تسجيل الشريط والاسطوانات المجسمة - الاستجابة الترددية للتسجيل .. الإلكترونيات

Tape and CD recording - Frequency response of recording.. Electronics

Tape and CD recording

Recording tapes are widely used in television recording or video recording, and are also used to store information inside electronic computers, and for other uses

In audio recording, the signal intensity level is raised to the required power for recording by an audio amplifier (181), then its output is taken to the recording head, which consists of coils surrounding an iron core containing a narrow air gap. It must be noted that the passage of audio signals through the coil causes noticeable changes in the intensity of the magnetic field generated in this gap. The recording tape is made of polyvinyl chloride, or any other insulating material, coated with very small iron oxide particles, and the width of the audio tape is 4/1 inch, while the width of the video tape is 12 inches.

181 - Amplification and the recording head.

Before the recording process, the iron oxide particles on the tape are randomly distributed on its surface (182). During the recording process, a mechanism pulls the tape in front of the air gap of the recording head, where the iron particles are arranged, magnetized, and aligned in a specific way so that magnetized areas are formed on the tape, the intensity of which varies according to the intensity of the magnetic current in the recording head coils. To increase the recording time, it is usually preferable to divide the tape into two tracks so that recording is done on one of them, then the tape position is reversed to allow recording on the other half. Sometimes it is preferable to divide the tape into four tracks.

Frequency response of recording

If we assume that the tape is moving at a speed of 15 inches per second, and what is recorded on the tape is an audio tone with a frequency of 15 vibrations per second, the distance between one peak and the next is one inch. However, if the tape speed is 7.5 inches per second, this distance becomes only half an inch. We can say that this distance decreases as the tape speed decreases (183) Raising the audio frequency level leads to the magnetic sections on the tape getting closer and closer.

182 - Magnetic recording on tape.

But there is a minimum that cannot be exceeded, and that is when the length of the magnetic sector corresponding to the distance between one vibration and another becomes smaller than the hole of the recording head. Then, the recording results are not useful and this can be avoided by using heads with very small air gaps, reaching approximately 0.000025 inches. It is also preferable, when recording music or any audio signal with a vibration of 10,000 vibrations per second, that the tape speed not be less than 15 inches per second. However, in the case of recording less sensitive audio signals, it is preferable to reduce the recording speed until it becomes between 7.5 and 3.75 inches per second. In the case of recording only speech, much lower recording speeds are used, i.e. 1 inch and 7/8 inch per second.

Thus, we can extend the recording time on the tape without the need to use large quantities of it. Dividing the tape into two or more wires will also give a longer time.

183 - Tape speed and its response to the signal frequency.
184 - Tape drive mechanism.