Characteristics of magnetic tapes. Magnetic tapes
Magnetic tape is what recording is made on and what tape recorders use to reproduce this recording. Happens different widths, thickness and types.
Reel-to-reel tape recorders use tape ranging from 1/4 inch (6.3 mm) to 2 inches (50.8 mm) (it may be narrower or wider).
If the tape has deviations from the width caused by poor workmanship, then:
1. If it is narrower, this may affect the unevenness of the recorded tracks and the penetration of channels.
2. If it is wider, its behavior in the tape drive mechanism is not predictable. Uneven pressure on the heads, the edges of the tape may sharpen the guide posts, and the recording may not be played back as it was made. And in general, such a tape can simply get stuck in the tape drive.
First of all, the tape must record the widest possible range of frequencies. The higher the “transmissibility” of frequencies (especially at low speeds), the better.
Each tape “adds” its own noise to the recording; the less there is, the better.
The uniformity of watering the magnetic layer affects the stability of the signal. Uneven watering can cause dips in the level of the recorded signal.
If the tape is deformed, this may cause it to adhere unevenly to the heads. Which in turn can also lead to signal instability. The presence of deformation can be determined visually. Unwind a little tape from the beginning of the roll (at the beginning the tape may be deformed due to inaccurate threading), then make sure that about 30 cm of the tape hangs freely, without tension. Now look at the tape from its “edge”. If it is not deformed, then outwardly it will be perfectly smooth, like a string. If there is still deformation, then outwardly it will appear corrugated.
The magnetic layer must have good signal “return”. On a configured tape recorder, the output can be checked as follows: you need to set the tape recorder to the mode of receiving an incoming signal and apply a uniform 0db signal of some medium frequency to it (for example, from a generator). Adjust the input signal level controls so that the indicators are in the “0” position, then record on the tape, and then rewind and see what the tape recorded in playback mode (if the tape recorder has a through channel, you can track the recorded signal during recording). If the tape has a good “return”, then in playback mode the recorded signal should be at level “0”. If the recorded signal is lower, then the tape underestimates it. However, during recording, this can be compensated for by feeding a stronger signal to the tape, but this in turn can lead to increased noise and distortion of frequencies. If the recorded level suddenly turns out to be above “0”, then this is most likely due to the fact that the tape recorder is not set to this type tape, or not configured at all.
A tape can have very high recording quality, but everything can be ruined by the shedding of the magnetic or “protective” layer (oh, tape made in the USSR). If the tape “crumbles”, then during its operation you will certainly find out about it. To the ear, the first signs of shedding of the magnetic layer are the disappearance of high frequencies, and then all other frequencies. Visually, the magnetic layer settles on everything it comes into contact with. These include stands and magnetic heads... This phenomenon is more pronounced in Russian-made tapes, and then in tapes intended for household use. Shedding of the magnetic layer can also occur due to poor storage of the tape.
There are methods that temporarily prevent the “shedding” of the magnetic layer. One way: preheat the oven to 100 degrees, turn off the heat, then place the roll there and leave it for 12 hours. There is an opposite way - wrap the roll in a damp cloth and place it in the freezer for several hours, then let the roll dry and rest in room conditions. Experiment at your own discretion (for Russian-made tapes, these experiments are most likely useless).
Household tapes can also creak (whistle) (remember Tasma). One of the possible origins of this squeak is that the magnetic layer settles on the elements of the CVL along with what was “glued” to the lavsan and “rattling” of the tape begins to occur. The thinner the lavsan base of the “whistling” tape, the more likely it is to creak. In some cases, “wetting” the roll temporarily helps. The roll is placed in a medium with high humidity and after some time you can try to play it back (after rewinding it). You can also eliminate the “creaking” by wiping the tape in the “rewind” mode isopropyl alcohol. However, it is difficult to say how long it will take to “eliminate” the “creaking” in this case.
The thicker the tape, the more it rubs the head due to its roughness. Of course, the wear of the heads is also affected by the composition and “smoothness” of the magnetic layer.
There are standards by which film thickness is classified, but these standards are not strict. For example, if you compare the diameters of ORWO 106 and Svema PO 4615 rolls, there will be a slight difference, however, it is believed that they have the same thickness standard. The thickness of the tape is measured in microns (or micrometers (µm). 1m = 1000000µm).
