Gaps - segments in a recording which represent unexplained changes in content or context. A gap can contain buzzing, humming, or silence. Transients - short, abrupt sounds exemplified by clicks, pops, etc. Transients may indicate tape splicing. Fades - gradual loss of volume.
Fades can cause inaudibility and are considered gaps when the recording becomes fully inaudible.
Equipment Sounds - inconsistencies of context caused by the recording equipment itself. Common equipment sounds include hums, static, whistles, and varying pitches. Extraneous Voices - background voices which at times appear to be near as the primary voices. These can at times even block the primary voices. The forensic scientist listens with proper headphones to the original tape using high quality analytical equipment.