Distorted microphone audio when the loudspeaker is enabled (Xamarin.iOS) - audio

I am maintaining a Push-to-talk VoIP app.
When a PTT call is running the app create an audio session
m_AudioSession = AVAudioSession.SharedInstance();
NSError error;
if (!m_AudioSession.SetCategory(AVAudioSession.CategoryPlayAndRecord, AVAudioSessionCategoryOptions.DefaultToSpeaker | AVAudioSessionCategoryOptions.AllowBluetooth, out error))
{
IOSErrorLogger.Log(DammLoggerLevel.Error, TAG, error, "Error setting the category");
}
if (!m_AudioSession.SetMode(AVAudioSession.ModeVoiceChat, out error))
{
IOSErrorLogger.Log(DammLoggerLevel.Error, TAG, error, "Error setting the mode");
}
if (!m_AudioSession.OverrideOutputAudioPort(AVAudioSessionPortOverride.Speaker, out error))
{
IOSErrorLogger.Log(DammLoggerLevel.Error, TAG, error, "Error redirecting the audio to the loudspeaker");
}
if (!m_AudioSession.SetPreferredIOBufferDuration(0.06, out error)) // 60 milli seconds
{
IOSErrorLogger.Log(DammLoggerLevel.Error, TAG, error, "Error setting the preferred buffer duration");
}
if (!m_AudioSession.SetPreferredSampleRate(8000, out error)) // kHz
{
IOSErrorLogger.Log(DammLoggerLevel.Error, TAG, error, "Error setting the preferred sample rate");
}
if (!m_AudioSession.SetActive(true, out error))
{
IOSErrorLogger.Log(DammLoggerLevel.Error, TAG, error, "Error activating the audio session");
}
The received audio is played using the OutputAudioQueue and the microphone audio is captured (as mentioned in the Apple Doc: https://developer.apple.com/documentation/avfaudio/avaudiosession/mode/1616455-voicechat) using a Voice-Processing I/O Unit.
The initialization code for Voice-Processing I/O Unit is:
AudioStreamBasicDescription audioFormat = new AudioStreamBasicDescription()
{
SampleRate = SAMPLERATE_8000,
Format = AudioFormatType.LinearPCM,
FormatFlags = AudioFormatFlags.LinearPCMIsSignedInteger | AudioFormatFlags.LinearPCMIsPacked,
FramesPerPacket = 1,
ChannelsPerFrame = CHANNELS,
BitsPerChannel = BITS_X_SAMPLE,
BytesPerPacket = BYTES_X_SAMPLE,
BytesPerFrame = BYTES_X_FRAME,
Reserved = 0
};
AudioComponent audioComp = AudioComponent.FindComponent(AudioTypeOutput.VoiceProcessingIO);
AudioUnit.AudioUnit voiceProcessing = new AudioUnit.AudioUnit(audioComp);
AudioUnitStatus unitStatus = AudioUnitStatus.NoError;
unitStatus = voiceProcessing.SetEnableIO(true, AudioUnitScopeType.Input, ELEM_Mic);
if (unitStatus != AudioUnitStatus.NoError)
{
DammLogger.Log(DammLoggerLevel.Warn, TAG, "Audio Unit SetEnableIO(true, AudioUnitScopeType.Input, ELEM_Mic) returned: {0}", unitStatus);
}
unitStatus = voiceProcessing.SetEnableIO(true, AudioUnitScopeType.Output, ELEM_Speaker);
if (unitStatus != AudioUnitStatus.NoError)
{
DammLogger.Log(DammLoggerLevel.Warn, TAG, "Audio Unit SetEnableIO(false, AudioUnitScopeType.Output, ELEM_Speaker) returned: {0}", unitStatus);
}
unitStatus = voiceProcessing.SetFormat(audioFormat, AudioUnitScopeType.Output, ELEM_Mic);
