fast drawing in Qt

Hi to all,
I'm trying to write an audio editor with waveform visualizer.
The number of audio samples I have to draw is ~10E6 or more. This is the code where I draw them:

Code:

---

void WaveWidget::updateWave()
{
	int h = height();
	int w = width();
	// I need width and height here.
	// Also, I clear the cache at resize events
	QPixmap temp = QPixmap( w, h );
 
	QPainter p( &temp );
	p.setRenderHint( QPainter::Antialiasing );
	p.fillRect( temp.rect(), Qt::white );
 
	QPen pen( Qt::blue, 1 ); // blue solid line, 1 pixels wide
	p.setPen( pen );
	short* audio = reinterpret_cast<short*>(soundStream);
	for( unsigned int i = 0; i < numSamples; i++ )// numSamples very big (~10e6 or more)
	{
		int startY = maxHeight;
		for( int k = 0; k < channels; k++ )
		{
			short* value1 = audio + k;
			int x = i / ( numSamples / w); 
			int y = *value1 * maxHeight / 0x0000FFFF * 2;
			QLine line( x, startY, x, startY + y );
			p.drawLine(line);
			startY += increment;
		}
		audio += sampleSize;
	}
	m_waveCachePixmap = temp;
}

---

and the paintEvent

Code:

---

void WaveWidget::paintEvent( QPaintEvent* pe )
{
	// call updateWave only if necesary, if not I draw what is in cache
	if( m_waveCachePixmap.isNull() )
	{
		updateWave();
	}
 
	QPainter p( this );
	p.setRenderHint( QPainter::Antialiasing );
	p.drawPixmap( 0, 0, m_waveCachePixmap );
}

---

where waveWidget inherits from QWidget.
The problem is that the draw process is very slow as I have to draw more that 10 millions of lines. Is not a fast way do draw something? For example the same audio file in audacity is displayed very fast.

Best Regards