Get sound wave from QAudioInput

[Robotechnic]

Hello,
I want to get a sound wave from QAudioInput like here:

This is a python code from here.
This code works bu I want to do that with c++.

Here is my code to do that (only for test purpose, I will clean and optimise it later):
code to get audio output

    auto io = this->audio->start();

    connect(io,&QIODevice::readyRead,[this,io]{

        QByteArray buff = io->readAll();
        int buffLenght = buff.length();
        if (buffLenght>0){
            this->processAudioFrame(buff.constData(),buffLenght);
        }
    });

code to convert audio QByteArray to list of numbers:

void Window::processAudioFrame(QByteArray data, int lenght){
    if(lenght > 0)
    {
         short* result = (short *)data.data();
                for (int  i=0; i < lenght/2; i++ )
                {
                    ui->soundView->pushSoundLevel(result[i]/32768.0);
                }
    }
}

and here in my custom widget the pushSoundLevel and repaintEvent methods:

void SoundWidget::pushSoundLevel(double level){
    buffer.push_back(level);
    buffer.pop_front();
    this->update();
}


void SoundWidget::paintEvent(QPaintEvent *event){
    QPainter p(this);
    QPolygonF soundWave;

    for (int x = 0; x<this->buffer.size(); x++){
        soundWave<<QPointF(x,(buffer.at(x)*0.2*this->height())+this->height()/2);
    }

    QRectF boundingRect = soundWave.boundingRect();
    QTransform t;
    t.scale(this->width()/boundingRect.width(),1);

    p.setTransform(t);
    p.drawPolyline(soundWave);
}

My QAudioInput's parameters are that:

    format.setSampleRate(11025);
    format.setChannelCount(1);
    format.setSampleSize(16);
    format.setSampleType(QAudioFormat::SignedInt);
    format.setByteOrder(QAudioFormat::LittleEndian);
    format.setCodec("audio/pcm");

And I have this result:

I think that my problem come from the QByteArray conversion but I don't know why.

I am on Arch linux with Qt 5.15.2.

Thanks for your help.

[jsulm]

@Robotechnic said in Get sound wave from QAudioInput:

for (int i=0; i < lenght/2; i++ )

I would say it should be

for (int  i=0; i < lenght; i+=2 )

[Robotechnic]

Ok thanks @jsulm but, unfortunatly, this solution doesn't work as espected

[jsulm]

@Robotechnic Just realised: result is already short*, so i+=2 is indeed wrong.

[Robotechnic]

I think my problem come from the range of the for loop because, when I play static note on a flute I got this graph:

And as you can see around garbage of random values, I have good wave
If someone know how to fix that thanks in advance
I have also removed

    QRectF boundingRect = soundWave.boundingRect();
    QTransform t;
    t.scale(this->width()/boundingRect.width(),1);
    p.setTransform(t);

because this create some problems

[Robotechnic]

I fixed my problem:

with a qDebug of lenght I have:

data.length()	lenght
136	2730
740	1364
1326	1366
414	1364
208	1366
458	1364

As you can see they are not the same so, with this code, my problem is fixed:

void Window::processAudioFrame(QByteArray data){
    const short* result = (short *)data.constData();


    for (int  i=0; i < data.length()/2; i ++ ){
        ui->soundView->pushSoundLevel(result[i]);
    }

}