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better rounding error fix. The ratio goes through a relatively low-resolution

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fixed-point representation within SpeedChange (m_iDeltaFrames).
This commit is contained in:
Glenn Maynard
2006-12-27 05:40:00 +00:00
parent 1044552a6f
commit 65e6922aca
2 changed files with 24 additions and 13 deletions
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stepmania/src/RageSoundReader_PitchChange.cpp
+24 -12
View File
@@ -45,8 +45,31 @@ int RageSoundReader_PitchChange::Read( char *pBuf, int iFrames )
float fRate = GetStreamToSourceRatio();
if( m_pSpeedChange->NextReadWillStep() )
{
/* This is the simple way: */
// float fRequestedSpeedRatio = m_fSpeedRatio / m_fPitchRatio;
// m_pSpeedChange->SetSpeedRatio( fRequestedSpeedRatio );
// m_pResample->SetRate( m_fPitchRatio );
/*
* However, the speed changer has a granularity due to internal fixed-
* point math, and the actual ratio will be slightly different than what
* we tell it to use. The actual ratio used is fActualSpeedChangeRatio.
* Given
*
* fRequestedSpeedRatio = m_fSpeedRatio / m_fPitchRatio
*
* solve for m_fPitchRatio:
*
* fRequestedPitchRatio = m_fSpeedRatio / fRequestedSpeedRatio
*
* and compute the pitch ratio based on the actual speed ratio, rather than
* the requested speed ratio. This avoids excessive rounding error between
* the ratios of m_pSpeedChange and m_pResample.
*/
m_pSpeedChange->SetSpeedRatio( m_fSpeedRatio / m_fPitchRatio );
m_pResample->SetRate( m_fPitchRatio );
float fActualSpeedRatio = m_pSpeedChange->GetRatio();
float fRequestedPitchRatio = m_fSpeedRatio / fActualSpeedRatio;
m_pResample->SetRate( fRequestedPitchRatio );
}
/* If we just applied a new speed and it caused the ratio to change, return
@@ -57,17 +80,6 @@ int RageSoundReader_PitchChange::Read( char *pBuf, int iFrames )
return RageSoundReader_Filter::Read( pBuf, iFrames );
}
float RageSoundReader_PitchChange::GetStreamToSourceRatio() const
{
/* If m_fSpeedRatio is 1.0f and the underlying ratio is exactly 1.0,
* the ratio should be exactly 1. Rounding error prevents n * (1/n)
* from being exact. */
float fRatio = m_pSource->GetStreamToSourceRatio();
if( m_fSpeedRatio == 1.0f && fabsf(1.0f - fRatio) < 0.001f )
fRatio = 1.0f;
return fRatio;
}
bool RageSoundReader_PitchChange::SetProperty( const RString &sProperty, float fValue )
{
if( sProperty == "Rate" )
stepmania/src/RageSoundReader_PitchChange.h
-1
View File
@@ -15,7 +15,6 @@ public:
virtual int Read( char *pBuf, int iFrames );
virtual bool SetProperty( const RString &sProperty, float fValue );
virtual float GetStreamToSourceRatio() const;
void SetSpeedRatio( float fRatio ) { m_fSpeedRatio = fRatio; }
void SetPitchRatio( float fRatio ) { m_fPitchRatio = fRatio; }