Is the recorder easy to use? The working principle and structure of the recorder
(1) Frequency response
Frequency response simply refers to the frequency range of the signal that the recorder can pass when recording and projecting sound. The frequency response of general models is between 125~6300Hz, and the frequency response of a good recorder is between 30~1600Hz. The wider the frequency response range, the richer the high and low frequencies.
2. Jitter rate
The jitter rate refers to the instantaneous wave condition of the transport speed, measured in fractions of a percent (about 0.4%) ), the smaller the value, the better.
3. Signal-to-noise ratio
Signal-to-noise ratio refers to the ratio of useful signal to noise. The larger the ratio, the smaller the noise during playback, generally above 30Db.
4. Distortion degree
Distortion degree reflects the fidelity of the original sound after recording and playback. The smaller the distortion, the better. Generally, the whole channel is not more than 8%.
(2) The working principle and structure of the tape recorder
The tape recorder is mainly used for sound recording and playback. There are two types of tapes and cassettes. Cassette recorders are widely used in the field of education because of their easy recording and playback operation, low price, and excellent performance. Cassette recorders can be divided into single player, recorder, tape recorder, stereo tape recorder and recorder according to their functions.
1. The working principle of the tape recorder
(1) The principle of recording and playback
The recording of the tape recorder And playback is an electro-magnetic conversion process. When recording, the audio electrical signal is amplified and sent to the magnetic head coil, and an alternating magnetic flux is generated in the magnetic head iron core on the spot, and a magnetic lift that changes with the audio frequency is formed at the working gap of the magnetic head. When the gap occurs, the magnetic field lines pass through the magnetic layer on the tape, magnetizing it, thus leaving residual magnetism, and as the tape moves at a constant speed, it leaves on the tape a continuity of polarity and strength that varies with the audio signal. Remanence track (as shown in Figure 2-2-6(a))
The acoustic signal is recorded in the form of remanence. During playback, when the tape on which the track is recorded passes through the working gap of the magnetic head at the same speed as during recording, since the magnetic permeability of the magnetic head iron core is much higher than that of air, the magnetic field lines of the residual magnetic field on the tape will pass through the magnetic head iron core. form a closed magnetic circuit. Because the remanence and direction of the magnetic tape on the tape change with the recorded sound signal, the magnetic flux in the magnetic head core also changes accordingly, so that the induced electromotive force ( ) corresponding to the change of the magnetic flux is generated in the coil.
(2) Principle of Bias Magnetic Recording
After the ferromagnetic material is magnetized, even if the external magnetic field is removed, the ferromagnetic material will The magnetic Br still retains a certain r, we call Br as remanence. The greater the applied magnetic field strength H, the greater the remanence Br, until the ferromagnetic substance reaches saturation, draw the relationship curve between Br and H, which is the remanence curve of the ferromagnetic substance. Only the middle section of the remanence curve is a straight line. During recording, if the audio signal is directly fed into the magnetic head, the non-linear segment at the beginning of the residual magnetization curve will produce severe nonlinear distortion of the residual signal (as shown in Figure 2-2-7).
In order to overcome this nonlinear distortion, the DC bias magnetic recording method is used in some popular recorders, that is, a DC bias magnetic current is added to the recording signal to make the audio signal. The operating point is moved up to the straight line segment of the residual curve, but the DC bias method has a smaller dynamic range and higher noise. In the middle and high-end tape recorders, the AC bias magnetic method is commonly used, that is, a super-audio oscillating current (usually 45~100KHz) and 5~25 times larger than the highest frequency of the audio signal is superimposed on the audio signal ( See Figure 2-2-8),
In this way, the working point of the audio signal is moved to the upper and lower straight lines of the remanence curve. The advantages of small noise, large dynamic range and good fidelity.
(3) The principle of erasing
The erasing is to degauss the tape and remove the residual magnetism on the tape. At present, the method of communication erasure is more commonly used. Communication erasure is also known as super audio erasure. The basic structure of the erasing head is the same as that of the recording and reproducing head, but the width of the working gap is about 10 times that of the recording and reproducing head. When erasing, the super-audio oscillator provides super-audio current to the erasing head coil, so that a magnetic field with enough alternating times is generated at the gap of the magnetic head. Repeated action, so that the remanence gradually reduced to zero. The tracks originally recorded on the tape are completely erased.
