sub_bin_spec_analyzer.py

"""
Created 12-26-17 by Matthew C. McCallum
"""

import numpy as np


class SubBinSpecAnalyzer( object ):
    """
    An analyzer for re-estimating magnitude and phase between integer bin indices in
    a spectrogram.
    """

    def __init__( self, fft_size, window, resolution_mult ):
        """
        Constructor.

        Args:
            fft_size -> int - The FFT size used for analysis of any magnitudes and phases
            this class wishes to re-estimate.

            window -> np.ndarray - A 1D array containing the STFT analysis window used for
            any magnitudes or phases this class wishes to re-estimate.

            resolution_mult -> int - The number of intervals between each STFT bin that this
            class uses as a lookup table to re-estimate magnitudes and phases. The higher this
            number is the more accurate it is to a point.
        """
        sub_bin_spec = np.fft.fft( window, fft_size*resolution_mult );
        self._subbin_resolution = resolution_mult
        self._subbin_mag = np.abs( sub_bin_spec )
        self._subbin_mag = np.concatenate( ( self._subbin_mag[:resolution_mult], self._subbin_mag[-resolution_mult:] ) )
        self._subbin_phase = np.angle( sub_bin_spec )
        self._subbin_phase = np.concatenate( ( self._subbin_phase[:resolution_mult], self._subbin_phase[-resolution_mult:] ) )
        self._win_energy = np.sum( window )

    def GetMag( self, bin_mags, bin_offsets ):
        """
        Re-estimate a set of magnitudes at a given non-integer offset from their original bin indices.

        Args:
            bin_mags - np.ndarray - An array of the bin magnitudes at integer DFT indices that are representative
            of a peak at a potentially non-integer index.

            bin_offsets - np.ndarray - An array of float offsets to re-estimate the magnitude of each of the bins provided
            in bin_mags at.
        """
        assert all( np.abs( bin_offsets ) < 1.0*( self._subbin_resolution-1 )/self._subbin_resolution ), 'Tried to get subbin accuracy outside of the range of the SubBinSpecAnalyzer.'
        indices = np.around( bin_offsets*self._subbin_resolution ).astype( 'int32' )
        return bin_mags/self._subbin_mag[indices]*self._win_energy

    def GetPhase( self, bin_phases, bin_offsets ):
        """
        Re-estimate a set of phases at a given non-integer offset from their original bin indices.

        Args:
            bin_mags - np.ndarray - An array of the bin phases at integer DFT indices that are representative
            of a peak at a potentially non-integer index.

            bin_offsets - np.ndarray - An array of float offsets to re-estimate the phase of each of the bins provided
            in bin_mags at.
        """
        assert all( np.abs( bin_offsets ) < 1.0*( self._subbin_resolution-1 )/self._subbin_resolution ), 'Tried to get subbin accuracy outside of the range of the SubBinSpecAnalyzer.'
        indices = np.around( bin_offsets*self._subbin_resolution ).astype( 'int32' )
        return bin_phases + self._subbin_phase[indices]