- Qt 5.3
- Qt Multimedia
- Spectrum Example
- spectrumanalyser.cpp Example File
- Qt 5.3.2 Reference Documentation

# spectrumanalyser.cpp Example File

spectrum/app/spectrumanalyser.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
    ** Contact: http://www.qt-project.org/legal
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
    ** You may use this file under the terms of the BSD license as follows:
    **
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    **     of its contributors may be used to endorse or promote products derived
    **     from this software without specific prior written permission.
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    #include "spectrumanalyser.h"
    #include "utils.h"
    #include "fftreal_wrapper.h"

    #include <qmath.h>
    #include <qmetatype.h>
    #include <QAudioFormat>
    #include <QThread>

    SpectrumAnalyserThread::SpectrumAnalyserThread(QObject *parent)
        :   QObject(parent)
    #ifndef DISABLE_FFT
        ,   m_fft(new FFTRealWrapper)
    #endif
        ,   m_numSamples(SpectrumLengthSamples)
        ,   m_windowFunction(DefaultWindowFunction)
        ,   m_window(SpectrumLengthSamples, 0.0)
        ,   m_input(SpectrumLengthSamples, 0.0)
        ,   m_output(SpectrumLengthSamples, 0.0)
        ,   m_spectrum(SpectrumLengthSamples)
    #ifdef SPECTRUM_ANALYSER_SEPARATE_THREAD
        ,   m_thread(new QThread(this))
    #endif
    {
    #ifdef SPECTRUM_ANALYSER_SEPARATE_THREAD
        // moveToThread() cannot be called on a QObject with a parent
        setParent(0);
        moveToThread(m_thread);
        m_thread->start();
    #endif
        calculateWindow();
    }

    SpectrumAnalyserThread::~SpectrumAnalyserThread()
    {
    #ifndef DISABLE_FFT
        delete m_fft;
    #endif
    }

    void SpectrumAnalyserThread::setWindowFunction(WindowFunction type)
    {
        m_windowFunction = type;
        calculateWindow();
    }

    void SpectrumAnalyserThread::calculateWindow()
    {
        for (int i=0; i<m_numSamples; ++i) {
            DataType x = 0.0;

            switch (m_windowFunction) {
            case NoWindow:
                x = 1.0;
                break;
            case HannWindow:
                x = 0.5 * (1 - qCos((2 * M_PI * i) / (m_numSamples - 1)));
                break;
            default:
                Q_ASSERT(false);
            }

            m_window[i] = x;
        }
    }

    void SpectrumAnalyserThread::calculateSpectrum(const QByteArray &buffer,
                                                    int inputFrequency,
                                                    int bytesPerSample)
    {
    #ifndef DISABLE_FFT
        Q_ASSERT(buffer.size() == m_numSamples * bytesPerSample);

        // Initialize data array
        const char *ptr = buffer.constData();
        for (int i=0; i<m_numSamples; ++i) {
            const qint16 pcmSample = *reinterpret_cast<const qint16*>(ptr);
            // Scale down to range [-1.0, 1.0]
            const DataType realSample = pcmToReal(pcmSample);
            const DataType windowedSample = realSample * m_window[i];
            m_input[i] = windowedSample;
            ptr += bytesPerSample;
        }

        // Calculate the FFT
        m_fft->calculateFFT(m_output.data(), m_input.data());

        // Analyze output to obtain amplitude and phase for each frequency
        for (int i=2; i<=m_numSamples/2; ++i) {
            // Calculate frequency of this complex sample
            m_spectrum[i].frequency = qreal(i * inputFrequency) / (m_numSamples);

            const qreal real = m_output[i];
            qreal imag = 0.0;
            if (i>0 && i<m_numSamples/2)
                imag = m_output[m_numSamples/2 + i];

            const qreal magnitude = sqrt(real*real + imag*imag);
            qreal amplitude = SpectrumAnalyserMultiplier * log(magnitude);

            // Bound amplitude to [0.0, 1.0]
            m_spectrum[i].clipped = (amplitude > 1.0);
            amplitude = qMax(qreal(0.0), amplitude);
            amplitude = qMin(qreal(1.0), amplitude);
            m_spectrum[i].amplitude = amplitude;
        }
    #endif

        emit calculationComplete(m_spectrum);
    }

    //=============================================================================
    // SpectrumAnalyser
    //=============================================================================

