/// <summary>
/// Transposes down the sample rate, causing the observed playback
/// 'rate' of the sound to increase
/// </summary>
private void Downsample(ArrayPtr <TSampleType> src, int numSamples)
{
// If the parameter 'uRate' value is larger than 'SCALE', first apply the
// anti-alias filter to remove high frequencies (prevent them from folding
// over the lover frequencies), then transpose.
// Add the new samples to the end of the storeBuffer
_storeBuffer.PutSamples(src, numSamples);
// Anti-alias filter the samples to prevent folding and output the filtered
// data to tempBuffer. Note : because of the FIR filter length, the
// filtering routine takes in 'filter_length' more samples than it outputs.
Debug.Assert(_tempBuffer.IsEmpty);
var sizeTemp = _storeBuffer.AvailableSamples;
int count = _antiAliasFilter.Evaluate(_tempBuffer.PtrEnd(sizeTemp), _storeBuffer.PtrBegin(), sizeTemp, _channels);
if (count == 0)
{
return;
}
// Remove the filtered samples from 'storeBuffer'
_storeBuffer.ReceiveSamples(count);
// Transpose the samples (+16 is to reserve some slack in the destination buffer)
sizeTemp = (int)(numSamples / Rate + 16.0f);
count = Transpose(_outputBuffer.PtrEnd(sizeTemp), _tempBuffer.PtrBegin(), count);
_outputBuffer.PutSamples(count);
}
/// <summary>
/// Transposes sample rate by applying anti-alias filter to prevent
/// folding. Returns amount of samples returned in the
/// <see cref="_outputBuffer"/> buffer.
/// </summary>
private void ProcessSamples(ArrayPtr <TSampleType> src, int numSamples)
{
if (numSamples == 0)
{
return;
}
// Store samples to input buffer
_inputBuffer.PutSamples(src, numSamples);
// If anti-alias filter is turned off, simply transpose without applying
// the filter
if (!_useAliasFilter)
{
int count = _transposer.Transpose(_outputBuffer, _inputBuffer);
return;
}
Debug.Assert(_antiAliasFilter != null);
// Transpose with anti-alias filter
if (_transposer.rate < 1.0f)
{
// If the parameter 'Rate' value is smaller than 1, first transpose
// the samples and then apply the anti-alias filter to remove aliasing.
// Transpose the samples, store the result to end of "midBuffer"
_transposer.Transpose(_midBuffer, _inputBuffer);
// Apply the anti-alias filter for transposed samples in midBuffer
_antiAliasFilter.Evaluate(_outputBuffer, _midBuffer);
}
else
{
// If the parameter 'Rate' value is larger than 1, first apply the
// anti-alias filter to remove high frequencies (prevent them from folding
// over the lover frequencies), then transpose.
// Apply the anti-alias filter for samples in inputBuffer
_antiAliasFilter.Evaluate(_midBuffer, _inputBuffer);
// Transpose the AA-filtered samples in "midBuffer"
_transposer.Transpose(_outputBuffer, _midBuffer);
}
}
