Tape recorder
A tape recorder, tape deck, cassette deck or tape machine records and plays back sound using magnetic tape for storage. It records a fluctuating signal by moving a strip of magnetic tape across a tape head.
Description of operation
Electrical part
1 - lever, moving the pressing wheel;
2 - rubber covered wheel, to press the tape to the leading wheel;
3 - flywheel (stabilises the tape traction speed);
4 - lover axis holder;
5 - leading wheel (determines the tape traction speed);
6 - spring;
7 - detail, pressing the tape to the magnetic heads;
8 - intermediate wheel;
9 - electric motor (one for both playing and tape rewinding);
10 - rewind activation control;
11 - 15 - tape traction speed selector;
16, 34 - cloth - covered surface to create the friction force, preserving the constant tension of the tape (stronger friction is required on the tape accepting side);
17, 30 - bottom side of the tape holder, rotates with the constant speed;
18, 32 - top side of the tape holder, rotation speed depends from the remaining amount of the tape;
19 - 22, 25, 28, 35 - belt gear to rotate the tape holders at reduced speed;
23 - erasing magnetic head;
24 - spring;
26 - brake;
21, 27, 31 - tape directors;
29 - the universal magnetic head, used both for playing and recording;
33 - pusher to apply the brakes;
36, 37 - additional levers;
38 - operating controls.
Current flowing in the coils of the electromagnet causes the magnetic material on the tape to align in a manner proportional to the original signal. The signal can be reproduced by running the tape back across the tape head, where the reverse process occurs - the magnetic imprint on the tape induces a small current in the read head which approximates the original signal. This is then amplified for playback. Many tape recorders are capable of recording and playing back at once by means of separate record and playback heads in line or combined in one unit.
Mechanical part
Professional recorders usually use a simple three-motor scheme. One motor with a constant rotation speed provides traction for the leading wheel. The leading wheel is usually combined with a flywheel to ensure that the tape speed does not fluctuate. The other two motors apply constant torque to maintain the tape's tension or wind the tape quickly. Cheaper models use a single motor for all required functions. There are also variants with two motors, in which one motor is used for rewinding only.
Limitations
The storage of an analogue signal on tape works well, but is not perfect. In particular, the granular nature of the magnetic material adds noise to the signal, which is usually heard as tape hiss. Also, the magnetic characteristics of tape are not linear. They exhibit a characteristic hysteresis curve, which causes unwanted distortion of the signal. Some of this distortion is overcome by using an inaudible high-frequency AC bias signal when recording, though the amount of bias needs careful adjustment for best results. Different tape material requires differing amounts of bias, which is why most recorders have a switch to select this (or switch automatically). Additionally, systems such as Dolby B and Dolby HX-Pro have been devised to ameliorate some of the noise and distortion problems. Variations in tape speed cause flutter, which can be reduced by using dual capstans.
Variety of tape recorders
There are a wide variety of tape recorders in existence, from small hand held devices to large multitrack machines. This multitrack technology enabled the development of modern art music and one such artist, Brian Eno, described the tape recorder as "an automatic musical collage device".
Use of tape recorders
An important use of tape recorders is the recording of video. Video cassette recorders differ substantially from audio recorders because of the use of a rotating magnetic head that uses a helical scan of the tape medium. A helical scan is used to allow for faster movement of the tape surface over the head.
While they are primarily used for sound recording, tape machines were also important for data storage before the advent of floppy disks and CDs, and are still used today, although primarily to provide an offline backup to hard disk drives.