Basic thickness standards:
1) 55 microns. (normal). Thickness of the earliest types of acetane-based tapes (professional and household). The acetane base is very fragile and capricious. It can be “glued” together with basic vinegar. Its most common types produced in the USSR are type 2 and type 6. Its operation has shown that such a tape loves to tear (but here we still need to make allowances for the quality of tape drives of those times), and is very sensitive to deviations in conditions environment(moisture, temperature).
Subsequently, the tape is 55 microns thick. was only professional, already on a lavsan base, but with an additional protective layer. The so-called “protective layer” is usually located on the opposite side, relative to the magnetic layer (it rarely happened that it was between the lavsan and the magnetic layer. One of such tapes is OR WO 103). “ Protective layer” promotes more even winding of the tape (which allows it to be stored on AEG and NAB cores), reduces the magnetic influence of the layers on each other on the roll. It may also reduce the effect of static on the magnetic layer and prevent deformation of the lavsan base.
Examples of 55µm types: RMG SM468, Basf LGR 35P; LGR 50, Agfa PEM 468, Ampex 456, OR WO 104; 106, Svema PO 46 15; NGO 46 20.
For reference: on reel No. 18 at a speed of 19.05 cm/sec, one side sounds for approximately 30 - 32 minutes (350 - 380 m.).
2) 37 - 35 microns. Thickness of the most common household types. The very first types of film, based on lavsan, were of this thickness.
Examples of types 37 - 35 µm: RMG LPR35, Maxel 35-90, Agfa PE 39, OR WO 114, Svema A 4411-6b; B-3716, Slavich B-3719, Tasma B-3711.
For reference: on reel No. 18 at a speed of 19.05 cm/sec, one side sounds for approximately 45 - 48 minutes (520 - 550 m.).
3) 27 microns. (double play). This thickness is mainly applicable to household types of film. Due to the fact that it is quite thin, the lavsan base is more susceptible to deformation. Tape drives that are not adjusted and not adjusted (not tuned) to this thickness can ruin it. Accordingly, the magnetic layer is more limited in the number of overwrites.
Examples of 27 µm types: RMG PM975, OR WO 123, For reference: on reel No. 18 at a speed of 19.05 cm/sec, one side sounds for approximately 60 - 65 minutes (700 - 750 m.).
4) 18 microns. (triple play). A rare thickness used on reel-to-reel tape recorders. Manufacturers of magnetic tape, if they produced film of this thickness, did so in very late batches. Exist different opinions about its quality. Very good feedback about a tape of this thickness from Uher.
Example types: RMG VM953,
For reference: on reel No. 18 at a speed of 19.05 cm/sec, one side sounds for approximately 90 - 100 minutes (1000 - 1100 m.).
For additions to this topic, write to: [email protected]
For magnetic sound recording and video recording, ferromagnetic tape is used as a carrier, consisting of a base on which a layer is applied ferromagnetic substances (working layer). The tape is used as a base cellulose diacetyl, triacetylcellulose, lavsan The best material for the base is lavsan (polyethylene terephthalate). To make the working layer of magnetic tapes, gamma iron oxide, cobalt ferrite, chromium dioxide, etc. are used. Gamma iron oxide is most widely used in modern tapes. Currently used powder gamma oxide iron with needle-shaped particles and sizes of 0.1-0.5 microns. The volume concentration of magnetic powder in the working layer for different tapes is 30-45%.
Released for recording a large number of types of magnetic tapes. There is no generally accepted designation for tapes yet, and manufacturers designate them differently. In the USSR, the type of tape was previously designated by the development serial number (for example, type 2, type 6, type 10). According to GOST 17204-71 “Magnetic tapes. Type designation system" since 1972, a new designation system has been introduced. According to this system, types of tapes are designated by a combination of five elements.
First element - alphabetic, indicating the purpose of the tape: A - sound recording; T - video recording; B - computer technology;. And - an accurate recording.
Second element - digital (from 0 to 9), indicating the base material: 2 - cellulose diacetyl(DAC); 3 - triacetylcellulose; 4 - polyethylene terephthalate.
Third element - digital (from 1 to 9), indicating the thickness of the tape: 2-18 microns, 3-27 microns; 4-37 µm; 6-55 microns; 9 - over 100 microns.
Fourth the element is digital (from 01 to 99), indicating the number of the technological development.
