Wow is a relatively slow variation in the frequency of reproduced sound caused by slow speed variations in records, tape recorders, etc. Pitch fluctuations of one or two per second are classified as wow, while faster variations are called flutter. In spec sheets wow is usually rated, along with flutter, as a percentage where the percentage is the percent of pitch deviation produced by these two phenomenon in the machine. In practice we have found wow and flutter specs to be more of a ballpark or relative measure. Machines can behave very differently depending upon the type of tape used or even environmental factors which can affect tape consistency. This is especially true with cassette type tapes where the tape shell’s interaction with the tape is a huge variable. Wow and flutter are almost never an issue in digital recorders because tape speed has no direct bearing on the pitch of the audio playback or recording.