The Audio Cassette

The Compact Cassette is a magnetic tape sound recorder format. Although originally designed for dictation, improvements in fidelity led the Compact Cassette to supplant reel-to-reel tape recording in most non-professional applications. Its uses ranged from portable audio to home recording to data storage for early microcomputers. Between the early 1970s and late 1990s, the cassette was one of the two most common formats for prerecorded music, first alongside the LP and later the Compact Disc.

Compact Cassettes consist of two miniature spools, between which a magnetically coated plastic tape is passed and wound. These spools and their attendant parts are held inside a protective plastic shell. Two stero pairs of tracks (four total) or two monoaural audio tracks are available on the tape; one stereo pair or one monophonic track is played or recorded when the tape is moving in one direction and the second pair when moving in the other direction. This reversal is achieved either by manually flipping the cassette or by having the machine itself change the direction of tape movement ("auto-reverse")

The cassette was a great step forward in convenience from reel-to-reel audio tape recording, though because of the limitations of the cassette's size and speed, it initially compared poorly in quality. This permitted monaural cassette players to play stereo recordings "summed" as mono tracks and permitted stereo players to play mono recordings through both speakers. The tape is 3.81 mm wide, with each stereo track 0.6 mm wide and an unrecorded guard band between each track. The tape moves at 4.76 cm/s from left to right. For comparison, the typical open reel format in consumer use was ¼ inch wide, each stereo track nominally 1.59 mm wide, and running at either 9.5 or 19 cm/s.

Tape length is usually measured in minutes of total playing time. The most popular varieties are C46 (23 minutes per side), C60 (30 minutes per side), C90, and C120. The C46 and C60 lengths are typically 15–16 µm thick, but C90s are 10–11 µm and C120s are just 9 µm thick, rendering them more susceptible to stretching or breakage. Some vendors are more generous than others, providing 132 meters or 135 meters rather than 129 meters of tape for a C90 cassette. C180 and even C240 tapes were available at one time, but these were extremely thin and fragile and suffered badly from effects such as print-through, which made them unsuitable for general use.

Cassette types

• Type I - Ferric Oxide (Fe₂O₃)
• Type II - Chromium Oxide (CrO₂)
• Type III - Ferrichrome (FeCr)
• Type IV - Metall