Fifth element - the numerical value of the nominal width of the tape in millimeters.
After the fifth element, an additional letter index is used: P - for perforated tapes; R - for tapes used in radio broadcasting; B - for tapes for household tape recorders.
According to the recommendation of the International Electrotechnical Commission (IEC) of 1959 according to GOST 8303-76 “Magnetic tapes. Basic dimensions”, the width of the tapes is taken to be 6.25 ± 0.05 mm. IN Lately They produce tapes with a width of 3.81 mm, which are used in cassette recorders. Tape thickness according to GOST 8303-76 55 +0 -5, 37 +0 -5, 27 +0 -2 and 18 +0 -2 microns.
Magnetic tapes are evaluated according to the following indicators: physical and mechanical, which determine the properties of the tapes under mechanical and climatic influences; magnetic, which determines the properties in a magnetic field; operational, which characterizes the sensitivity of the magnetic tape to influences during recording and signal distortion during recording and playback.
The physical and mechanical properties of the tapes include the following:
the load corresponding to the yield strength, it characterizes the strength of the tape under static loading;
relative elongation under load, i.e. change in the length of the tape at a given static load;
impact work, i.e. the strength of the tape under dynamic loading;
permanent elongation after impact loading characterizes irreversible changes in the length of the tape after dynamic loading;
abrasiveness, i.e., the degree of wear by the tape of magnetic heads and other stationary parts of the tape transport mechanism with which the tape comes into contact during movement;
sabre- deformation of the tape along its length (caused mainly by pulling out the edge of the tape during cutting); this leads to poor contact between the tape and magnetic heads and distortions of the tape relative to the magnetic heads.
In table 16 shows the physical and mechanical characteristics of various tapes.
The magnetic properties of the tapes depend on the magnetic properties of the initial powder, the volumetric concentration of the powder in the working layer and the degree of orientation of the powder in it and are characterized by coercive force (N s), residual saturation magnetic flux, residual saturation magnetization (I r) or maximum residual induction (IN r )
and relative initial magnetic permeability ( μ ). The main indicators of the magnetic properties of various tapes are given in table. 17.
Performance indicators include electroacoustic, i.e. sensitivity, frequency response, nonlinear distortion, tape noise, copy effect level, optimal magnetization level.In practice, tape performance is determined by comparing a specially selected sample recording medium with a test medium.
The sensitivity of the tape characterizes the ratio of the residual magnetic flux to the low-frequency field of the recording head. Relative sensitivity - ratio (dB) of residual magnetic field when recording a signal with a frequency of 400 Hz to the residual stream on a standard tape in the same recording mode. The higher the tape sensitivity, the lower the recording amplifier gain should be.
Frequency response - the difference (dB) between the output of the standard and test tapes at a frequency of 10 kHz at a given recording speed. The frequency response of the tape depends on its magnetic properties, the thickness of the working layer, the uniformity of particles, the quality of the surface of the working layer and the magnetization mode.
Nonlinear distortions are assessed using the third harmonic. The third harmonic coefficient is equal to the ratio of the third harmonic voltage to the first harmonic voltage of a signal with a frequency of 400 Hz at the output of the playback amplifier. This is an absolute characteristic that determines the nonlinear distortion of the end-to-end path, including the recording amplifier, magnetic tape and playback amplifier.
The relative level of modulation noise (tape noise) is equal to the ratio (dB) of the noise voltage of the tape magnetized with direct current to the maximum value of the signal voltage, measured at the output of the playback amplifier.
The copy effect level is determined at a recording signal frequency of 400 Hz and a recording storage time of 24 hours. It is equal to the ratio (dB) of the largest copy signal to the maximum recording signal.
Optimal magnetization is the magnetization at which the sensitivity of the magnetic tape is maximum. To experimentally determine the level of optimal magnetization, the magnetization characteristic is taken - the dependence of the tape output on the high-frequency magnetization current at DC records. The coordinate of the vertex of the resulting curve determines the level of optimal magnetization. In practice, the relative value of the level of optimal bias is measured, equal to the ratio, expressed in decibels, of the level of optimal bias of the tested tape to the optimal bias of the standard tape.
Electroacoustic performance depends on the thickness of the working layer and the volumetric concentration of the powder. With an increase in the thickness of the working layer of the tape, all other things being equal, the sensitivity increases, nonlinear distortions and noise of the magnetized tape decrease, the frequency response deteriorates and the level of copy effect increases.