Another method of erasing is the DC saturation erasing method, in which a DC current is passed through the erasing head coil to generate a magnetic field sufficient to saturate the magnetic material on the tape. When the tape passes through the erasing head gap, the remanence of all copies of the magnetic material on the tape is saturated. In this way, the magnetic flux on the tape is consistent everywhere, and it is impossible to generate an induced electrical signal during playback. This erasing method is often used in combination with the DC bias mode line, which makes the recorder simple and economical.
2. Basic structure of recorder
A recorder generally consists of a magnetic head, a mechanical transmission (called “movement”) and a circuit. The heads of the tape recorder are divided into three types: the recording head, the playback head and the erasing head. The popular tape recorder often combines the recording head and the playback head into one recording and playback head. The mechanical transmission part consists of a driving mechanism, a braking mechanism and various functional operating mechanisms. The circuit part is composed of recording and playback amplifiers, super audio oscillators and some special function circuits. The basic composition of the recorder is shown in Figure 2-2-9.
(1) Mechanical transmission mechanism
The function of the mechanical transmission mechanism is to let the magnetic tape pass through the magnetic head at a constant speed, and make the magnetic head with appropriate tension and reverse tension. , The tape is in close contact, and the tape is wound on the supply and take-up reels at the required speed. The capstan is the core of the mechanical transmission, and the tape is pressed on the capstan by the pinch roller (small rubber roller). Consistent line speed operation.
Although the mechanical system does not directly participate in the magneto-electric conversion, it provides time-space conditions for the magneto-electric conversion, so it is the key part on the right side of the recorder, and the quality of the recorder depends to a large extent. in the movement.
(2) Recording and playback frequency equalization circuit
During playback, the induced electromotive force generated in the playback head coil is proportional to the rate of change of the magnetic flux, so it is also proportional to the rate of change of the magnetic flux. proportional to the frequency of the recorded signal. In this way, the frequency response of the magneto-electric conversion of the playback sound is a straight line rising at a slope of 6dB per octave (as shown by the dotted line in Fig. 2-2-10(a)).
In the actual recording and playback process, there are many kinds of losses. Such as head eddy current loss, gap loss, tape self-degaussing loss, etc. These losses cause the drop of the high-frequency part of the recording and playback (as shown by the solid line in Fig. 2-2-10(a)). It can be seen that if no equalization measures are added, the final sound playback effect will be very poor.
The method to overcome the uneven frequency response of the recording and playback is to add an equalization network to the recording and playback amplifier circuit to correct the actual output characteristic curve. This correction is called frequency equalization or frequency compensation. According to the different frequency response characteristics of recording and playback, it mainly compensates for the high frequency band during recording, and mainly compensates for the low frequency band during playback, and appropriately compensates for the high frequency. As shown in Figure 2-2-10 (b) and (c). After equalization and amplification, the frequency response characteristics of the playback output are integrated into a flat curve, as shown in Figure 2-2-10(d).
In order to ensure the interchangeability of the tape recorder and the tape program, the international standard playback audio characteristic curve is stipulated, and all manufacturers design the recording equalization circuit accordingly. In this way, no matter which program is recorded, it can also be played ideally on any other recorder. The equalization network designed for tapes with different magnetic materials is also different, so pay attention to the correct use of the equalizer (tape select) switch set on the recorder.
(3) magnetic tape
The magnetic tape is the main storage body of the recording signal, which is composed of two parts: the tape base and the magnetic layer. The magnetic layer is a carrier for recording signals. It is a mixture of tape-like substances and adhesives evenly. According to different shapes and structures, it is divided into three types: disc type, cassette type and cassette type. The reel tape has a bandwidth of 6.3m, its magnetic layer is thick, and its performance is good. It is only used for open-reel tape recorders. Cassettes are end-to-end revolving tapes with only one reel, which can be used for language learning, car playback, etc. Cassette tapes are the most widely used. The standard cassettes have the same specifications, but the tapes are long or short, so the recording time is different. The common ones are C-60 (60 minutes), C-120 (120 minutes) and so on. The longer the tape, the thinner the tape base, which is easy to cause twisting during use, and the durability is also poor. Generally, C-60 tapes are used.
