Qt 5.8 | Qt Multimedia | Spectrum Example | tonegenerator.cpp Example File

Qt 5.8.0 Reference Documentation

# tonegenerator.cpp Example File

multimedia/spectrum/app/tonegenerator.cpp

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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;
          }
      }