Tape transport

The tape head is set off-center in a multitrack device in order to record or play one or more tracks running in each direction of the tape (e.g. the two different tracks present on most, if not all, compact cassettes).

Capstans are precision-machined spindles, and polished very smooth: any out-of-roundness or imperfections can cause uneven motion and an audible effect called flutter.

The alternative to capstan drive, simply driving the tape takeup reel (which was used on some cheap tape recorders), causes problems both with the speed difference between a full and empty reel and with speed variations as described.

The pinch roller is a rubberized, free-spinning wheel typically used to press magnetic tape against a capstan shaft in order to create friction necessary to drive the tape along the magnetic heads (erase, write, read).

An example of the application of multiple pinch rollers is the Technics RS-1520 tape recorder, which utilizes two pinch rollers located on opposite sides of a single capstan shaft, providing a more stable transport across two sets of magnetic heads.