if (unitStatus != AudioUnitStatus.NoError)
{
DammLogger.Log(DammLoggerLevel.Warn, TAG, "Audio Unit SetFormat (MIC-OUTPUT) returned: {0}", unitStatus);
}
unitStatus = voiceProcessing.SetFormat(audioFormat, AudioUnitScopeType.Input, ELEM_Speaker);
if (unitStatus != AudioUnitStatus.NoError)
{
DammLogger.Log(DammLoggerLevel.Warn, TAG, "Audio Unit SetFormat (ELEM 0-INPUT) returned: {0}", unitStatus);
}
unitStatus = voiceProcessing.SetRenderCallback(AudioUnit_RenderCallback, AudioUnitScopeType.Input, ELEM_Speaker);
if (unitStatus != AudioUnitStatus.NoError)
{
DammLogger.Log(DammLoggerLevel.Warn, TAG, "Audio Unit SetRenderCallback returned: {0}", unitStatus);
}
...
voiceProcessing.Initialize();
voiceProcessing.Start();
And the RenderCallback function is:
private AudioUnitStatus AudioUnit_RenderCallback(AudioUnitRenderActionFlags actionFlags, AudioTimeStamp timeStamp, uint busNumber, uint numberFrames, AudioBuffers data)
{
AudioUnit.AudioUnit voiceProcessing = m_VoiceProcessing;
if (voiceProcessing != null)
{
// getting microphone input signal
var status = voiceProcessing.Render(ref actionFlags, timeStamp, ELEM_Mic, numberFrames, data);
if (status != AudioUnitStatus.OK)
{
return status;
}
if (data.Count > 0)
{
unsafe
{
short* samples = (short*)data[0].Data.ToPointer();
for (uint idxSrcFrame = 0; idxSrcFrame < numberFrames; idxSrcFrame++)
{
... send the collected microphone audio (samples[idxSrcFrame])
}
}
}
}
return AudioUnitStatus.NoError;
}
I am facing the problem that if the loudspeaker is enabled: m_AudioSession.OverrideOutputAudioPort(AVAudioSessionPortOverride.Speaker, out error)
then the microphone audio is corrupted (some times is impossible to understand the speech).
If the loudspeaker is NOT enabled (the AVAudioSessionPortOverride.Speaker is not set) then the audio is very nice.
I have already verified that the NumberChannels in the AudioBuffer returned by the Render function is 1 (mono audio).
Any hit helping solved the problem is very appreciated. Thanks
Update:
The AudioUnit_RenderCallback method is called every 32 ms. When the loudspeaker is disabled the received number of frames is 256 which is exact (sample rate is 8000). When the loudspeaker is enabled the received number of frames is 85.
In both cases the GetAudioFormat returns the expected values: BitsPerChannel=16, BytesPerFrame=2, FramesPerPacket=1, ChannelsPerFrame=1, SampleRate=8000
Update:
I end up using the Sample Rate from the Hardware and performing the down-sampling self. It is must understanding that the Audio Unit should be able to perform the down sampling https://developer.apple.com/library/archive/documentation/MusicAudio/Conceptual/AudioUnitHostingGuide_iOS/AudioUnitHostingFundamentals/AudioUnitHostingFundamentals.html#//apple_ref/doc/uid/TP40009492-CH3-SW11)) but it was not possible for me to make it working when the loudspeaker was enabled.

