With synchronous disturbance or flutter (English wow and flutter ) refers to the speed fluctuations during recording and playback of analog recordings such as records , tapes or compact cassettes that are triggered by a speed fluctuation of the drive system. Reasons for this are, for example, voltage fluctuations in the power supply, wear of drive belts or friction wheels and acceleration forces acting on the device due to vibrations. Synchronization disturbances are noticed by the average hearing from 0.2 ... 0.3% and above a certain strength lead to audible fluctuations in pitch , which are perceived as "lyres", "yelps" or "whimpers". The hi-fi standard DIN 45500 allows a maximum wow and flutter of 0.2%. Modern devices achieve values of 0.02% to 0.08% thanks to quartz-controlled motors. Digital storage media are insensitive to mechanical synchronism disturbances. However, there is a comparable effect that is caused by irregularities in the clock frequency ( sampling frequency ). This error is called jitter . Two image disturbances of this type are exemplarily presented in the compendium of image disturbances in analog video (2013), based on a video by Jean Otth René Berger - Video Portrait from 1975.