static LPair<S, BWImage> recordingFrequencyImagesWithWords(F1<S, Bool> wordFilter) {
  LPair<S, BWImage> images = new L;
  L<File> files = audioRecordingsWithSingleClip();
  for (File f : allRecordings()) {
    S word = wordFromAudioFileName(f);
    if (!isTrue(callF(wordFilter, word))) continue;
    images.add(pair(word, bwAutoContrast(audio_defaultClip(audioFileToFrequencyImage(f)))));
    print(fileName(f));
  }
  ret images;
}