Setting Effects on Buffers

You can set any number of effects on a secondary buffer that was created with the DSBCAPS_CTRLFX flag in the DSBUFFERDESC structure. The buffer must be stopped and not locked. In DirectX 9.0, effects are never hardware-accelerated. It is possible to set an effect on a hardware buffer, but doing so confers no advantages.

Effects might not work smoothly on very small buffers. DirectSound does not permit the creation of effects-capable buffers that hold less than 150 milliseconds of data. This value is defined as DSBSIZE_FX_MIN.

The following sample function sets an echo effect on a buffer and displays the result in the output window of the development environment.

HRESULT SetEcho(LPDIRECTSOUNDBUFFER8 pDSBuffer)
{
  HRESULT hr;
  DWORD dwResults[1];  // One element for each effect.
 
  // Describe the effect.
  DSEFFECTDESC dsEffect;
  memset(&dsEffect, 0, sizeof(DSEFFECTDESC));
  dsEffect.dwSize = sizeof(DSEFFECTDESC);
  dsEffect.dwFlags = 0;
  dsEffect.guidDSFXClass = GUID_DSFX_STANDARD_ECHO;
 
  // Set the effect
  if (SUCCEEDED(hr = pDSBuffer->SetFX(1, &dsEffect, dwResults)))
  {
    switch (dwResults[0])
    {
      case DSFXR_LOCHARDWARE:
        OutputDebugString("Effect was placed in hardware.");
        break;
      case DSFXR_LOCSOFTWARE:
        OutputDebugString("Effect was placed in software.");
        break;
      case DSFXR_UNALLOCATED:
        OutputDebugString("Effect is not yet allocated to hardware or software.");
        break;
    }
  }
  return hr;
}