I hope you are testing this on an actual device and not a simulator.
In the code, have you tried using this:
sampleRate = AudioSession.CurrentHardwareSampleRate;
Rather than forcing the sample rate, it's best to check the sample rate from the Hardware. It could be that during loudspeaker usage, it changes the sample rate and thus creating an issue.
I would suggest recording based on the above changes and see if the audio improves and then experiment with other flags.
Standard recording pattern:
https://learn.microsoft.com/en-us/dotnet/api/audiotoolbox.audiostreambasicdescription?view=xamarin-ios-sdk-12#remarks

Related

CAN socketCAN - how reliable is for file transfer

I want to send files (mp3 about 4MB each) to devices connected via CAN. I'm testing with Linux machine and ESP32. The problem is that not all data arrives to destination.
I'm sending from Linux machine using socketCAN and UCCB USB-CAN converter
https://www.tindie.com/products/lll7/can-usb-converter-uccb/ to ESP32, or between two ESP32.
When sending from PC Linux to ESP32, sometimes only 1/3 of mp3 file is saved, during sending I have candump slcan0 command running and it looks like all data is on the bus, but ESP32 does not see some frames.
When I send between two ESP32, for instance 4MB of data, receiving ESP32 gets around 3,98MB of data, some frames gets lost.
I'm using command "slcand -o -c -f -s8 /dev/ttyACM0 slcan0" to create slcan0 interface, although changing the speed with -s switch does not seem to work.
Am I missing something, or CAN is not suitable for such high speed, high load operations? I want to have 30 devices on canbus that receive around 1GB of data (mp3 files)
code below:
CanMgr::CanMgr(QObject *parent,LogModel *logModel):QObject(parent) {
this->logModel=logModel;
send_timer=new QTimer(this);
send_timer->setSingleShot(true);
send_timer->setInterval(1);
connect(send_timer,&QTimer::timeout,this,&CanMgr::processQueue);
}
void CanMgr::connectDevice() {
QString errorString;
m_canDevice = QCanBus::instance()->createDevice(m_pluginName,m_socketName,&errorString);
if (!m_canDevice) {
qDebug()<<QString("Error creating device '%1', reason: '%2'").arg(m_pluginName).arg(errorString);
return;
}
m_numberFramesWritten = 0;
connect(m_canDevice, &QCanBusDevice::errorOccurred, this, &CanMgr::processErrors);
connect(m_canDevice, &QCanBusDevice::framesReceived, this, &CanMgr::processReceivedFrames);
connect(m_canDevice, &QCanBusDevice::framesWritten, this, &CanMgr::processFramesWritten);
connect(m_canDevice, &QCanBusDevice::stateChanged,this, &CanMgr::stateChanged);
m_canDevice->setConfigurationParameter(QCanBusDevice::BitRateKey,"250000");
if (!m_canDevice->connectDevice()) {
qDebug()<<tr("Connection error: %1").arg(m_canDevice->errorString());
delete m_canDevice;
m_canDevice = nullptr;
} else {
QVariant bitRate = m_canDevice->configurationParameter(QCanBusDevice::BitRateKey);
if (bitRate.isValid()) {
qDebug()<<tr("Plugin: %1, connected to %2 at %3 kBit/s").arg(m_pluginName).arg(m_socketName).arg(bitRate.toInt() / 1000);
} else {
qDebug()<<tr("Plugin: %1, connected to %2").arg(m_pluginName).arg(m_socketName);
}
}
}
void CanMgr::sendFileContent(QByteArray data) {
quint32 frameId = 0;
quint32 dev_id=2;
quint32 cmd_id=0;
frameId=(dev_id<<16) | cmd_id;
m_canDevice->clear();
QByteArray size=Helper::byteArrFromInt((quint32)data.size(),8);
qDebug()<<"CanMgr::sendFileContent file size in bytes:"<<Helper::printHex(size);
QCanBusFrame frame = QCanBusFrame(frameId,size);
frame.setExtendedFrameFormat(true);
qDebug()<<"frame data:"<<frame.toString()<<" stat:"<<m_canDevice->state();
queue.append(frame);
frameId = 0;
dev_id=2;
cmd_id=1;
frameId=(dev_id<<16) | cmd_id;
for(int i=0;i<data.size();i+=8) {
QCanBusFrame frame = QCanBusFrame(frameId, data.mid(i,8));
frame.setExtendedFrameFormat(true);
queue.append(frame);
}
frameId = 0;
dev_id=2;
cmd_id=2;
frameId=(dev_id<<16) | cmd_id;
frame = QCanBusFrame(frameId, size);
frame.setExtendedFrameFormat(true);
queue.append(frame);
process_frame=false;
send_timer->start();
}
void CanMgr::processQueue() {
if(queue.isEmpty()) {
qDebug()<<"CanMgr::processQueu queue empty";
return;
}
if(process_frame) {
;
}
else {
curr_frame=queue.dequeue();
process_frame=true;
}
qDebug()<<"CanMgr::processQueue frame data:"<<curr_frame.toString()<<" towrite:"<<m_canDevice->framesToWrite()<<" left:"<<queue.count();
m_canDevice->writeFrame(curr_frame);
}
void CanMgr::processFramesWritten(qint64 count) {
qDebug()<<"CanMgr::processFramesWritten count:"<<count;
process_frame=false;
this->processQueue();
}
QString CanMgr::processErrors(QCanBusDevice::CanBusError error) const
{
QString err_str;
switch (error) {
case QCanBusDevice::ReadError:
case QCanBusDevice::WriteError:
case QCanBusDevice::ConnectionError:
case QCanBusDevice::ConfigurationError:
case QCanBusDevice::UnknownError:
err_str= m_canDevice->errorString();
qDebug()<<"Error:"<<err_str;
send_timer->start();
return err_str;
break;
default:
break;
}
}
Best,
Marek

How to play sound onto microphone?

