Audio Fundamentals
Wow and flutter describe slow and fast variations in playback speed that cause pitch instability in analogue recording and playback systems. Wow refers to slower, cyclic pitch changes, while flutter refers to faster, more rapid fluctuations.
Wow and flutter are forms of time-based distortion found in analogue media such as tape machines, vinyl turntables, and film sound reproducers. They occur when the speed of the recording or playback mechanism is not perfectly constant, causing the reproduced frequency (pitch) of the audio signal to drift over time.
Wow is the slower component, typically below 6 Hz, resulting in audible wavering or detuning of sustained notes. It often arises from mechanical imperfections like eccentric tape reels, uneven capstan rotation, or out-of-round turntable platters.
Flutter refers to faster speed variations, usually between about 6 Hz and 100 Hz, which can make the audio sound rough, unstable, or phasey. Common causes include motor vibration, worn pinch rollers, misaligned bearings, or variations in tape tension.
Wow and flutter are measured as a percentage or in parts per million (ppm) of speed deviation, using weighted standards such as DIN 45507 or IEC 386. High-precision professional tape recorders, such as those from Studer or Ampex, typically achieve figures below 0.04 %, while consumer or cassette machines may measure 0.1 % or higher.
In practical terms, wow and flutter reduce the pitch stability and perceived fidelity of analogue recordings. Though digital systems have largely eliminated these errors, the terms remain important in describing mechanical performance and the historical limitations of analogue audio technology.