According to different magnetic materials, tapes are divided into the following types:
(1) γ-Fe2O3 tapes. γ-Fe2Oz belt, also known as ordinary belt, iron belt, is usually marked with the word Normal, and its magnetic material is ferric oxide with γ-type needle-like structure. The tape marked with “LH” on the cassette is a “low noise” tape, which has poor high frequency characteristics and is not suitable for recording programs with a wide range of rates; the tape marked with “LH” on the cassette is a “low noise and high output” tape. , its magnetic powder particles are finer than “LN” type, and the frequency response is good, which can be used for speech and music recording.
(2) CrO2 tape. CrO2 belt is referred to as chromium belt for short, and its magnetic material is chromium dioxide. The main advantages of chrome tapes are good high frequency characteristics, wide dynamic range, suitable for recording symphony and other music programs with a large dynamic range; the disadvantage is that it has high hardness and wears a lot of magnetic pairs (5~7 times larger than ordinary tapes). , the recorder must have corresponding adjustment and selection devices in the bias and equalization circuits.
(3) Iron-chromium belt. Usually marked with Fe·Cr, it is formed by successively coating γ-Fe2O3 and CrO2 magnetic powder on the tape base. It has the characteristics of γ–Fe2O3 with good low-frequency characteristics and CrO2 with good high-frequency characteristics, and is suitable for recording various high-fidelity music programs with a large dynamic range.
(4) Metal tape. The tape box is marked with “Metal”. The magnetic material of this tape is iron, cobalt, nickel and other metal magnetic powder. It has the characteristics of large output, low distortion, good high frequency retention and not easy to saturate. It is suitable for high-density recording. There is also a cobalt tape with similar properties to the chrome tape, but with less wear to the head.
2. Selection and use of tapes
(1) Choose appropriate tapes according to actual needs and the grade of the tape recorder, so as to make good use of tapes High performance, guaranteed quality, economical and practical, and prolong the life of recorders and tapes.
(2) Check the winding condition of the tape in the cassette before use. If the tape head is loose, it should be wound tightly. To reduce the chance of twisting. For a newly purchased tape, it should be wound one or two times by fast forwarding and fast rewinding before use.
(3) The tapes should be stored upright, do not stack and lay flat to avoid crushing the edges of the tapes. It is strictly forbidden to touch the magnetic layer of the tape with your hands.
(4) Put the tape back in the box after use, and prevent dust from entering, otherwise the dust particles will affect the work of the magnetic head and the tape transport mechanism after being brought into the tape recorder, which will reduce the recording quality and accelerate the magnetic head tape. of wear.
(5) Pay attention to the temperature and temperature of the environment when storing the tape, and avoid high temperature and high temperature. The program tape should be kept away from various magnetic fields to prevent the recorded program from being damaged by magnetization. Program tapes that have not been used for a long time should be rewound regularly to avoid “copying effect” (that is, the mutual magnetization of the upper and lower tapes). Pry off the anti-miswipe sheet to prevent miswiping.
(4) Selection and use of recorder
1. Selection of recorder
The choice of recorder should generally be based on usage, quality and Consider the three aspects of price comprehensively. If it is mainly used for learning foreign languages, listening to Liu’s records, etc., you can choose a cheap and practical monophonic tape recorder; If it is mainly used, a pocket-sized tape recorder should be selected; if it is for family use, portable, desktop and high-fidelity stereo sound combination should be selected according to the family economy and housing conditions; if it is used in hotels, dance halls, and venues, high-power high-fidelity stereo sound should be selected. System.
When selecting, the appearance quality, mechanical performance and electro-acoustic performance of the recorder should be checked.
(1) Appearance quality inspection. In addition to the appearance of the recorder, the appearance should be beautiful and the tone should be harmonious. In addition, it also depends on whether there are dents, cracks and other defects on the surface of the casing, and whether the decorative parts are smooth and bright.
(2) Mechanical performance inspection. The function keys, switches and knobs of the tape recorder are all operated during operation. The hand feel is light, the bounce is flexible, the action is accurate, the tape transport should be stable and smooth, the speed of the tape should be uniform, the winding should be adjusted, the mechanical noise should be small, and there should be no rhythmic sound or “Kada” sound.
