Qt Reference Documentation

# tonegenerator.cpp Example File

demos/spectrum/app/tonegenerator.cpp

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     #include "spectrum.h"
     #include "utils.h"
     #include <QByteArray>
     #include <QtMultimedia/QAudioFormat>
     #include <QtCore/qmath.h>
     #include <QtCore/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.channels() * 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.frequency();

         // 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.channels(); ++i) {
                 qToLittleEndian<qint16>(value, ptr);
                 ptr += channelBytes;
                 length -= channelBytes;
             }

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