librosa: filters.mel: ValueError: operands could not be broadcast together with shapes (1,1025) (0,)

Description

I get an exception in filters.mel: ValueError: operands could not be broadcast together with shapes (1,201) (0,). In line lower = -ramps[i] / fdiff[i], where fdiff = array([], shape=(130, 0), dtype=float64).

The same problem was also reported here:

• https://github.com/rwth-i6/returnn/issues/132
• https://github.com/Rayhane-mamah/Tacotron-2/issues/321

Steps/Code to Reproduce

Example:

      audio = numpy.array([ 2.78090321e-03,  3.32838898e-03,  4.34225125e-03, ...,
                           -4.98423541e-05, -1.79219493e-04,  1.82329724e-04])
      sample_rate = 16000
      num_feature_filters =  40
      step_len = 0.01
      window_len =  0.025

      mfccs = librosa.feature.mfcc(
            audio, sr=sample_rate,
            n_mfcc=num_feature_filters,
            hop_length=int(step_len * sample_rate), n_fft=int(window_len * sample_rate))

Expected Results

It works. It has also worked in the past.

Actual Results

Exception:

  File "/u/zeyer/setups/librispeech/2018-02-26--att/returnn/GeneratingDataset.py", line 814, in _get_audio_features_mfcc
    line: mfccs = librosa.feature.mfcc(
            audio, sr=sample_rate,
            n_mfcc=num_feature_filters,
            hop_length=int(step_len * sample_rate), n_fft=int(window_len * sample_rate))
    locals:
      mfccs = <not found>
      librosa = <local> <module 'librosa' from '/u/zeyer/.local/lib/python3.6/site-packages/librosa/__init__.py'>
      librosa.feature = <local> <module 'librosa.feature' from '/u/zeyer/.local/lib/python3.6/site-packages/librosa/feature/__init__.py'>
      librosa.feature.mfcc = <local> <function mfcc at 0x7f98700e9488>
      audio = <local> array([ 2.78090321e-03,  3.32838898e-03,  4.34225125e-03, ...,
                             -4.98423541e-05, -1.79219493e-04,  1.82329724e-04]), len = 22912
      sr = <not found>
      sample_rate = <local> 16000
      n_mfcc = <not found>
      num_feature_filters = <local> 40
      hop_length = <not found>
      int = <builtin> <class 'int'>
      step_len = <local> 0.01
      n_fft = <not found>
      window_len = <local> 0.025
  File "/u/zeyer/.local/lib/python3.6/site-packages/librosa/feature/spectral.py", line 1299, in mfcc
    line: S = power_to_db(melspectrogram(y=y, sr=sr, **kwargs))
    locals:
      S = <local> None
      power_to_db = <global> <function power_to_db at 0x7f98700d1048>
      melspectrogram = <global> <function melspectrogram at 0x7f98700e9510>
      y = <local> array([ 2.78090321e-03,  3.32838898e-03,  4.34225125e-03, ...,
                         -4.98423541e-05, -1.79219493e-04,  1.82329724e-04]), len = 22912
      sr = <local> 16000
      kwargs = <local> {'hop_length': 160, 'n_fft': 400}
  File "/u/zeyer/.local/lib/python3.6/site-packages/librosa/feature/spectral.py", line 1391, in melspectrogram
    line: mel_basis = filters.mel(sr, n_fft, **kwargs)
    locals:
      mel_basis = <not found>
      filters = <global> <module 'librosa.filters' from '/u/zeyer/.local/lib/python3.6/site-packages/librosa/filters.py'>
      filters.mel = <global> <function mel at 0x7f98701338c8>
      sr = <local> 16000
      n_fft = <local> 400
      kwargs = <local> {}
  File "/u/zeyer/.local/lib/python3.6/site-packages/librosa/filters.py", line 247, in mel
    line: lower = -ramps[i] / fdiff[i]
    locals:
      lower = <not found>
      ramps = <local> array([[[ 0.00000000e+00, -4.00000000e+01, -8.00000000e+01, ...,
...                             [[ 4.67655199e+01,  6.76551987e+00..., len = 130, _[0]: {len = 1, _[0]: {len = 201}}
      i = <local> 0
      fdiff = <local> array([], shape=(130, 0), dtype=float64), len = 130, _[0]: {len = 0}
ValueError: operands could not be broadcast together with shapes (1,201) (0,)

Versions

In [6]: librosa.version.show_versions()
INSTALLED VERSIONS
------------------
python: 3.6.3 (default, Oct 25 2017, 11:03:15) 
[GCC 5.4.0 20160609]

librosa: 0.5.1

audioread: 2.1.5
numpy: 1.16.0
scipy: 1.1.0
scikit-learn: None
joblib: 0.11
decorator: 4.3.0
six: 1.11.0
resampy: 0.2.0

numpydoc: None
sphinx: None
sphinx_rtd_theme: None
sphinxcontrib-versioning: None
matplotlib: 2.1.0
numba: 0.35.0

>>> import platform; print(platform.platform())
Linux-4.4.0-53-generic-x86_64-with-debian-stretch-sid
>>> import sys; print("Python", sys.version)
Python 3.6.3 (default, Oct 25 2017, 11:03:15) 
[GCC 5.4.0 20160609]
>>> import numpy; print("NumPy", numpy.__version__)
NumPy 1.16.0
>>> import scipy; print("SciPy", scipy.__version__)
SciPy 1.1.0
>>> import librosa; print("librosa", librosa.__version__)
librosa 0.5.1