With an increase in the volumetric concentration of powder in the working layer, all other things being equal, sensitivity and frequency response improve, nonlinear distortions and noise of the magnetized tape decrease, and the level of copy effect increases. The level of optimal magnetization decreases with increasing powder concentration, and increases with increasing thickness of the working layer. They strive to increase the volume concentration of the powder as much as possible and reduce the working layer of the tape.
Electroacoustic characteristics of magnetic tapes are given in table. 18. The values of the high-frequency bias current (HFB), relative sensitivity, and frequency characteristics of tapes manufactured in the USSR are given relative to a standard tape of type 2. Recently, a new standard tape A4403-6 with a thickness of 37 microns has been released.
The best magnetic tapes for tape recorders are the following:
for studio tape recorders at 38.1 cm/s speed and standard recording level PER 525 (stereo), SPR 50 LH, LGR 30 P;
for studio tape recorders at increased recording levels PER 555 and LR 56 P;
for studio tape recorders at a speed of 19.05 cm/s LPR 35 LH;
for reel-to-reel household tape recorders PES 35 LH, SD;
for household cassette recorders UD 35, HE 35.
Tape, magnetic tape, ferromagnetic tape, is a magnetic recording medium used in tape recorders and. Belongs to the group.
Tape
Magnetic tapes were divided into single-layer - solid, in which particles of magnetic material are distributed in a film-forming material over the entire thickness of the tape, and two-layer, non-magnetic base - cellulose ester or plastic film, paper, etc. - and a ferrolayer of magnetic powder applied to it, sprayed in film-forming material.
In 1958, the industry produced two-layer tapes according to GOST 8303-57: type I, type IB and type II, intended for household and special (professional) tape recorders.
Type I tape was intended for use in magnetic sound recording devices professional type(in radio broadcasting, cinematography, etc.) at a pulling speed of 76.2 cm/sec. The tape consists of a non-flammable cellulose acetate base and a ferromagnetic layer applied to one of its sides. Tape dimensions: width 6.35 mm, total thickness 50-60 µ, magnetic layer thickness 10-20 µ. Type I tape was produced wound on cores (bosses), the length per roll was 1000+50 m. Each roll was packed in a cardboard box that had a special holder for the core.
Type IB tape was intended for use in household magnetic sound recording devices (tape recorders and tape recorders) at speeds of 76.2 and 38.1 cm/sec. In all respects, except for electroacoustic ones, type IB fully corresponded to tape type I. The total thickness of type IB tape is 50-60 µ. It was produced in rolls of 1000±50 m, wound on a core, or on cassettes of 100, 180, 350 and 500+20 m.
Type II tape intended for use in professional and household sound recording devices (MEZ-15, Dnepr, Yauza tape recorders, MP-2 set-top boxes, etc.) at a transfer speed of 38.1; 19.05 and 9.5 cm/sec. The tape had a cellulose acetate base and a ferrocobalt magnetic layer (a mixture of ferrite and cobalt). The thickness of the tape base is 40–45 µ, the thickness of the magnetic layer is 15–20 µ. To improve the frequency response, Type II tape was ground on the magnetic layer side. This layer had a shiny surface, in contrast to the matte magnetic layer of Type I and Type IB tapes. Compared to Type I and Type IB tape, Type II tape was more sensitive; the magnitude of its return is approximately twice as high. Type II tape was produced in rolls of 1000 m on cores and on standard cassettes corresponding to GOST 7704-55.
Schematic section of a two-layer tape
Replacing a type II tape at low pulling speeds with a type 1 tape narrowed the frequency range and greatly reduced the playback volume, for example, at a tape pulling speed of 19.05 cm/sec, such a replacement led to a narrowing of the frequency range to 6000-7000 Hz and a decrease in volume by almost half (with the same nonlinear distortions), replacing type II tape with type IB, the frequency range narrowed to 4000-4500 Hz.
Application of Type II tape on higher speeds, for example, 76.2 cm/sec, is impractical, because this increases the noise level and worsens the erasure of old recordings.
Characteristics of tapes
Type I and type IB tapes were produced in rolls of 1000+50 m on standard 100 mm metal cores and on cassettes.
Standard tape core
Type II tapes were produced in rolls of 1000+50 m and 500+20 m on cores, as well as on standard cassettes.
