varispeed

Varispeed is a technique and, in some contexts, a feature of audio and film equipment that allows the speed of playback or recording to vary over time. In magnetic tape systems, varispeed is achieved by changing the tape transport rate, typically by altering the capstan motor drive. Because the pitch of recorded audio on tape is closely tied to playback speed, altering the speed raises or lowers pitch while also changing the length of the recording. In film, varispeed refers to varying the frame rate during shooting or projection to create slow-motion or fast-motion effects, often using equipment capable of different speeds.

In music production, varispeed enabled creative pitch shifts and time distortions, contributing to distinctive timbres and textures on classic analog recordings. Engineers could modulate the speed during playback or recording to produce subtle or dramatic pitch changes, sometimes yielding a warbling or bending effect. This technique also allowed experiments with timing and synchronization between tracks, as well as unique vocal or instrument characteristics obtained through tape saturation and transient alteration.

In film and video work, varispeed is used to manipulate motion to match artistic intent or narrative pacing, including slow motion or accelerated motion effects, sometimes combined with synchronized sound to achieve particular moods.

Varispeed originated with mid-20th-century magnetic tape and projection technologies and became widespread through the 1950s to 1970s. With digital audio and video, many varispeed effects are now achieved via software-based time-stretching and pitch-shifting, though the term remains used to describe vintage techniques and equipment.