tonegenerator.cpp Example File

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  #include "spectrum.h"
  #include "utils.h"
  #include <QByteArray>
  #include <QAudioFormat>
  #include <qmath.h>
  #include <qendian.h>

  void generateTone(const SweptTone &tone, const QAudioFormat &format, QByteArray &buffer)
  {
      Q_ASSERT(isPCMS16LE(format));

      const int channelBytes = format.sampleSize() / 8;
      const int sampleBytes = format.channelCount() * channelBytes;
      int length = buffer.size();
      const int numSamples = buffer.size() / sampleBytes;

      Q_ASSERT(length % sampleBytes == 0);
      Q_UNUSED(sampleBytes) // suppress warning in release builds

      unsigned char *ptr = reinterpret_cast<unsigned char *>(buffer.data());

      qreal phase = 0.0;

      const qreal d = 2 * M_PI / format.sampleRate();

      // We can't generate a zero-frequency sine wave
      const qreal startFreq = tone.startFreq ? tone.startFreq : 1.0;

      // Amount by which phase increases on each sample
      qreal phaseStep = d * startFreq;

      // Amount by which phaseStep increases on each sample
      // If this is non-zero, the output is a frequency-swept tone
      const qreal phaseStepStep = d * (tone.endFreq - startFreq) / numSamples;

      while (length) {
          const qreal x = tone.amplitude * qSin(phase);
          const qint16 value = realToPcm(x);
          for (int i=0; i<format.channelCount(); ++i) {
              qToLittleEndian<qint16>(value, ptr);
              ptr += channelBytes;
              length -= channelBytes;
          }

          phase += phaseStep;
          while (phase > 2 * M_PI)
              phase -= 2 * M_PI;
          phaseStep += phaseStepStep;
      }
  }