Wow & Flutter

A cyclical variation in replay speed which affects the pitch of the recorded material. Wow is a low-speed variation (nominally below 4Hz) which typically occurs once per revolution of the device and may be caused by an off-centre hole on a vinyl record, or a sticking tape on a reel-reel machine. Flutter is a higher speed variation (nomninally above 4Hz) and can often be perceived as a form of intermodulation distortion.