Equalization for Tape Playback

When a magnetic image of a sound signal is recorded onto tape with optimum bias, the magnetization of the tape is linearly proportional to the signal voltage applied to the head.

The playback process, depends not only upon the magnetization of the tape which passes under the playback head but also upon its frequency. By Faraday's law:

The output signal voltage then increases by a factor of two for each octave rise in frequency f, so an equalization circuit must be employed to reduce the signal back to proper balance. A factor of two in voltage is 6 decibels in power, so the equalization circuit must increase its attenuation 6 dB per octave.

Iron and Chromium Comparison

Phonograph Cartridge

The movement of a coil of wire in a magnetic field generates a voltage according to Faraday's law. The tracking of a groove on a vinyl record by the needle on a phonograph cartridge may cause a tiny coil to move in a magnetic field, generating an electrical image of the signal recorded in the groove. 线圈在磁场中的运动根据法拉第定律会产生电压。 phonograph cartridge 上的针跟踪 vinyl 比例上的沟槽可能会使一个微小的线圈在磁场中移动，从而生成信号的电信号。

Other types of cartridges may use moving magnets in a coil. A stereo record has different signals on the two sides of the groove, moving the needle in perpendicular directions so that they can be separated by perpendicular coils. 其他类型的 cartridge 可能使用线圈中的移动磁铁。立体声唱片的沟槽两侧有不同的信号，使针头在垂直方向上移动，从而可以通过垂直的线圈分开。