Wow and flutter measurement

This measurement quantifies the amount of 'frequency wobble' (caused by speed fluctuations) present in subjectively valid terms.

In digital systems, which are locked to crystal oscillators, variations in clock timing are referred to as wander or jitter, depending on speed.

The following standards all specify the weighting filter shown above, together with a special slow-quasi-peak full-wave rectifier designed to register any brief speed excursions.

Record-replay flutter will then be around twice as high as pre-recorded, because worst case variations will add during recording and playback.

Wow and flutter are particularly audible on music with oboe, string, guitar, flute, brass, or piano solo playing.

This may be due to the persistence of memory with regard to spatial location based on early reflections and comparison of Doppler effects over time.

This is because Western music uses the ‘equal temperament scale' based on a constant geometric ratio between twelve notes; and the twelfth root of 2 is 1.05946.

This causes a noticeable increase in pitch on voices, which often brings surprised comment from the actors themselves when they hear their performance on video.

It adds a roughness to the sound that is not typical of wow & flutter, and damping devices or heavy rollers are sometimes employed on professional tape machines to reduce or prevent it.