A portable route-based machine data collector stores audio files to supplement associated machine performance data, such as vibration data. The audio files, which may include voice comments, audio segments of raw vibration data, or frequency-shifted components of the vibration data, are stored in the data collector as standard-format digital audio files and are later downloaded to a computer for further analysis. Test personnel can then replay the audio files for data analysis personnel to get second opinions regarding whether machine faults may be indicated by the recorded sounds. Also, audio files associated with normal and abnormal machine operation may be saved on the portable data collector and used as baselines or for training purposes. Verbal operating instructions may also be stored as audio files on the portable data collector for replay by test operators in the field. In a case where the portable data collector is an ultrasonic monitoring unit, frequency-shifted (audible) ultrasonic data may be stored in an audio file in association with non-shifted ultrasonic data.