GB2072926A

GB2072926A - Setting recording level in a tape recorder

Info

Publication number: GB2072926A
Application number: GB8109144A
Authority: GB
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1980-03-24
Filing date: 1981-03-24
Publication date: 1981-10-07
Also published as: DE3110785A1; GB2072926B

Abstract

To obtain an optimum recording level on a tape T a comparator 30 (Fig. 9) compares the level of the signal to be recorded from input 14 with the output of a playback amplifier 24, any level difference being registered on an indicator 34. The recording level is manually increased by a control 16 to a level just below that at which indicator 34 starts to register a level difference in order to obtain an optimum recording level at point A (Fig. 4) on the input/output characteristic of the tape. A comparator control 32 is initially adjusted to give a zero indication on indicator 34 with a switch 20 set to position 20a. A delay line 40 compensates for the spacing between the recording and playback heads 10, 12, and a control 50 is adjusted to compensate for differences in recording sensitivity of different tape types. The inputs to comparator 30 may be supplied via high-pass filter 60, 62 which can be selectively bypassed by means of switches 70, 72. A switch 80 (Fig. 10) may be provided to selectively connect level control 16 to the line input 14 or to an adjustable frequency test oscillator 82. <IMAGE>

Description

SPECIFICATION Tape recorder The present invention relates to a tape recorder and, more particularly, to a tape recorder which is capable of easily detecting the level difference between a recording signal and a reproducing signal of a magnetic recording tape. This type of tape recorder is conveniently used, for example, as a tape recorder in which a precise recording level may be obtained.

With a general conventional tape recorder, merely the recording input signal is detected and indicated as a means for setting it to a standard recording level or for controlling the automatic recording level.

However, with such a detecting means for the recording input signal, the level of the actual recording input signal deviates from a suitable recording level in many cases. The fitness of the setting of the recording level widely influences the recording quality of a desired source, particularly with a cassette tape recorder with which the tape speed is slow. Thus, it is an important factor.

In order to accomplish setting of a precise recording level, many conventional recording level indicators have been proposed such as VU meter and a peak meter (peak indicator).

However, with the conventional indicators of this type, only the input level is indicated. The level of the recording on the tape is not indicated, so that only a recording limited by such reservations may be provided.

Thus, conventional setting of the recording level on the tape has been performed with reference to the input level as a standard. It necessarily follows from this that the level of the actual recording on the tape may not be assessed and has been extremely vague.

With the recent increase in the number of kinds of magnetic recording tapes and the differences in their characteristics, satting of the correct recording level according to the kind of magnetic recording tape used has been impossible to attain.

It is an object of the present invention to provide a tape recorder which is capable of easily detecting the level difference between a recording input and a reproducing output of a magnetic recording tape based on the general tape characteristics.

It is another object of the present invention to provide a tape recorder which is capable of providing a precise recording level.

It is still another object of the present invention to provide a tape recorder which is capable of easily setting and indicating a precise recording level.

It is still another object of the present invention to provide a tape recorder according to which setting and indicating of a recording level may be performed in such a manner that the difference between it and an optimal recording level may be reduced to the minimum.

It is still another object of the present invention to provide a tape recorder according to which the setting and indication of a precise recording level may be easily corrected according to the kind of magnetic recording tape.

It is still another object of the present invention to provide a tape recorder according to which the setting and indication of a precise recording level may be performed in any band without causing saturation, based on the frequency characteristics of magnetic recording tape.

According to a tape recorder of the present invention, a recording input signal is recorded on the magnetic recording tape by a recording system. The one recorded on the magnetic recording tape are reproduced by a reproducing system. A reproducing output signal from this reproducing system and the recording input signal before recording are compared with respect to their levels by a level comparator. A level difference output of this level comparator is processed by processing means.