The cassettes were made of polystyrene, duralumin, or a combination (plastic sleeve, duralumin cheeks). The cassette was supposed to secure the inner end of the tape roll. The nominal capacity of cassettes and the approximate duration of their playback at a tape speed of 19.05 cm/sec are shown in the table below.
Characteristics of tape cassettes (according to GOST 7704-55)
If broken, the tape could be glued together. To do this, the ends of the torn tape were cut off, a drop of glue was applied to one of them from the side of the magnetic layer, after which the ends were overlapped with an overlap equal to the width of the tape (0.5-1.0 cm). When gluing, the ends of the torn tape should not have lateral displacement or skew. The manufacturers recommended the following glue recipe for gluing tape: acetic acid 23.5 cm³, acetone 63.5 cm³, butyl acetate 13.0 cm³. The tape could also be glued with acetone, vinegar essence or universal glue BF-2.
The marking is applied on the smooth (back) side of the manitophone tape (from the base side) along its entire length and included: the name or trademark of the manufacturer, type of tape, year of manufacture and irrigation number.
Standard tape cassette
Signs of defective and poor quality of a tape were cracked or broken cassettes and bushings, bent metal cassettes and cores, breaks in the tape. The end of the tape, after winding it onto the cassette, was glued and sealed with a factory mark; The watering number was indicated next to it. Each roll of tape or cassette, along with instructions for use, was placed in a cardboard folder; the folder was placed in a cardboard box on which the relevant data was indicated.
Tapes should be stored in boxes, in dry, ventilated areas at a temperature of 10-20° and a relative humidity of 50-60%, protecting them from overheating, dampness and exposure to sun rays. Recording tapes should be stored away from large iron masses or strong electromagnetic fields (electromagnets, electric motors, transformers, etc.). When storing records, boxes of tapes were numbered, back side they were designated by the names of the recorded works, performers, recording dates, etc. If necessary, information about the recordings in the music library could be compiled into a general catalog.
Magnetic tape
Magnetic tape reel
Magnetic tape- an information carrier in the form of a flexible tape coated with a thin magnetic layer. Information on magnetic tape is recorded using magnetic recording. Devices for recording sound and video on magnetic tape are called tape recorder and video recorder, respectively. A device for storing computer data on magnetic tape is called a tape drive.
Magnetic tape revolutionized broadcasting and recording. Instead of live broadcasts in television and radio broadcasting, it has become possible to pre-record programs for later playback. The first multi-track tape recorders made it possible to record onto several separate tracks from different sources, and then subsequently combine them into the final recording with the necessary effects applied. Also, the development of computer technology was facilitated by the ability to save data for a long period with the ability to quickly access it.
Sound recording
Magnetic tape was developed in the 1930s in Germany through the cooperation of two large corporations: the chemical concern BASF and the electronics company AEG, with the assistance of the German broadcasting company RRG.
Video recording
VHS video cassette
The world's first video recorder was introduced by Ampex on April 14, 1956. Small company, founded by Russian emigrant Alexander Matveyevich Poniatov in California, was able to make a real breakthrough in video recording technology by inventing cross-line video recording and using a system with rotating heads. They used 2-inch (50.8 mm) wide tape that was wound on reels - the so-called Q (Quadruplex) format. November 30, 1956 - CBS first used Ampex to broadcast a delayed news program. VCRs made a real technological revolution in television centers.
In 1982, Sony released the Betacam system. Part of this system was the video camera, which for the first time combined both a television camera and a recording device in one device. There were no cables between the camera and the VCR, so the video camera gave a lot of freedom to the operator. Betacam uses 1/2" cassette tape and quickly became the standard for television news production and studio video editing.
In 1986, Sony introduced the first digital video recording format, standardized by SMPTE, ushering in the era of digital video recording. The most common consumer digital video recording format was the one introduced in 1995.
Data storage
Cassette QIC-80
Magnetic tape was first used to record computer data in 1951 by the Eckert-Mauchly Computer Corporation on the UNIVAC I computer. The media used was a thin 12.65 mm wide strip of metal consisting of nickel-plated bronze (called Vicalloy). Recording density was 128 characters per inch (198 micrometers/symbol) over eight tracks.
