playing created Audio-Data has noise and periodical clicking in sound - c++

Question

I write an application, which plays a sound getting from Hardware (like a ring buffer filled with a sinus wave with certain frequency). Everything works fine, and I can playback the created sound correctly except a periodical clicking (maybe at the end of buffer?) and noise.
I initialize and run the Buffer:
void Audiooutput::InitializeAudioParameters()
{
Audio_DataWritten = 0;
Audio_fragments = 4;
Audio_channels = 2;
Audio_BufferSize = 256;
Audio_Samplerate = 8000;
Audio_ResamplingFactor = 1;
Audio_Framesize = 2;
// (SND_PCM_FORMAT_S16_LE / 8);
Audio_frames = Audio_BufferSize / Audio_Framesize * Audio_fragments;
snd_pcm_uframes_t size;
err = snd_pcm_hw_params_any(pcmPlaybackHandle, hw_params);
err = snd_pcm_hw_params_set_rate_resample(pcmPlaybackHandle, hw_params, 1);
// qDebug()<<a1.sprintf(" % d \t snd_pcm_hw_params_set_rate: %s",Audio_Samplerate,snd_strerror(err));
err =
snd_pcm_hw_params_set_format(pcmPlaybackHandle, hw_params,
SND_PCM_FORMAT_S16_LE);
err =
snd_pcm_hw_params_set_channels(pcmPlaybackHandle, hw_params,
Audio_channels);
err = snd_pcm_hw_params_set_rate_near(pcmPlaybackHandle, hw_params, &Audio_Samplerate, 0);
// qDebug()<<a1.sprintf(" % d \t snd_pcm_hw_params_set_rate: %s",Audio_Samplerate,snd_strerror(err));
if ((err =
snd_pcm_hw_params_set_periods_near(pcmPlaybackHandle, hw_params,
&Audio_fragments, 0)) < 0) {
qDebug() << a1.sprintf("Error setting # fragments to %d: %s\n",
Audio_fragments, snd_strerror(err));
} else
qDebug() << a1.sprintf("setting # fragments to %d: %s\n",
Audio_fragments, snd_strerror(err));
err = snd_pcm_hw_params_get_buffer_size(hw_params, &size);
if ((err =
snd_pcm_hw_params_set_buffer_size_near(pcmPlaybackHandle,
hw_params,
&Audio_frames)) < 0) {
qDebug() << a1.
sprintf("Error setting buffer_size %d frames: %s",
Audio_frames, snd_strerror(err));
} else
qDebug() << a1.sprintf("setting Buffersize to %d --> %d: %s\n",
Audio_BufferSize, Audio_frames,
snd_strerror(err));
Audio_BufferSize = Audio_frames;
if ((err = snd_pcm_hw_params(pcmPlaybackHandle, hw_params)) < 0) {
qDebug() << a1.sprintf("Error setting HW params: %s",
snd_strerror(err));
}
Q_ASSERT(err >= 0);
}
void Audiooutput::ProduceAudioOutput(int n, int mmodes, int totalMModeGates,
short *sinusValue, short *cosinusValue)
{
for (int audioSample = 0; audioSample < n;
audioSample += Audio_ResamplingFactor) {
currentposition =
(int)(m_Audio.generalPos % (Audio_BufferSize / 2));
if (currentposition == 0) {
QueueAudioBuffer();
m_Audio.currentPos = 0;
}
m_Audio.generalPos++;
AudioData[currentposition * 2] =
(short)(sinusValue[audioSample]);
AudioData[currentposition * 2 + 1] =
(short)(cosinusValue[audioSample]);
}
}
void Audiooutput::QueueAudioBuffer()
{
snd_pcm_prepare(pcmPlaybackHandle);
Audio_DataWritten +=
snd_pcm_writei(pcmPlaybackHandle, AudioData, Audio_BufferSize);
}
Changing the audiobuffer size or fragments changes also the clicking period.
Can anyone help me with this issue ?
I checked also the first and Last Values. Thy are always difference.
OS: Ubuntu 11
more detail.
the count of received data is dynamically, and changes depend of different parameters. But I play always a certain part e.g. 128 values or 256 or 512....
// I get the Audiodata from a hardware (in a Timerloop)
audiobuffersize = 256;
short *AudioData = new short[256];
int generalAudioSample = 0;
void CollectDataFromHw()
{
...
int n = 0;
n = GetData(buf1,buf2);//buf1 = new short[MAX_SHRT]
if(n > 0)
FillAudioBuffer(n,buf1,buf2)
...
}
-------------------------------------------
void FillAudioBuffer(int n, short*buf1, short*buf2)
{
for(int audioSample = 0;audioSample < n; audioSample++){
iCurrentAudioSample = (int)(generalAudioSample % (audiobuffersize/2));
if(iCurrentAudioSample == 0) {
snd_pcm_writei(pcmPlaybackHandle,AudioData,audiobuffersize );
memset(AudioData,0x00,audiobuffersize*sizeof(short));
}
generalAudioSample++;
AudioData[iCurrentAudioSample * 2] = (short)(buf1[audioSample];
AudioData[iCurrentAudioSample * 2 +1] = (short)(buf2[audioSample];
}
}
I changed the audiobuffersize also. If I set it to a bigger size, I have some Echo additional to clicks.
any Idea ?
//-----------------------
the Problem is
snd_pcm_prepare(pcmPlaybackHandle);
every call of this function produce a click in sound !

Answer 1

Can't test the source code, but I think that the high-frequency clicks you hear are discontinuities in the sound wave. You have to assure that looping period (or, buffer size) is multiple of wave period.
Check if first and last value of buffer are almost the same (+/- 1, for example). Their distance determines the amplitude of the unwanted click.

Answer 2

solved
buffer has been played several times before it was filled with the data.
stupid error in the code.missing a parantez --> audio_buffersize/2 <--
and therefore the result was very often if(iCurrentAudioSample == 0) true !!!!!
iCurrentAudioSample = (int)(generalAudioSample % (audio_buffersize/2));
if(iCurrentAudioSample == 0)
{
writetoaudioStream(audiobuffer);
}