Wow and Flutter Measurement - Absolute Speed

Absolute Speed

Absolute speed error causes a change in pitch, and it is useful to know that a semitone in music represents a 6% frequency change. 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. Anyone with a good musical ear can detect a pitch change of around 1%, though an error of up to 3% is likely to go unnoticed, except by those few with ‘absolute pitch’. Most ‘movie’ films shown on European television are sped up by 4.166% because they were shot at 24 frames per second, but are scanned at 25 frames per second to match the PAL standard of 25 frame/s 50 field/s. 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 can also frustrate attempts to play along with film music, which is closer to a semitone sharp than its intended pitch. Recently, digital pitch correction has been applied to some films, which corrects the pitch without altering lip-sync, by adding in extra cycles of sound. This has to be regarded as a form of distortion, as there is no way to change the pitch of a sound without also slowing it down that does not change the waveform itself.