- Ambient noise (e.g., rustling, line noise, interference)
- Noisy environments (e.g., streets, bars, restaurants, or other types of background noise)
- Speakers who are recorded from a distance (e.g., ambiguous, distant voices)
- Speakers with a strong non-American accent (e.g., British, Australian, Indian, Hispanic, and other non-American speakers)
- Interruptions in the recording (e.g., poor phone line, gaps in the audio)
- Disturbing sounds (e.g., audible typing on keyboard, rustling, sound of wind, sounds of breathing)
- Incidences of deterioration (e.g., deterioration of volume, high voices, sound cuts)
- Speakers who cannot be understood (e.g., mumbling, changes in volume, frequent overlapping of voices)
- Echoes (e.g., reverberation, the same sound can be heard twice)
- Quality (e.g., low sample/bit rate, poor conference line, recorded off speakers)
- Diction (e.g., poor pronunciation, speaking fast, unnatural pronunciation)
- Deep voices (e.g., hidden or blocked microphone, old recordings.
