The following example converts a single MP3 file to WAV (convert-to-wav), ensures that it is monophonic (convert-to-mono) and resamples it to 11khz (resample-audio) before saving it.

wai-annotations convert \
  from-audio-files-ac \
    -i "/some/where/an.mp3" \
  convert-to-wav \
  convert-to-mono \
  resample-audio \
    --sample-rate 11000 \
  to-audio-files-ac \
    -o /some/where/else/

When splitting up samples into sub-samples (automatically or by a human), it can happen quite often that there is silence at the start and/or at the end of the clip. The trim-audio plugin can be used to remove these (the minimum decibel level can be supplied as parameter):

wai-annotations convert \
  from-audio-files-ac \
    -i "/some/where/an.mp3" \
  convert-to-wav \
  convert-to-mono \
  resample-audio \
    --sample-rate 11000 \
  to-audio-files-ac \
    -o /some/where/else/

Audio augmentation is possible as well. The pitch-shift plugin changes the pitch of the sample and time-stretch can slow down or speed up the sample (using -T 0 for the threshold means it gets always applied):

wai-annotations convert \
  from-audio-files-ac \
    -i "/some/where/a.wav" \
  pitch-shift \
    -m add \
    -f 4 \
    -t 4 \
    -T 0 \
  time-stretch\
    -m add \
    -f 0.5 \
    -t 2.0 \
    -T 0 \
  to-audio-files-ac \
    -o /some/where/else/

Spectrograms from the audio samples can be generated using the stft-spectrogram and mel-spectrogram plugins:

wai-annotations convert \
  from-audio-files-ac \
    -i "/some/where/a.wav" \
  stft-spectrogram \
  to-images-ic \
    -o /some/where/else/

If the wai.annotations.generic module is installed, then it is possible to take advantage of the wai.annotations.audio.source.urban8k.Urban8k example class for loading the Urban8k. Using the wai.annotations.subdir module, the .wav files can be stored in sub-directories according to their class labels:

wai-annotations convert \
  generic-source-ac \
    -c "wai.annotations.audio.source.urban8k.Urban8k" \
    -o "--metadata-csv /some/where/UrbanSound8K/metadata/UrbanSound8K.csv --fold-dir /some/where/UrbanSound8K/audio/" \
  to-subdir-ac \
    -o /some/where/else/urban8k