I want to make a soundboard in the Processing language that plays sounds so the computer handles the sounds as if they were inputs from my microphone. This is my only problem about doing a soundboard. How do I make the sounds play as if they were recorded by the microphone?
I have spent an hour searching and trying to get help, but I have nothing to work with.
Minim provides the class AudioInput for monitoring the user’s current record source (this is often set in the sound card control panel), such as the microphone or the line-in
from
http://code.compartmental.net/tools/minim/quickstart/
EDIT:
Have you seen this?
import ddf.minim.*;
import ddf.minim.ugens.*;
Minim minim;
// for recording
AudioInput in;
AudioRecorder recorder;
// for playing back
AudioOutput out;
FilePlayer player;
void setup()
{
size(512, 200, P3D);
minim = new Minim(this);
// get a stereo line-in: sample buffer length of 2048
// default sample rate is 44100, default bit depth is 16
in = minim.getLineIn(Minim.STEREO, 2048);
// create an AudioRecorder that will record from in to the filename specified.
// the file will be located in the sketch's main folder.
recorder = minim.createRecorder(in, "myrecording.wav");
// get an output we can playback the recording on
out = minim.getLineOut( Minim.STEREO );
textFont(createFont("Arial", 12));
}
void draw()
{
background(0);
stroke(255);
// draw the waveforms
// the values returned by left.get() and right.get() will be between -1 and 1,
// so we need to scale them up to see the waveform
for(int i = 0; i < in.left.size()-1; i++)
{
line(i, 50 + in.left.get(i)*50, i+1, 50 + in.left.get(i+1)*50);
line(i, 150 + in.right.get(i)*50, i+1, 150 + in.right.get(i+1)*50);
}
if ( recorder.isRecording() )
{
text("Now recording...", 5, 15);
}
else
{
text("Not recording.", 5, 15);
}
}
void keyReleased()
{
if ( key == 'r' )
{
// to indicate that you want to start or stop capturing audio data,
// you must callstartRecording() and stopRecording() on the AudioRecorder object.
// You can start and stop as many times as you like, the audio data will
// be appended to the end of to the end of the file.
if ( recorder.isRecording() )
{
recorder.endRecord();
}
else
{
recorder.beginRecord();
}
}
if ( key == 's' )
{
// we've filled the file out buffer,
// now write it to a file of the type we specified in setup
// in the case of buffered recording,
// this will appear to freeze the sketch for sometime, if the buffer is large
// in the case of streamed recording,
// it will not freeze as the data is already in the file and all that is being done
// is closing the file.
// save returns the recorded audio in an AudioRecordingStream,
// which we can then play with a FilePlayer
if ( player != null )
{
player.unpatch( out );
player.close();
}
player = new FilePlayer( recorder.save() );
player.patch( out );
player.play();
}
}
It's from here:
http://code.compartmental.net/minim/audiorecorder_class_audiorecorder.html

visual c++ Serialport class handling data very slow

I'm trying to handle data recieved at about 1Hz from a robot through a serialport (bluetooth connection). I will recieve data with different headers determining what data will be recieved and what the expected length of the message is.
for example:
Header: sensorvalues (0x32) -> expected length 11 incl. header.
First i want to check if the byte is a header and if thats the case extract the expected length (in bytes).
I am using vc++ and the serialport class in the GUI.
The "seirialport->read(buffer, 0, expected length)" is very slow and not very reliable. I found some tips at http://www.sparxeng.com/blog/software/must-use-net-system-io-ports-serialport but the buffer still builds up to the point where I have about 200 bytes in the buffer, which is not very good when i need live sensorvalues displayed on the GUI.
The key parts of my code are:
System::Void MyForm::serialPort1_DataReceived_1(System::Object^ sender, System::IO::Ports::SerialDataReceivedEventArgs^ e) {
if (serialPort1->BytesToRead > 0){
if (write_position == 0){
serialPort1->BaseStream->ReadAsync(data_recieved_buffer, 0, 1);
header = data_recieved_buffer[0];
if (this->InvokeRequired){
myrecievedata_delegate^ d = gcnew myrecievedata_delegate(&myrecievedata);
this->Invoke(d, gcnew array < Object^ > {'h'});
}
else
{
myrecievedata('h');
}
}
else if (this->serialPort1->BytesToRead > expected_length - 1)
{
serialPort1->BaseStream->ReadAsync(data_recieved_buffer, 0, expected_length - 1);
if (this->InvokeRequired){
myrecievedata_delegate^ d = gcnew myrecievedata_delegate(&myrecievedata);
this->Invoke(d, gcnew array < Object^ > {'b'});
}
else
{
myrecievedata('b');
}
}
else{
return;
}
}
and the recieved data is sent to
System::Void MyForm::myrecievedata(char status){
if (status == 'h'){
handleheader(header);
}
else if (status == 'b'){
handlebyte();
}
Is the problem at the serialport_datarecieved event? I can only think of invoke (which I have very little knowledge about) being the problem, still keeping the work in the serialport thread.
If that is the case how would I make sure that the data is handled in a different thread?
Thanks in advance!