(3) Electro-acoustic performance inspection. For the electro-acoustic performance of the tape recorder, the smaller the noise when playing, the better. Press the playback button when the tape is not installed, and turn the volume knob to the minimum position, until the ear noise is close to the tape recorder to hear a slight continuous sound. A steady “rustle” sound is good; put the recorder in fast-forward or fast-reverse state, and turn the volume knob to 1/2 position, no obvious noise should be heard 0.5m~1m away from the machine; distance from the microphone About 0.5m, use the volume of ordinary speech to record, and there should be no obvious distortion during playback; playback of familiar music program tapes should not feel rhythm or pitch distortion; when playback, place the volume button in the middle position. , if you hear enough sound, it means that the output power of the machine has a certain margin. Check the functions on the machine one by one, and they must all operate normally and the effect is obvious.
2. The use of the tape recorder and the Maintenance
There are many types of recorders. Except for the similar basic recording and playback functions, different recorders have many differences in structure and other special functions, and with the continuous development of new technologies and functions Application development, this difference will become larger and larger, so, before using a certain recorder for the first time, you should read the instruction manual in detail to understand its performance and the functions of various buttons, switches, knobs, jacks and indicating devices, and understand its effect on the power supply. , tape, mating parts requirements and connection methods to ensure correct operation.
(1) Use of the recorder
At present, the recorder is very popular, and there is no problem for ordinary people to use it. However, with the wide use of various new technologies such as stereo, Dolby noise reduction system, fast copy and other functions in the recorder, the following points should be paid attention to when using:
①When using the recorder for the first time or the first time Before using a certain type of recorder, you should first read the instruction manual of the recorder, understand its performance, and be familiar with the location, purpose and usage of the buttons, knobs, jacks, etc. of the recorder. Failure to record or damage to the recorder.
②Some recorders can be powered by a variety of power sources. Please check whether the voltage matches before connecting to the power source. In particular, the small cassette recorder should be plugged in when not in use (because the power transformer and the power plug are directly connected, the transformer will heat up and burn out due to long-term power-on).
③When using the recorder in a fixed location or in a place with high ambient humidity, the ground wire of the chassis should be well connected to prevent the recorder from leaking and causing stories. At the same time, it can also reduce the interference of stray magnetic fields and improve the recording quality.
④In order to prevent losses due to operational errors, the anti-mistake wipes on the cassette should be pried off for cassette tapes with important data recorded.
⑤Some recorders are equipped with ALC circuit, which can automatically control the recording level, which is convenient when recording lectures or reports on the spot, and can achieve satisfactory results without adjusting the recording level. But recording music programs, especially those with bands, should be changed to manual control, and the volume knob should be adjusted to the appropriate position.
⑥Although many recorders have the function of double-card fast duplication, the frequency response, dynamic range and other indicators of fast duplication are worse than the original dubbing, so when duplicating a small amount of high-quality music tapes , copied at original speed as .
(2) Maintenance of the recorder
①Cleaning. After the tape recorder works for a period of time, the magnetic powder scraped by the friction between the magnetic head and the tape and the dust on the tape will be attached to the magnetic head, capstan, and pinch roller, affecting normal recording and playback. When cleaning, you can use cotton dipped in anhydrous alcohol or magnetic head cleaner to gently wipe the magnetic head, capstan and pinch roller, etc., or use magnetic head cleaner, but you should read the instructions before use.
②Demagnetize. The magnetic head core of the recorder is a soft magnetic material. After a period of use, it is easy to be magnetic, resulting in the deterioration of the high-frequency characteristics of the recorder and the decrease of the signal ratio. When degaussing, a special cassette-type magnetic head degausser can be used. The general operation is: disconnect the power supply, install the magnetic head degaussing device in the tape compartment of the tape recorder, and press the play key to complete the degaussing of the magnetic head.
③Add oil. The oil filling of the cassette recorder is mainly aimed at the rotating part, which can be used for clock oil or precision instrument oil. When filling oil, first open the case of the recorder, and pour a small amount of oil into the rotating parts such as the motor shaft and the capstan. Do not drip oil on the rubber or plastic parts to prevent deformation and damage to the rubber or plastic parts due to corrosion. .
④Store. The recorder should be stored in a dry place to prevent the magnetic head and the components inside the machine from being damaged by mildew. When using dry batteries for the power supply, if the batteries are not used for a long time, the batteries should be taken out to prevent the electrolyte from leaking out and corroding the contact pieces of the box and the body of the recorder.
