- Qt 5.5
- Qt Multimedia
- Spectrum Example
- tonegenerator.cpp Example File
- Qt 5.5.1 Reference Documentation

# tonegenerator.cpp Example File

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;
        }
    }