AUDIO_CURVE_TYPE enumeration (ksmedia.h)

The AUDIO_CURVE_TYPE enumeration defines constants that specify a curve algorithm to be applied to set a volume level.

Syntax

typedef enum {
  AUDIO_CURVE_TYPE_NONE,
  AUDIO_CURVE_TYPE_WINDOWS_FADE
} AUDIO_CURVE_TYPE;

Constants

Remarks

The following snippet of pseudocode shows the logic for the algorithm that is applied to the volume setting to reach the target volume level.

// POWER IN AMPLITUDE: 1.75

// Fade In:
// Curve begins at 0 when nFrame = 0
// When nFrame gets to (nFrames - 1), curve = 1
//
// curve = pow(nFrame / (nFrames - 1), exponent)

float fFrameCount = nFrames - 1.0f;
for (UINT32 nFrame = 0; nFrame < nFrames; nFrame++) {
    float curve = powf(nFrame / fFrameCount, 1.75f);
    for (UINT32 nChannel = 0; nChannel < pWfx->nChannels; nChannel++) {
            pFloat[nFrame * pWfx->nChannels + nChannel] *= curve;
    }
}

// Fade Out:
// curve begins at 1 when nFrame = 0
// When nFrame gets to (nFrames - 1), curve = 0
//
// curve = pow(1 - (nFrame / (nFrames - 1)), exponent)

float fFrameCount = nFrames - 1.0f;
for (UINT32 nFrame = 0; nFrame < nFrames; nFrame++) {
    float curve = powf(1.0f - (nFrame / fFrameCount), 1.75f);
    for (UINT32 nChannel = 0; nChannel < pWfx->nChannels; nChannel++) {
            pFloat[nFrame * pWfx->nChannels + nChannel] *= curve;
    }
}

And the following diagram shows a graphical representation of the preceding pseudocode for setting the volume level.

Requirements

See also

KSAUDIOENGINE_VOLUMELEVEL

KSPROPERTY_AUDIOENGINE_VOLUMELEVEL