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The Effects of Wow, Flutter, and Rumble

Author: N.H. Crowhurst

No matter which type of recording is used, constant speed drive is a vital necessity, both for making and for playing back the recording. Variation in speed not only changes the rate at which the program is recorded or reproduced, but also changes its pitch or frequency. Turning a phonograph record faster raises all the frequencies by the same ratio, and the pitch steps up by a constant tone interval. While it is important to have the right speed, it is more important for the right speed to be steady. It must not warble up and down, or flutter up and down.

If a phonograph record is not mounted true, this will result in change in speed along the groove, which will cause pitch to vary once per revolution, an effect called wow. Wow can also be caused by variation in bearing friction as the turntable goes around. Variations in speed at a greater speed than once per revolution are called flutter because of the effect they produce on the reproduction. These effects can happen equally well to optical or magnetic recording, so careful mechanical design, to prevent any nonuniformity of speed, is needed with any recording drive.

The turntable

An effect most noticeable on phonograph recording, but entirely exclusive to it, is- called rumble. This is caused by mechanical vibration in the turntable. The pickup stylus will be moved just as much by the whole groove vibrating as by vibrations that occur in the groove as it passes. Consequently any motor vibration that gets to the turntable will appear in the reproduction as rumble.

Last Update: 2010-11-03