MIR::DecimatingMirAudioReader Class Reference

Our MIR operations do not need the full 44.1 or 48kHz resolution typical of audio files. It may change in the future, if we start looking at chromagrams for example, but for now even a certain amount of aliasing isn't an issue. In fact, for onset detection, it may even be beneficial, since it preserves a trace of the highest frequency components by folding them down below the nyquist. Thus we can decimate the audio signal to a certain extent. This is fast and easy to implement, meanwhile reducing dramatically the amount of data and operations. More...

#include <DecimatingMirAudioReader.h>

Inheritance diagram for MIR::DecimatingMirAudioReader:

Collaboration diagram for MIR::DecimatingMirAudioReader:

Public Member Functions
	DecimatingMirAudioReader (const MirAudioReader &reader)
double	GetSampleRate () const override
long long	GetNumSamples () const override
void	ReadFloats (float *buffer, long long start, size_t numFrames) const override
Public Member Functions inherited from MIR::MirAudioReader
virtual double	GetSampleRate () const =0
virtual long long	GetNumSamples () const =0
virtual void	ReadFloats (float *buffer, long long where, size_t numFrames) const =0
double	GetDuration () const
virtual	~MirAudioReader ()=default

Private Attributes
const MirAudioReader &	mReader
const int	mDecimationFactor
std::vector< float >	mBuffer

Detailed Description

Our MIR operations do not need the full 44.1 or 48kHz resolution typical of audio files. It may change in the future, if we start looking at chromagrams for example, but for now even a certain amount of aliasing isn't an issue. In fact, for onset detection, it may even be beneficial, since it preserves a trace of the highest frequency components by folding them down below the nyquist. Thus we can decimate the audio signal to a certain extent. This is fast and easy to implement, meanwhile reducing dramatically the amount of data and operations.

Definition at line 29 of file DecimatingMirAudioReader.h.

Constructor & Destructor Documentation

DecimatingMirAudioReader()

MIR::DecimatingMirAudioReader::DecimatingMirAudioReader ( const MirAudioReader &  reader )

explicit

Definition at line 18 of file DecimatingMirAudioReader.cpp.

    : mReader { reader }
    , mDecimationFactor {
       // Input rate divided by this integer will be as close as possible to
       // 24kHz and not greater.
       static_cast<int>(std::ceil(reader.GetSampleRate() / 24000.))
    }
{
}

Member Function Documentation

GetNumSamples()

long long MIR::DecimatingMirAudioReader::GetNumSamples ( ) const

overridevirtual

Implements MIR::MirAudioReader.

Definition at line 33 of file DecimatingMirAudioReader.cpp.

{
   // Return the floor
   return mReader.GetNumSamples() / mDecimationFactor;
}

References MIR::MirAudioReader::GetNumSamples(), mDecimationFactor, and mReader.

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GetSampleRate()

double MIR::DecimatingMirAudioReader::GetSampleRate ( ) const

overridevirtual

Implements MIR::MirAudioReader.

Definition at line 28 of file DecimatingMirAudioReader.cpp.

{
   return 1. * mReader.GetSampleRate() / mDecimationFactor;
}

References MIR::MirAudioReader::GetSampleRate(), mDecimationFactor, and mReader.

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ReadFloats()

void MIR::DecimatingMirAudioReader::ReadFloats ( float *  buffer, long long  start, size_t  numFrames  ) const

overridevirtual

Implements MIR::MirAudioReader.

Definition at line 39 of file DecimatingMirAudioReader.cpp.

{
   const auto numFrames = numDecimatedFrames * mDecimationFactor;
   if (mBuffer.size() < numFrames)
      mBuffer.resize(numFrames);
   const auto start = decimatedStart * mDecimationFactor;
   mReader.ReadFloats(mBuffer.data(), start, numFrames);
   for (auto i = 0; i < numDecimatedFrames; ++i)
      decimated[i] = mBuffer[i * mDecimationFactor];
}

References mBuffer, mDecimationFactor, mReader, and MIR::MirAudioReader::ReadFloats().

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Member Data Documentation

mBuffer

std::vector<float> MIR::DecimatingMirAudioReader::mBuffer

mutableprivate

Definition at line 42 of file DecimatingMirAudioReader.h.

Referenced by ReadFloats().

mDecimationFactor

const int MIR::DecimatingMirAudioReader::mDecimationFactor

private

Definition at line 41 of file DecimatingMirAudioReader.h.

Referenced by GetNumSamples(), GetSampleRate(), and ReadFloats().

mReader

const MirAudioReader& MIR::DecimatingMirAudioReader::mReader

private

Definition at line 40 of file DecimatingMirAudioReader.h.

Referenced by GetNumSamples(), GetSampleRate(), and ReadFloats().

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The documentation for this class was generated from the following files:

• DecimatingMirAudioReader.h
• DecimatingMirAudioReader.cpp