    SpectrumAnalyser::SpectrumAnalyser(QObject *parent)
        :   QObject(parent)
        ,   m_thread(new SpectrumAnalyserThread(this))
        ,   m_state(Idle)
    #ifdef DUMP_SPECTRUMANALYSER
        ,   m_count(0)
    #endif
    {
        CHECKED_CONNECT(m_thread, SIGNAL(calculationComplete(FrequencySpectrum)),
                        this, SLOT(calculationComplete(FrequencySpectrum)));
    }

    SpectrumAnalyser::~SpectrumAnalyser()
    {

    }

    #ifdef DUMP_SPECTRUMANALYSER
    void SpectrumAnalyser::setOutputPath(const QString &outputDir)
    {
        m_outputDir.setPath(outputDir);
        m_textFile.setFileName(m_outputDir.filePath("spectrum.txt"));
        m_textFile.open(QIODevice::WriteOnly | QIODevice::Text);
        m_textStream.setDevice(&m_textFile);
    }
    #endif

    //-----------------------------------------------------------------------------
    // Public functions
    //-----------------------------------------------------------------------------

    void SpectrumAnalyser::setWindowFunction(WindowFunction type)
    {
        const bool b = QMetaObject::invokeMethod(m_thread, "setWindowFunction",
                                  Qt::AutoConnection,
                                  Q_ARG(WindowFunction, type));
        Q_ASSERT(b);
        Q_UNUSED(b) // suppress warnings in release builds
    }

    void SpectrumAnalyser::calculate(const QByteArray &buffer,
                             const QAudioFormat &format)
    {
        // QThread::currentThread is marked 'for internal use only', but
        // we're only using it for debug output here, so it's probably OK :)
        SPECTRUMANALYSER_DEBUG << "SpectrumAnalyser::calculate"
                               << QThread::currentThread()
                               << "state" << m_state;

        if (isReady()) {
            Q_ASSERT(isPCMS16LE(format));

            const int bytesPerSample = format.sampleSize() * format.channelCount() / 8;

    #ifdef DUMP_SPECTRUMANALYSER
            m_count++;
            const QString pcmFileName = m_outputDir.filePath(QString("spectrum_%1.pcm").arg(m_count, 4, 10, QChar('0')));
            QFile pcmFile(pcmFileName);
            pcmFile.open(QIODevice::WriteOnly);
            const int bufferLength = m_numSamples * bytesPerSample;
            pcmFile.write(buffer, bufferLength);

            m_textStream << "TimeDomain " << m_count << "\n";
            const qint16* input = reinterpret_cast<const qint16*>(buffer);
            for (int i=0; i<m_numSamples; ++i) {
                m_textStream << i << "\t" << *input << "\n";
                input += format.channels();
            }
    #endif

            m_state = Busy;

            // Invoke SpectrumAnalyserThread::calculateSpectrum using QMetaObject.  If
            // m_thread is in a different thread from the current thread, the
            // calculation will be done in the child thread.
            // Once the calculation is finished, a calculationChanged signal will be
            // emitted by m_thread.
            const bool b = QMetaObject::invokeMethod(m_thread, "calculateSpectrum",
                                      Qt::AutoConnection,
                                      Q_ARG(QByteArray, buffer),
                                      Q_ARG(int, format.sampleRate()),
                                      Q_ARG(int, bytesPerSample));
            Q_ASSERT(b);
            Q_UNUSED(b) // suppress warnings in release builds

    #ifdef DUMP_SPECTRUMANALYSER
            m_textStream << "FrequencySpectrum " << m_count << "\n";
            FrequencySpectrum::const_iterator x = m_spectrum.begin();
            for (int i=0; i<m_numSamples; ++i, ++x)
                m_textStream << i << "\t"
                             << x->frequency << "\t"
                             << x->amplitude<< "\t"
                             << x->phase << "\n";
    #endif
        }
    }

    bool SpectrumAnalyser::isReady() const
    {
        return (Idle == m_state);
    }

    void SpectrumAnalyser::cancelCalculation()
    {
        if (Busy == m_state)
            m_state = Cancelled;
    }

    //-----------------------------------------------------------------------------
    // Private slots
    //-----------------------------------------------------------------------------

    void SpectrumAnalyser::calculationComplete(const FrequencySpectrum &spectrum)
    {
        Q_ASSERT(Idle != m_state);
        if (Busy == m_state)
            emit spectrumChanged(spectrum);
        m_state = Idle;
    }