Android OpenSL ES - issue with .wav file sampled at 44.1Khz

I'm trying to convert some of my OpenAL code to OpenSL ES for my Android usage (Kitkat 4.4.4) on Genymotion and encountered an issue with .wav files sampled at 44.1Khz. My application is a native one (glue).
I've followed the /native-audio sample of Android NDK samples and fragments from the excellent book Android NDK Beginners Guide, so my code behaves correctly on most of wav/PCM data, except those sampled at 44.1Khz. My specific code is this:
Engine init
// create OpenSL ES engine
SLEngineOption EngineOption[] = {(SLuint32) SL_ENGINEOPTION_THREADSAFE, (SLuint32) SL_BOOLEAN_TRUE};
const SLInterfaceID lEngineMixIIDs[] = {SL_IID_ENGINE};
const SLboolean lEngineMixReqs[] = {SL_BOOLEAN_TRUE};
SLresult res = slCreateEngine(&mEngineObj, 1, EngineOption, 1, lEngineMixIIDs, lEngineMixReqs);
res = (*mEngineObj)->Realize(mEngineObj, SL_BOOLEAN_FALSE);
res = (*mEngineObj)->GetInterface(mEngineObj, SL_IID_ENGINE, &mEngine); // get 'engine' interface
// create output mix (AKA playback; this represents speakers, headset etc.)
res = (*mEngine)->CreateOutputMix(mEngine, &mOutputMixObj, 0,NULL, NULL);
res = (*mOutputMixObj)->Realize(mOutputMixObj, SL_BOOLEAN_FALSE);
Player init
SLresult lRes;
// Set-up sound audio source.
SLDataLocator_AndroidSimpleBufferQueue lDataLocatorIn;
lDataLocatorIn.locatorType = SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE;
lDataLocatorIn.numBuffers = 1; // 1 buffer for a one-time load
// analyze and set correct PCM format
SLDataFormat_PCM lDataFormat;
lDataFormat.formatType = SL_DATAFORMAT_PCM;
lDataFormat.numChannels = audio->wav.channels; // etc. 1,2
lDataFormat.samplesPerSec = audio->wav.sampleRate * 1000; // etc. 44100 * 1000
lDataFormat.bitsPerSample = audio->wav.bitsPerSample; // etc. 16
lDataFormat.containerSize = audio->wav.bitsPerSample;
lDataFormat.channelMask = SL_SPEAKER_FRONT_CENTER;
lDataFormat.endianness = SL_BYTEORDER_LITTLEENDIAN;
SLDataSource lDataSource;
lDataSource.pLocator = &lDataLocatorIn;
lDataSource.pFormat = &lDataFormat;
SLDataLocator_OutputMix lDataLocatorOut;
lDataLocatorOut.locatorType = SL_DATALOCATOR_OUTPUTMIX;
lDataLocatorOut.outputMix = mOutputMixObj;
SLDataSink lDataSink;
lDataSink.pLocator = &lDataLocatorOut;
lDataSink.pFormat = NULL;
const SLInterfaceID lSoundPlayerIIDs[] = { SL_IID_PLAY, SL_IID_ANDROIDSIMPLEBUFFERQUEUE };
const SLboolean lSoundPlayerReqs[] = { SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE };
lRes = (*mEngine)->CreateAudioPlayer(mEngine, &mPlayerObj, &lDataSource, &lDataSink, 2, lSoundPlayerIIDs, lSoundPlayerReqs);
if (lRes != SL_RESULT_SUCCESS) { return; }
lRes = (*mPlayerObj)->Realize(mPlayerObj, SL_BOOLEAN_FALSE);
if (lRes != SL_RESULT_SUCCESS) { return; }
lRes = (*mPlayerObj)->GetInterface(mPlayerObj, SL_IID_PLAY, &mPlayer);
if (lRes != SL_RESULT_SUCCESS) { return; }
lRes = (*mPlayerObj)->GetInterface(mPlayerObj, SL_IID_ANDROIDSIMPLEBUFFERQUEUE, &mPlayerQueue);
if (lRes != SL_RESULT_SUCCESS) { return; }
// register callback on the buffer queue
lRes = (*mPlayerQueue)->RegisterCallback(mPlayerQueue, bqPlayerQueueCallback, NULL);
if (lRes != SL_RESULT_SUCCESS) { return; }
lRes = (*mPlayer)->SetCallbackEventsMask(mPlayer, SL_PLAYEVENT_HEADATEND);
if (lRes != SL_RESULT_SUCCESS) { return; }
// ..fetch the data in 'audio->data' from opened FILE* stream and set 'datasize'
// feed the buffer with data
lRes = (*mPlayerQueue)->Clear(mPlayerQueue); // remove any sound from buffer
lRes = (*mPlayerQueue)->Enqueue(mPlayerQueue, audio->data, datasize);
The above works good for 8000, 22050 and 32000 samples/sec but on 41100 samples, 4 out of 5 times it will repeat itself lots of time on first play. It's like having a door knocking sound effect that actually loops many times (about 50 times) by a single ->SetPlayState(..SL_PLAYSTATE_PLAYING); and in speed. Any obvious error on my code? a multi-threaded issue with these sampling? Anyone else have this kind of problem? Should i downsample on 41.1Khz cases ? Could it be a Genymotion problem? tx
I solved this by downsampling from 44Khz to 22Khz. Interestingly, this only happens on sounds containing 1 channel and 44,100 samples; in all other cases there's no problem.

