in sound reproduction, waver in a reproduced tone or group of tones that is caused by irregularities in turntable or tape drive speed during recording, duplication, or reproduction. Low-frequency irregularities (as one per revolution of a turntable, referred to as “once arounds”) cause wow and are recognized aurally as fluctuations in pitch. Irregularities that occur at higher frequencies are called flutter and cause a roughening of the tone: a piano sounds like a harp, and voices waver with small, rapid variations above and below proper pitch. Included among the causes of flutter and wow in disks are high spots in drive rollers and an off-centre hole in the disk. In tape and film reproducers, characteristic causes include nonuniform tension in take-up and payoff reels and mechanical distortion of the tape. Low-frequency background noise, either recorded on disk or tape from the recording mechanism or added to the reproduced tone from the reproducing mechanism, is known as rumble and is usually the result of vibration of the drive mechanism.