int main()
{
  // Set the global sample rate before creating class instances.
  Stk::setSampleRate( 44100.0 );

  int i, j;
  WvOut *output = 0;
  WaveLoop *inputs[4];
  for ( i=0; i<4; i++ ) inputs[i] = 0;

  // Define and load the sine waves
  try {
    for ( i=0; i<4; i++ ) {
      inputs[i] = new WaveLoop( "rawwaves/sinewave.raw", TRUE );
      inputs[i]->setFrequency( 220.0 * (i+1) );
    }
  }
  catch (StkError &) {
    goto cleanup;
  }

  // Define and open a 16-bit, four-channel AIFF formatted output file
  try {
    output = new WvOut( "foursine.aif", 4, WvOut::WVOUT_AIF, Stk::STK_SINT16 );
  }
  catch (StkError &) {
    goto cleanup;
  }

  // Write two seconds of four sines to the output file
  MY_FLOAT frame[4];
  for ( j=0; j<88200; j++ ) {
    for ( i=0; i<4; i++ )
      frame[i] = inputs[i]->tick();

    output->tickFrame( frame );
  }

  // Now write the first sine to all four channels for two seconds
  for ( j=0; j<88200; j++ ) {
    output->tick( inputs[0]->tick() );
  }

 cleanup:
  for ( i=0; i<4; i++ ) delete inputs[i];
  delete output;

  return 0;
}

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The Synthesis ToolKit in C++ (STK)

©1995-2002 Perry R. Cook and Gary P. Scavone. All Rights Reserved.