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Computes MFCCs of log_mel_spectrograms
.
tf.signal.mfccs_from_log_mel_spectrograms(
log_mel_spectrograms, name=None
)
Implemented with GPU-compatible ops and supports gradients.
Mel-Frequency Cepstral Coefficient (MFCC) calculation consists of taking the DCT-II of a log-magnitude mel-scale spectrogram. HTK's MFCCs use a particular scaling of the DCT-II which is almost orthogonal normalization. We follow this convention.
All num_mel_bins
MFCCs are returned and it is up to the caller to select
a subset of the MFCCs based on their application. For example, it is typical
to only use the first few for speech recognition, as this results in
an approximately pitch-invariant representation of the signal.
For example:
batch_size, num_samples, sample_rate = 32, 32000, 16000.0
# A Tensor of [batch_size, num_samples] mono PCM samples in the range [-1, 1].
pcm = tf.random.normal([batch_size, num_samples], dtype=tf.float32)
# A 1024-point STFT with frames of 64 ms and 75% overlap.
stfts = tf.signal.stft(pcm, frame_length=1024, frame_step=256,
fft_length=1024)
spectrograms = tf.abs(stfts)
# Warp the linear scale spectrograms into the mel-scale.
num_spectrogram_bins = stfts.shape[-1].value
lower_edge_hertz, upper_edge_hertz, num_mel_bins = 80.0, 7600.0, 80
linear_to_mel_weight_matrix = tf.signal.linear_to_mel_weight_matrix(
num_mel_bins, num_spectrogram_bins, sample_rate, lower_edge_hertz,
upper_edge_hertz)
mel_spectrograms = tf.tensordot(
spectrograms, linear_to_mel_weight_matrix, 1)
mel_spectrograms.set_shape(spectrograms.shape[:-1].concatenate(
linear_to_mel_weight_matrix.shape[-1:]))
# Compute a stabilized log to get log-magnitude mel-scale spectrograms.
log_mel_spectrograms = tf.math.log(mel_spectrograms + 1e-6)
# Compute MFCCs from log_mel_spectrograms and take the first 13.
mfccs = tf.signal.mfccs_from_log_mel_spectrograms(
log_mel_spectrograms)[..., :13]
Args | |
---|---|
log_mel_spectrograms
|
A [..., num_mel_bins] float32 /float64 Tensor
of log-magnitude mel-scale spectrograms.
|
name
|
An optional name for the operation. |
Returns | |
---|---|
A [..., num_mel_bins] float32 /float64 Tensor of the MFCCs of
log_mel_spectrograms .
|
Raises | |
---|---|
ValueError
|
If num_mel_bins is not positive.
|