MIR::StftFrameProvider Class Reference

#include <StftFrameProvider.h>

Collaboration diagram for MIR::StftFrameProvider:

Public Member Functions
	StftFrameProvider (const MirAudioReader &source)
bool	GetNextFrame (PffftFloatVector &frame)
int	GetNumFrames () const
int	GetSampleRate () const
double	GetFrameRate () const
int	GetFftSize () const

Private Attributes
const MirAudioReader &	mAudio
const int	mFftSize
const double	mHopSize
const std::vector< float >	mWindow
const int	mNumFrames
const long long	mNumSamples
int	mNumFramesProvided = 0

Detailed Description

Utility class to provide time-domain frames ready for FFT. The returned frames have power-of-two size and are already windowed with a Hann window, scaled such that it sums to unity. Also, GetNumFrames() is the closest power of two that satifsies a hop size of 10ms. This property facilitates the FFT analysis of transformation of the STFT frames to some scalar, e.g. the novelty values of an onset detection function.

Definition at line 28 of file StftFrameProvider.h.

Constructor & Destructor Documentation

StftFrameProvider()

MIR::StftFrameProvider::StftFrameProvider

(

const MirAudioReader &

source

)

Definition at line 46 of file StftFrameProvider.cpp.

    : mAudio { audio }
    , mFftSize { GetFrameSize(audio.GetSampleRate()) }
    , mHopSize { GetHopSize(audio.GetSampleRate(), audio.GetNumSamples()) }
    , mWindow { GetNormalizedHann(mFftSize) }
    , mNumFrames { mHopSize > 0 ? static_cast<int>(std::round(
                                     audio.GetNumSamples() / mHopSize)) :
                                  0 }
    , mNumSamples { audio.GetNumSamples() }
{
   assert(mNumFrames == 0 || IsPowOfTwo(mNumFrames));
}

References MIR::IsPowOfTwo(), and mNumFrames.

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Member Function Documentation

GetFftSize()

int MIR::StftFrameProvider::GetFftSize

(

)

const

Definition at line 100 of file StftFrameProvider.cpp.

{
   return mFftSize;
}

References mFftSize.

GetFrameRate()

double MIR::StftFrameProvider::GetFrameRate

(

)

const

Definition at line 95 of file StftFrameProvider.cpp.

{
   return 1. * mAudio.GetSampleRate() / mHopSize;
}

References MIR::MirAudioReader::GetSampleRate(), mAudio, and mHopSize.

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GetNextFrame()

bool MIR::StftFrameProvider::GetNextFrame

(

PffftFloatVector &

frame

)

Definition at line 59 of file StftFrameProvider.cpp.

{
   if (mNumFramesProvided >= mNumFrames)
      return false;
   frame.resize(mFftSize, 0.f);
   const int firstReadPosition = mHopSize - mFftSize;
   int start = std::round(firstReadPosition + mNumFramesProvided * mHopSize);
   while (start < 0)
      start += mNumSamples;
   const auto end = std::min<long long>(start + mFftSize, mNumSamples);
   const auto numToRead = end - start;
   mAudio.ReadFloats(frame.data(), start, numToRead);
   // It's not impossible that some user drops a file so short that `mFftSize >
   // mNumSamples`. In that case we won't be returning a meaningful
   // STFT, but that's a use case we're not interested in. We just need to make
   // sure we don't crash.
   const auto numRemaining = std::min(mFftSize - numToRead, mNumSamples);
   if (numRemaining > 0)
      mAudio.ReadFloats(frame.data() + numToRead, 0, numRemaining);
   std::transform(
      frame.begin(), frame.end(), mWindow.begin(), frame.begin(),
      std::multiplies<float>());
   ++mNumFramesProvided;
   return true;
}

References details::end(), mAudio, mFftSize, mHopSize, min(), mNumFrames, mNumFramesProvided, mNumSamples, mWindow, MIR::MirAudioReader::ReadFloats(), and fast_float::round().

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GetNumFrames()

int MIR::StftFrameProvider::GetNumFrames

(

)

const

Definition at line 85 of file StftFrameProvider.cpp.

{
   return mNumFrames;
}

References mNumFrames.

GetSampleRate()

int MIR::StftFrameProvider::GetSampleRate

(

)

const

Definition at line 90 of file StftFrameProvider.cpp.

{
   return mAudio.GetSampleRate();
}

References MIR::MirAudioReader::GetSampleRate(), and mAudio.

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Member Data Documentation

mAudio

const MirAudioReader& MIR::StftFrameProvider::mAudio

private

Definition at line 39 of file StftFrameProvider.h.

Referenced by GetFrameRate(), GetNextFrame(), and GetSampleRate().

mFftSize

const int MIR::StftFrameProvider::mFftSize

private

Definition at line 40 of file StftFrameProvider.h.

Referenced by GetFftSize(), and GetNextFrame().

mHopSize

const double MIR::StftFrameProvider::mHopSize

private

Definition at line 41 of file StftFrameProvider.h.

Referenced by GetFrameRate(), and GetNextFrame().

mNumFrames

const int MIR::StftFrameProvider::mNumFrames

private

Definition at line 43 of file StftFrameProvider.h.

Referenced by GetNextFrame(), GetNumFrames(), and StftFrameProvider().

mNumFramesProvided

int MIR::StftFrameProvider::mNumFramesProvided = 0

private

Definition at line 45 of file StftFrameProvider.h.

Referenced by GetNextFrame().

mNumSamples

const long long MIR::StftFrameProvider::mNumSamples

private

Definition at line 44 of file StftFrameProvider.h.

Referenced by GetNextFrame().

mWindow

const std::vector<float> MIR::StftFrameProvider::mWindow

private

Definition at line 42 of file StftFrameProvider.h.

Referenced by GetNextFrame().

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

• StftFrameProvider.h
• StftFrameProvider.cpp