How Tape Recorders Work

Tape Types and Bias

Most higher-end tape decks have controls like those below for different tape formulations and bias.

Most higher-quality tapes tell you their formulation by stating a type. There are four types of tape in common use today:

  • Type 0 - This is the original ferric-oxide tape. It is very rarely seen these days.
  • Type 1 - This is standard ferric-oxide tape, also referred to as "normal bias."
  • Type 2 - This is "chrome" or CrO2 tape. The ferric-oxide particles are mixed with chromium dioxide.
  • Type 4 - This is "metal" tape. Metallic particles rather than metal-oxide particles are used in the tape.

Sound quality improves as you go from one type to the next, with metal tapes having the best sound quality. A normal tape deck cannot record onto a metal tape -- the deck must have a setting for metal tapes in order to record onto them. Any tape player can play a metal tape, however.

The controls on the tape deck let you match the recording bias and signal strength to the type of tape you are using so that you get the best sound possible.

Bias is a special signal that is applied during recording. The first tape recorders simply applied the raw audio signal to the electromagnet in the head. This works, but produces a lot of distortion on low-frequency sounds. A bias signal is a 100-kilohertz signal that is added to the audio signal. The bias moves the signal being recorded up into the "linear portion" of the tape's magnetization curve. This movement means that the tape reproduces the sound recorded on it more faithfully. Several of the links below go into this topic in detail, and also cover Dolby noise-reduction systems.

For more information on tape recorders, cassettes, magnetic recording and related topics, check out the links below.

Related HowStuffWorks Articles

More Great Links