HOW stereo Sound is recorded on a tape?

[Shahriar]

Hi

Does anybody know how the stereo sound is recorded on a tape?

ThanX in advance
Shahriar

[audioguru]

Tape? Like cassette tape?
I worked for Philips when we invented compact cassette tape and the recorders and players for it.

When the tape is recorded it is divided into 4 tracks. 2 tracks for each direction of the tape, left channel and right channel. You can change the direction of the tape and use a 4-track tape head, or turn the tape over and use a 2-track tape head. Each track of a tape head is a magnetic core with a small vertical gap that touches the tape and many turns of wire in a coil. The tape head must be at exactly 90 degrees right angle to the tape for best high frequency response and the same for each side of a 2-track system. Adjusting the angle of the head is called the azimuth alignment.

The iron oxide particles on a tape have magnetic hysteresis which causes distortion at low levels so a bias frequency of about 100kHz is added while recording to raise the level to the low distortion linear portion of magnetism of the particles.

Cassette tape runs past the head at a very slow speed so the playback level is low. Since it is low, the playback sound would have hiss noise at high audio frequencies so equalization is used during recording to boost the high audio frequencies, then reduce them back to normal while reducing hiss during playback. The low tape speed reduces high audio frequencies so less reduction is used during playback. The tape saturates at high levels which are usually low audio frequencies so equalization cuts them during recording then boosts them back to normal during playback.

Erasing a tape uses a separate erase head with a very high bias signal in it.

Type 1 ferric-oxide tape was the 1st to be used then better type 2 chromium tape was used which required a different bias and equalization setting. I don't remember seeing a type 3 tape but I have some type 4 metal tapes and my cassette recorder automatically sets the bias and equalization for each tape type that it senses.

Dolby and others invented noise reduction systems that further improved the sound of compact cassette recordings and their playback.

CDs (also invented by Philips) replaced the compact cassette then MP3 recordings became popular. ;D     

[Shahriar]

Dear Audioguru

You said each side of a tape is devided into 2 Track, One track for Left channel  and one track for Right Channel;

Then What happens when you put a tape which is recorded with a Stereo Recoder in a Mono Tape(those Simple Ones);

Does the Head of these players read just one track; If so, Everythings go wrong ???

[audioguru]

A mono tape head has a long gap that picks up both stereo tracks and adds their level if they have the same sound. Nothing goes wrong unless the azimuth is so far out of adjustment that high audio frequencies that are the same on each channel are cancelled. ;D

[Shahriar]

Dear Audioguru

ThanX very Much for your Always Complete and Patient Answers...

Shahriar