diff --git a/melbank.py b/melbank.py deleted file mode 100644 index 4badbcc..0000000 --- a/melbank.py +++ /dev/null @@ -1,151 +0,0 @@ -"""This module implements a Mel Filter Bank. -In other words it is a filter bank with triangular shaped bands -arnged on the mel frequency scale. -An example ist shown in the following figure: -.. plot:: - from pylab import plt - import melbank - f1, f2 = 1000, 8000 - melmat, (melfreq, fftfreq) = melbank.compute_melmat(6, f1, f2, num_fft_bands=4097) - fig, ax = plt.subplots(figsize=(8, 3)) - ax.plot(fftfreq, melmat.T) - ax.grid(True) - ax.set_ylabel('Weight') - ax.set_xlabel('Frequency / Hz') - ax.set_xlim((f1, f2)) - ax2 = ax.twiny() - ax2.xaxis.set_ticks_position('top') - ax2.set_xlim((f1, f2)) - ax2.xaxis.set_ticks(melbank.mel_to_hertz(melfreq)) - ax2.xaxis.set_ticklabels(['{:.0f}'.format(mf) for mf in melfreq]) - ax2.set_xlabel('Frequency / mel') - plt.tight_layout() - fig, ax = plt.subplots() - ax.matshow(melmat) - plt.axis('equal') - plt.axis('tight') - plt.title('Mel Matrix') - plt.tight_layout() -Functions ---------- -""" - -from numpy import abs, append, arange, insert, linspace, log10, round, zeros - - -def hertz_to_mel(freq): - """Returns mel-frequency from linear frequency input. - Parameter - --------- - freq : scalar or ndarray - Frequency value or array in Hz. - Returns - ------- - mel : scalar or ndarray - Mel-frequency value or ndarray in Mel - """ - return 2595.0 * log10(1 + (freq / 700.0)) - - -def mel_to_hertz(mel): - """Returns frequency from mel-frequency input. - Parameter - --------- - mel : scalar or ndarray - Mel-frequency value or ndarray in Mel - Returns - ------- - freq : scalar or ndarray - Frequency value or array in Hz. - """ - return 700.0 * (10**(mel / 2595.0)) - 700.0 - - -def melfrequencies_mel_filterbank(num_bands, freq_min, freq_max, num_fft_bands): - """Returns centerfrequencies and band edges for a mel filter bank - Parameters - ---------- - num_bands : int - Number of mel bands. - freq_min : scalar - Minimum frequency for the first band. - freq_max : scalar - Maximum frequency for the last band. - num_fft_bands : int - Number of fft bands. - Returns - ------- - center_frequencies_mel : ndarray - lower_edges_mel : ndarray - upper_edges_mel : ndarray - """ - - mel_max = hertz_to_mel(freq_max) - mel_min = hertz_to_mel(freq_min) - delta_mel = abs(mel_max - mel_min) / (num_bands + 1.0) - frequencies_mel = mel_min + delta_mel * arange(0, num_bands + 2) - lower_edges_mel = frequencies_mel[:-2] - upper_edges_mel = frequencies_mel[2:] - center_frequencies_mel = frequencies_mel[1:-1] - return center_frequencies_mel, lower_edges_mel, upper_edges_mel - - -def compute_melmat(num_mel_bands=12, freq_min=64, freq_max=8000, - num_fft_bands=513, sample_rate=16000): - """Returns tranformation matrix for mel spectrum. - Parameters - ---------- - num_mel_bands : int - Number of mel bands. Number of rows in melmat. - Default: 24 - freq_min : scalar - Minimum frequency for the first band. - Default: 64 - freq_max : scalar - Maximum frequency for the last band. - Default: 8000 - num_fft_bands : int - Number of fft-frequenc bands. This ist NFFT/2+1 ! - number of columns in melmat. - Default: 513 (this means NFFT=1024) - sample_rate : scalar - Sample rate for the signals that will be used. - Default: 44100 - Returns - ------- - melmat : ndarray - Transformation matrix for the mel spectrum. - Use this with fft spectra of num_fft_bands_bands length - and multiply the spectrum with the melmat - this will tranform your fft-spectrum - to a mel-spectrum. - frequencies : tuple (ndarray , ndarray ) - Center frequencies of the mel bands, center frequencies of fft spectrum. - """ - center_frequencies_mel, lower_edges_mel, upper_edges_mel = \ - melfrequencies_mel_filterbank( - num_mel_bands, - freq_min, - freq_max, - num_fft_bands - ) - - center_frequencies_hz = mel_to_hertz(center_frequencies_mel) - lower_edges_hz = mel_to_hertz(lower_edges_mel) - upper_edges_hz = mel_to_hertz(upper_edges_mel) - freqs = linspace(0.0, sample_rate / 2.0, num_fft_bands) - melmat = zeros((num_mel_bands, num_fft_bands)) - - for imelband, (center, lower, upper) in enumerate(zip( - center_frequencies_hz, lower_edges_hz, upper_edges_hz)): - - left_slope = (freqs >= lower) == (freqs <= center) - melmat[imelband, left_slope] = ( - (freqs[left_slope] - lower) / (center - lower) - ) - - right_slope = (freqs >= center) == (freqs <= upper) - melmat[imelband, right_slope] = ( - (upper - freqs[right_slope]) / (upper - center) - ) - return melmat, (center_frequencies_mel, freqs)