How to monitor playback on ALSA via asoundlib?

I'm building an application that allows for ALSA configuration and in the GUI there is a peek meter that allows the client to see playback levels in realtime. I'm having a hard time determining what device to connect to because I don't know if ALSA has a default "loopback" or not and what it's called. I am also having trouble converting the read data into a sample, then finding said sample's amplitude. Here is what I have built so far:
Grab device and set hardware params
if (0 == snd_pcm_open(&pPcm, "default", SND_PCM_STREAM_CAPTURE, SND_PCM_NONBLOCK))
{
if (0 == snd_pcm_set_params(pPcm, SND_PCM_FORMAT_S16_LE, SND_PCM_ACCESS_RW_INTERLEAVED, 1, 96000, 1, 1)) // This last argument confuses me because I'm not given a unit of measurement (second, millisecond, mircosecond, etc.)
{
return snd_pcm_start(pPcm);
}
}
pPcm = nullptr;
return -1;
Read from device and return the peek of the audio signal
int iRtn = -1;
if (nullptr == pPcm)
{
if (-1 == SetupListener())
{
return iRtn;
}
}
// Check to make the state is sane for reading.
if (SND_PCM_STATE_PREPARED == snd_pcm_state(pPcm) ||
SND_PCM_STATE_RUNNING == snd_pcm_state(pPcm))
{
snd_pcm_resume(pPcm); // This might be superfluous.
// The state is sane, read from the stream.
signed short iBuffer = 0;
int iNumRead = snd_pcm_readi(pPcm, &iBuffer, 1);
if (0 < iNumRead)
{
// This calculates an approximation.
// We have some audio data, acquire it's peek in dB. (decibels)
float nSample = static_cast<float>(iBuffer);
float nAmplitude = nSample / MAX_AMPLITUDE_S16; // MAX_AMPLITUDE_S16 is defined as "32767"
float nDecibels = (0 < nAmplitude) ? 20 * log10(nAmplitude) : 0;
iRtn = static_cast<int>(nDecibels); // Cast to integer for GUI element.
}
}
return iRtn;
The ALSA documentation seems very barren and so I apologize if I'm misusing the API.

Resources