Magnetic Recording/Audiocassette

In an audiocassette player, the tape must move from the supply reel to the take-up reel at constant speed. Otherwise the sound becomes distorted. It would not work to pull the tape along simply by rotating the take-up reel, because each successive revolution would pull a longer section of tape past the heads, causing the tape speed to increase.

To obtain a constant tape speed, a motor is used to turn a small metal cylinder, called a capstan, at constant speed. When the tape player is switched on, a roller presses the tape against the rotating capstan. The tape is pinched between the roller and capstan, forcing it to move toward the take-up reel at constant speed, as desired.

The main problem with this tape drive mechanism is that it may generate a background hum in the output sound. One can listen for hum by playing a tape that is blank and turning the volume control up to maximum. This provides a helpful comparison test when trying out several models in an audio store for possible purchase.