In 1964, the IBM System/360 family adopted the 9-track linear tape standard, which subsequently spread to systems from other manufacturers and was widely used until the 1980s.
Home personal computers of the 1970s and early 1980s (through the mid-1990s) often used a common household tape recorder and compact cassette as the primary external storage device.
In 1989, Hewlett-Packard and Sony developed the DDS data storage format based on the DAT audio format. Digital Data Storage).
In the 1990s, the QIC-40 and QIC-80 standards were popular for personal computer backup systems, using small cassettes with a physical capacity of 40 and 80 MB, respectively.
Notes
Links
- Vladimir Ostrovsky Origins and triumph of magnetic sound recording // "625": magazine. - 1998. - No. 3.
- Valery Samokhin, Natalia Terekhova VHS format turns 30! // "625" : magazine. - 2006. - No. 8.
Wikimedia Foundation.
2010.
The tapes are characterized by three groups of indicators: physical and mechanical, magnetic and working. Main physical and mechanical properties
tapes are: load corresponding to the fluidity of the base material; residual relative elongation after removing the load, relative elongation when exposed to impact load; adhesive strength; sabreability and warping (saberability is determined by the degree of deviation of a piece of tape 1 m long, loosely laid on a flat surface, from a straight line, and warpage is determined by the degree of deformation of the surface of the tape); heat and moisture resistance.
The strength characteristics of magnetic tape are almost entirely determined by its base. The lavsan base, as a rule, provides the strength characteristics required for the tape.
Below are the main physical and mechanical characteristics for a magnetic tape with a width of 3.81 mm on a lavsan base with a thickness of 12 microns:
Magnetic properties of tapes characterized by coercive force (ranges from 20 to 80 kA/m for various types of tapes); residual saturation magnetic flux (5-10 nWb); saturation magnetization (90 - 120 kA/m); residual saturation magnetization (70 - 100 kA/m); relative initial magnetic permeability (1.7 -2.2).
The basic magnetic properties of the tape can be determined from the magnetization curves of the working layer of the tape, which have the form of hysteresis loops. Figure 4.2 shows magnetization curves related to three various compositions working layer of the tape based on Fe 2 O 3, CrO 3 and metal powder. Residual induction is the most important characteristic of the magnetic tape material. The higher this indicator, the greater will be the maximum residual magnetic flux of the tape and, therefore, the greater, all other things being equal, the maximum achievable signal-to-noise ratio.
The magnetization characteristic shows that “metal” tape is capable of providing approximately a twofold gain in the level of the recorded signal compared to chromium dioxide and ferrooxide. “Metal” tapes have minimal distortion and a wide frequency range, but to realize these characteristics, special heads are required that ensure the creation of a significantly higher field strength both when recording a signal and when erasing it.
To the main performance characteristics include: relative sensitivity of the tape and its maximum level; signal-to-noise ratio; signal/echo ratio; frequency range; erasability.
Rice. 4.2. Magnetization curves of tapes with different compositions of the working layer: 1 - Fe 2 O 3 ; 2 - СrO 2; 3 - Me
Relative tape sensitivity - the ratio of the sensitivity of the test tape to the sensitivity of the primary standard tape. The sensitivity of a tape is characterized by the degree of its magnetization, which is defined as the ratio of the residual magnetic flux to the low-frequency field of the head created by the recording field. The higher the sensitivity, the lower the gain the recording amplifier can have.
Primary standard tapes are batches of magnetic tapes with the most optimal properties, produced by leading manufacturers. They are like a standard with which the parameters of the tested tapes are compared when evaluating them. Typical tapes and their characteristics are established by the IEC - the International Electrotechnical Commission.
Uneven sensitivity is characterized by fluctuations in sensitivity along the length of the tape and depends mainly on the uneven thickness of the working layer and the concentration of magnetic powder in it, the deposition of wear products of the tape and dust on the working layer. Within one roll of magnetic tape, sensitivity unevenness should not exceed ± 0.6 dB.
Signal-to-noise ratio is determined by the ratio of the voltage of the maximum reproduced signal to the noise voltage of a tape magnetized by a constant field. Modern tapes have a signal-to-noise ratio of 57 - 62 dB.
Third harmonic coefficient - the ratio of the third harmonic voltage of the reproduced signal with a frequency of 400 Hz to the signal voltage at the output of the reproduction amplifier. The value of this parameter is usually 0.5 -3%.