Source code
Revision control
Copy as Markdown
// Copyright (C) 2024 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#include "qtaudio.h"
#include <QtCore/qdebug.h>
#include <QtCore/qmath.h>
QT_BEGIN_NAMESPACE
#define LOG100 4.60517018599
/*!
\namespace QtAudio
\ingroup multimedia-namespaces
\brief The QtAudio namespace contains enums used by the audio classes.
\inmodule QtMultimedia
\ingroup multimedia
\ingroup multimedia_audio
*/
/*!
\enum QtAudio::Error
\value NoError No errors have occurred
\value OpenError An error occurred opening the audio device
\value IOError An error occurred during read/write of audio device. This can happen when
e.g. an external audio interface is disconnected.
\value UnderrunError \e{This value has been deprecated in Qt-6.11 and is not emitted from Qt. Observe
QtAudio::State::IdleState instead.}.
Audio data is not being fed to the audio device at a fast enough rate.
\value FatalError A non-recoverable error has occurred, the audio device is not usable at this time.
*/
/*!
\enum QtAudio::State
\value ActiveState Audio data is being processed, this state is set after start() is called
and while audio data is available to be processed.
\value SuspendedState The audio stream is in a suspended state. Entered after suspend() is called
or when another stream takes control of the audio device. In the later case,
a call to resume will return control of the audio device to this stream. This
should usually only be done upon user request.
\value StoppedState The audio device is closed, and is not processing any audio data
\value IdleState This state indicates that the audio system is temporarily idle due to
a buffering condition.
For a QAudioSink, IdleState means there isn’t enough data available
from the QIODevice to read.
For a QAudioSource, IdleState is entered when the ring buffer that
feeds the QIODevice becomes full. In that case, any new audio data
arriving from the audio interface is discarded until the application
reads from the QIODevice, which frees up space in the buffer.
*/
/*!
\enum QtAudio::VolumeScale
This enum defines the different audio volume scales.
\value LinearVolumeScale Linear scale. \c 0.0 (0%) is silence and \c 1.0 (100%) is full
volume. All Qt Multimedia classes that have an audio volume use
a linear scale.
\value CubicVolumeScale Cubic scale. \c 0.0 (0%) is silence and \c 1.0 (100%) is full
volume.
\value LogarithmicVolumeScale Logarithmic Scale. \c 0.0 (0%) is silence and \c 1.0 (100%) is
full volume. UI volume controls should usually use a logarithmic
scale.
\value DecibelVolumeScale Decibel (dB, amplitude) logarithmic scale. \c -200 is silence
and \c 0 is full volume.
\sa QtAudio::convertVolume()
*/
namespace QtAudio
{
/*!
Converts an audio \a volume \a from a volume scale \a to another, and returns the result.
Depending on the context, different scales are used to represent audio volume. All Qt Multimedia
classes that have an audio volume use a linear scale, the reason is that the loudness of a
speaker is controlled by modulating its voltage on a linear scale. The human ear on the other
hand, perceives loudness in a logarithmic way. Using a logarithmic scale for volume controls
is therefore appropriate in most applications. The decibel scale is logarithmic by nature and
is commonly used to define sound levels, it is usually used for UI volume controls in
professional audio applications. The cubic scale is a computationally cheap approximation of a
logarithmic scale, it provides more control over lower volume levels.
The following example shows how to convert the volume value from a slider control before passing
it to a QMediaPlayer. As a result, the perceived increase in volume is the same when increasing
the volume slider from 20 to 30 as it is from 50 to 60:
\snippet multimedia-snippets/audio.cpp Volume conversion
\sa VolumeScale, QAudioSink::setVolume(), QAudioSource::setVolume(),
QSoundEffect::setVolume()
*/
float convertVolume(float volume, VolumeScale from, VolumeScale to)
{
switch (from) {
case LinearVolumeScale:
volume = qMax(float(0), volume);
switch (to) {
case LinearVolumeScale:
return volume;
case CubicVolumeScale:
return qPow(volume, float(1 / 3.0));
case LogarithmicVolumeScale:
return 1 - std::exp(-volume * LOG100);
case DecibelVolumeScale:
if (volume < 0.001)
return float(-200);
else
return float(20.0) * std::log10(volume);
}
break;
case CubicVolumeScale:
volume = qMax(float(0), volume);
switch (to) {
case LinearVolumeScale:
return volume * volume * volume;
case CubicVolumeScale:
return volume;
case LogarithmicVolumeScale:
return 1 - std::exp(-volume * volume * volume * LOG100);
case DecibelVolumeScale:
if (volume < 0.001)
return float(-200);
else
return float(3.0 * 20.0) * std::log10(volume);
}
break;
case LogarithmicVolumeScale:
volume = qMax(float(0), volume);
switch (to) {
case LinearVolumeScale:
if (volume > 0.99)
return 1;
else
return -std::log(1 - volume) / LOG100;
case CubicVolumeScale:
if (volume > 0.99)
return 1;
else
return qPow(-std::log(1 - volume) / LOG100, float(1 / 3.0));
case LogarithmicVolumeScale:
return volume;
case DecibelVolumeScale:
if (volume < 0.001)
return float(-200);
else if (volume > 0.99)
return 0;
else
return float(20.0) * std::log10(-std::log(1 - volume) / LOG100);
}
break;
case DecibelVolumeScale:
switch (to) {
case LinearVolumeScale:
return qPow(float(10.0), volume / float(20.0));
case CubicVolumeScale:
return qPow(float(10.0), volume / float(3.0 * 20.0));
case LogarithmicVolumeScale:
if (qFuzzyIsNull(volume))
return 1;
else
return 1 - std::exp(-qPow(float(10.0), volume / float(20.0)) * LOG100);
case DecibelVolumeScale:
return volume;
}
break;
}
return volume;
}
} // namespace QtAudio
#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, QAudio::Error error)
{
QDebugStateSaver saver(dbg);
dbg.nospace();
switch (error) {
case QAudio::NoError:
dbg << "NoError";
break;
case QAudio::OpenError:
dbg << "OpenError";
break;
case QAudio::IOError:
dbg << "IOError";
break;
QT_WARNING_PUSH;
QT_WARNING_DISABLE_DEPRECATED;
case QAudio::UnderrunError:
dbg << "UnderrunError";
break;
QT_WARNING_POP;
case QAudio::FatalError:
dbg << "FatalError";
break;
}
return dbg;
}
QDebug operator<<(QDebug dbg, QAudio::State state)
{
QDebugStateSaver saver(dbg);
dbg.nospace();
switch (state) {
case QAudio::ActiveState:
dbg << "ActiveState";
break;
case QAudio::SuspendedState:
dbg << "SuspendedState";
break;
case QAudio::StoppedState:
dbg << "StoppedState";
break;
case QAudio::IdleState:
dbg << "IdleState";
break;
}
return dbg;
}
QDebug operator<<(QDebug dbg, QAudio::VolumeScale scale)
{
QDebugStateSaver saver(dbg);
dbg.nospace();
switch (scale) {
case QAudio::LinearVolumeScale:
dbg << "LinearVolumeScale";
break;
case QAudio::CubicVolumeScale:
dbg << "CubicVolumeScale";
break;
case QAudio::LogarithmicVolumeScale:
dbg << "LogarithmicVolumeScale";
break;
case QAudio::DecibelVolumeScale:
dbg << "DecibelVolumeScale";
break;
}
return dbg;
}
#endif
QT_END_NAMESPACE