Problems with layout

[franco.amato]

Hi I would layout some widget inside my class derived from QFrame.
This is the interface:

class PanelInfo : public QFrame
{
	Q_OBJECT
public:
	PanelInfo(QWidget* parent);
	~PanelInfo();
 
public slots:
	void panValueChanged(int);
	void volValueChanged(int);
 
protected:
private:
	QLabel* m_durationLabel;
	QLabel* m_channelsLabel;
	QLabel* m_freqLabel;
	QLabel* m_bitsLabel;
 
	QSlider* m_panSlider;
	QSlider* m_volSlider;
 
	QDoubleSpinBox* m_freqControl;
};

class PanelInfo : public QFrame
{
	Q_OBJECT
public:
	PanelInfo(QWidget* parent);
	~PanelInfo();

public slots:
	void panValueChanged(int);
	void volValueChanged(int);

protected:
private:
	QLabel* m_durationLabel;
	QLabel* m_channelsLabel;
	QLabel* m_freqLabel;
	QLabel* m_bitsLabel;

	QSlider* m_panSlider;
	QSlider* m_volSlider;

	QDoubleSpinBox* m_freqControl;
};

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In the ctor I would layout the widget but the result is not the expected:

PanelInfo::PanelInfo(QWidget* parent /* = 0 */ )
: QFrame(parent)
{
	setFrameStyle( QFrame::Box | QFrame::Raised );
 
        setMinimumSize( QSize(120, 240) );
	setSizePolicy( QSizePolicy::Fixed, QSizePolicy::Fixed );
 
	/* labels */
	m_durationLabel = new QLabel("DURATION");
	m_channelsLabel = new QLabel("CHANNELS");
	m_freqLabel = new QLabel("FREQ");
	m_bitsLabel = new QLabel("BITS");
 
	QVBoxLayout* ll = new QVBoxLayout();
	ll->setContentsMargins(0, 0, 0, 0);
        ll->setSpacing(0); //<---doesn't work in my case
	ll->addWidget( m_durationLabel );
	ll->addWidget( m_channelsLabel );
	ll->addWidget( m_freqLabel );
	ll->addWidget( m_bitsLabel );
 
	m_panSlider = new QSlider(Qt::Horizontal);
	m_panSlider->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
	m_panSlider->setMinimum( -100 );
	m_panSlider->setMaximum( +100 );
	m_panSlider->setValue( 0 );
 
	m_volSlider = new QSlider(Qt::Horizontal);
	m_volSlider->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
	m_volSlider->setMinimum( 0 );
	m_volSlider->setMaximum( +100 );
	m_volSlider->setValue( 100 );
 
	/* spinbox */
	m_freqControl = new QDoubleSpinBox();
	m_freqControl->setMinimum( 0.0 );
	m_freqControl->setMaximum( 3.0 );
	m_freqControl->setValue( 1.0 );
	m_freqControl->setSingleStep( 0.1 );
	m_freqControl->setWrapping(1);
 
	QVBoxLayout* vl = new QVBoxLayout();
	vl->addLayout(ll);
 
	vl->addWidget(m_panSlider);
	vl->addWidget(m_volSlider);
 
	vl->addWidget(m_freqControl);
	setLayout(vl);
 
	connect(m_panSlider,   SIGNAL( valueChanged(int) ),    this,          SLOT( panValueChanged(int) ) );
	connect(m_volSlider,   SIGNAL( valueChanged(int) ),    this,          SLOT( volValueChanged(int) ) );
	connect(m_freqControl, SIGNAL( valueChanged(double) ),this, SLOT( freqChanged( double ) ) );
}

PanelInfo::PanelInfo(QWidget* parent /* = 0 */ )
: QFrame(parent)
{
	setFrameStyle( QFrame::Box | QFrame::Raised );
  
        setMinimumSize( QSize(120, 240) );
	setSizePolicy( QSizePolicy::Fixed, QSizePolicy::Fixed );

	/* labels */
	m_durationLabel = new QLabel("DURATION");
	m_channelsLabel = new QLabel("CHANNELS");
	m_freqLabel = new QLabel("FREQ");
	m_bitsLabel = new QLabel("BITS");

	QVBoxLayout* ll = new QVBoxLayout();
	ll->setContentsMargins(0, 0, 0, 0);
        ll->setSpacing(0); //<---doesn't work in my case
	ll->addWidget( m_durationLabel );
	ll->addWidget( m_channelsLabel );
	ll->addWidget( m_freqLabel );
	ll->addWidget( m_bitsLabel );

	m_panSlider = new QSlider(Qt::Horizontal);
	m_panSlider->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
	m_panSlider->setMinimum( -100 );
	m_panSlider->setMaximum( +100 );
	m_panSlider->setValue( 0 );

	m_volSlider = new QSlider(Qt::Horizontal);
	m_volSlider->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
	m_volSlider->setMinimum( 0 );
	m_volSlider->setMaximum( +100 );
	m_volSlider->setValue( 100 );

	/* spinbox */
	m_freqControl = new QDoubleSpinBox();
	m_freqControl->setMinimum( 0.0 );
	m_freqControl->setMaximum( 3.0 );
	m_freqControl->setValue( 1.0 );
	m_freqControl->setSingleStep( 0.1 );
	m_freqControl->setWrapping(1);

	QVBoxLayout* vl = new QVBoxLayout();
	vl->addLayout(ll);

	vl->addWidget(m_panSlider);
	vl->addWidget(m_volSlider);

	vl->addWidget(m_freqControl);
	setLayout(vl);

	connect(m_panSlider,   SIGNAL( valueChanged(int) ),    this,          SLOT( panValueChanged(int) ) );
	connect(m_volSlider,   SIGNAL( valueChanged(int) ),    this,          SLOT( volValueChanged(int) ) );
	connect(m_freqControl, SIGNAL( valueChanged(double) ),this, SLOT( freqChanged( double ) ) );
}

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The result is that I have some not desired spaces between the labels also setting setSpacing to 0px. Layout are not completely clear to me.
In the attached image I drawn some red lines indicating the spaces I would delete.

Best