Pops / clicks when stopping and starting DirectX sound synth in C++ / MFC - c++

Question

I have made a soft synthesizer in Visual Studio 2012 with C++, MFC and DirectX. Despite having added code to rapidly fade out the sound I am experiencing popping / clicking when stopping playback (also when starting).
I copied the DirectX code from this project: http://www.codeproject.com/Articles/7474/Sound-Generator-How-to-create-alien-sounds-using-m
I'm not sure if I'm allowed to cut and paste all the code from the Code Project. Basically I use the Player class from that project as is, the instance of this class is called m_player in my code. The Stop member function in that class calls the Stop function of LPDIRECTSOUNDBUFFER:
void Player::Stop()
{
DWORD status;
if (m_lpDSBuffer == NULL)
return;
HRESULT hres = m_lpDSBuffer->GetStatus(&status);
if (FAILED(hres))
EXCEP(DirectSoundErr::GetErrDesc(hres), "Player::Stop GetStatus");
if ((status & DSBSTATUS_PLAYING) == DSBSTATUS_PLAYING)
{
hres = m_lpDSBuffer->Stop();
if (FAILED(hres))
EXCEP(DirectSoundErr::GetErrDesc(hres), "Player::Stop Stop");
}
}
Here is the notification code (with some supporting code) in my project that fills the sound buffer. Note that the rend function always returns a double between -1 to 1, m_ev_smps = 441, m_n_evs = 3 and m_ev_sz = 882. subInit is called from OnInitDialog:
#define FD_STEP 0.0005
#define SC_NOT_PLYD 0
#define SC_PLYNG 1
#define SC_FD_OUT 2
#define SC_FD_IN 3
#define SC_STPNG 4
#define SC_STPD 5
bool CMainDlg::subInit()
// initialises various variables and the sound player
{
Player *pPlayer;
SOUNDFORMAT format;
std::vector<DWORD> events;
int t, buf_sz;
try
{
pPlayer = new Player();
pPlayer->SetHWnd(m_hWnd);
m_player = pPlayer;
m_player->Init();
format.NbBitsPerSample = 16;
format.NbChannels = 1;
format.SamplingRate = 44100;
m_ev_smps = 441;
m_n_evs = 3;
m_smps = new short[m_ev_smps];
m_smp_scale = (int)pow(2, format.NbBitsPerSample - 1);
m_max_tm = (int)((double)m_ev_smps / (double)(format.SamplingRate * 1000));
m_ev_sz = m_ev_smps * format.NbBitsPerSample/8;
buf_sz = m_ev_sz * m_n_evs;
m_player->CreateSoundBuffer(format, buf_sz, 0);
m_player->SetSoundEventListener(this);
for(t = 0; t < m_n_evs; t++)
events.push_back((int)((t + 1)*m_ev_sz - m_ev_sz * 0.95));
m_player->CreateEventReadNotification(events);
m_status = SC_NOT_PLYD;
}
catch(MATExceptions &e)
{
MessageBox(e.getAllExceptionStr().c_str(), "Error initializing the sound player");
EndDialog(IDCANCEL);
return FALSE;
}
return TRUE;
}
void CMainDlg::Stop()
// stop playing
{
m_player->Stop();
m_status = SC_STPD;
}
void CMainDlg::OnBnClickedStop()
// causes fade out
{
m_status = SC_FD_OUT;
}
void CMainDlg::OnSoundPlayerNotify(int ev_num)
// render some sound samples and check for errors
{
ScopeGuardMutex guard(&m_mutex);
int s, end, begin, elapsed;
if (m_status != SC_STPNG)
{
begin = GetTickCount();
try
{
for(s = 0; s < m_ev_smps; s++)
{
m_smps[s] = (int)(m_synth->rend() * 32768 * m_fade);
if (m_status == SC_FD_IN)
{
m_fade += FD_STEP;
if (m_fade > 1)
{
m_fade = 1;
m_status = SC_PLYNG;
}
}
else if (m_status == SC_FD_OUT)
{
m_fade -= FD_STEP;
if (m_fade < 0)
{
m_fade = 0;
m_status = SC_STPNG;
}
}
}
}
catch(MATExceptions &e)
{
OutputDebugString(e.getAllExceptionStr().c_str());
}
try
{
m_player->Write(((ev_num + 1) % m_n_evs)*m_ev_sz, (unsigned char*)m_smps, m_ev_sz);
}
catch(MATExceptions &e)
{
OutputDebugString(e.getAllExceptionStr().c_str());
}
end = GetTickCount();
elapsed = end - begin;
if(elapsed > m_max_tm)
m_warn_msg.Format(_T("Warning! compute time: %dms"), elapsed);
else
m_warn_msg.Format(_T("compute time: %dms"), elapsed);
}
if (m_status == SC_STPNG)
Stop();
}
It seems like the buffer is not always sounding out when the stop button is clicked. I don't have any specific code for waiting for the sound buffer to finish playing before the DirectX Stop is called. Other than that the sound playback is working just fine, so at least I am initialising the player correctly and notification code is working in that respect.

Answer 1

Try replacing 32768 with 32767. Not by any means sure this is your issue, but it could overflow the positive short int range (assuming your audio is 16-bit) and cause a "pop".

Answer 2

I got rid of the pops / clicks when stopping playback, by filling the buffer with zeros after the fade out. However I still get pops when re-starting playback, despite filling with zeros and then fading back in (it is frustrating).