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;
     }
 }
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