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

AUDIO_CURVE_TYPE_NONE Specifies that no curve algorithm will be applied. When this curve is specified, the duration of the curve specified must be equal to 0.
AUDIO_CURVE_TYPE_WINDOWS_FADE Specifies that the algorithm that is applied to the volume setting must follow the curve shown in the diagram in the Remarks section.

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

Requirement	Value
Minimum supported client	Windows 8
Header	ksmedia.h

See also

KSAUDIOENGINE_VOLUMELEVEL

KSPROPERTY_AUDIOENGINE_VOLUMELEVEL