With such a construction, since the comparison output is based on the level information which is actually recorded on the magnetic recording tape, the level difference between the recording signal and the reproducing signal may be precisely detected.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1 and 2 show level response characteristic curves between the input and output signals, and frequency-level response characteristic curves, indicating the characteristics of a general magnetic recording tape; Fig. 3 shows the circuit connection of the main part of a basic embodiment of a tape recorder of the present invention; Fig. 4 shows an input and output signal response characteristic curve for explaining the mode of operation of the embodiment shown in Fig. 3; Figs. 5(a), 5(b) and 5(c) are views illustrating examples of the indicator used in Fig. 3; and Figs. 6 to 10 show circuit connections of the main parts of further embodiments of the tape recorder of the present invention.

Describing the principles of the present invention first, tape characteristics as shown in Figs. 1 and 2 are known to be obtained during recording and reproduction of magnetic recording tape.

As one of such characteristics, as may be seen from the input and output characteristic curves of 333 Hz and 10 kHz shown by the solid lines of Fig. 1 , within the low range of the input level, the output level increases with an increase in the input level. However, when the input level exceeds a certain level, the output level is saturated. Thus, even when the input level is increased further, the output level decreases. This characteristic is such that the saturation occurs at a lower input level as the frequency becomes higher. Furthermore, as may be seen from the distortion characteristic of the output signal of 333 Hz shown by the broken line of this figure, the distortion abruptly increases as saturation occurs.

As may be seen from the frequency-level response characteristic curves of Fig. 2, the high frequency range drops earlier as the input level becomes higher (i.e., O dB, -10dB, and -20dB).

As may be apparent from these characteristics, when the recording level (manner according to which the input level is supplied) is imprecise, it causes great degradation in the level response characteristics, the distortion characteristics, the frequency characteristics and so on of the reproducing signal, so that correct recording may not be performed.

The present invention is made to provide, instead of a standard level as the recording level by the detection of the input level as in the conventional case, a precise recording level based on information on the level actually recorded on the tape by detecting the difference between the recording input level and the reproducing output level according to the characteristics of the individual tapes used.

Fig. 3 shows a basic embodiment of a tape recorder according to these principles.

Referring to Fig. 3, the present invention is applicable to a 3-head type tape recorder in which a recording head 10, a reproducing head 12, and an erasing head (not shown) are disposed independently of each other. A line input terminal 14 to which is supplied a recording input signal is connected to an input terminal of a recording amplifier 18 through an input level adjuster 16 consisting of a variable resistor or the like. The line input terminal 14 is further connected through the said input level adjuster 16 to a source-side stationary contact 20a of a source and tape change-over switch 20, and an input terminal of a first rectifier 22. An output terminal of the recording amplifier 18 is connected to the recording head 10.

In the source and tape change-over switch 20, a tape-side stationary contact 20b is connected to an output terminal of a reproducing amplifier 24 whose input terminal is connected to the reproducing head 12, and a movable contact 20c is connected to an input terminal of a second rectifier 26 and an input terminal of a line amplifier 28.

Output terminals of the first and second rectifiers 22 and 26 are connected to input terminals 30a and 30b of a two-input level comparator 30. The level comparator 30 has an adjuster 32 for providing a constant output level such as 0 when the two inputs are of the same level. The output terminal of the level comparator 30 is connected to a processing circuit, e.g., an indicator 34, comprising a meter.

The output terminal of the line amplifier 28 is connected to a line output terminal 36.

For recording with a tape recorder of this cnstruction, the source and tape change-over switch 20 is set to the side of the source-side stationary contact 20a. Then, a recording input signal from the line input terminal 14 is recorded on a tape T through the recording system including the input level adjuster 16, the recording amplifier 18, and the recording head 10. At the same time, the adjuster 32 of the level comparator 30 is so adjusted that the indicator 34 as the processing means indicates that both outputs from the first rectifier 22 and the second rectifier 26 are of the same level.

When the source and tape switch 20 is set at the tape-side stationary contact 20b next, the recording input signal recorded on the tape T through the recording amplifier 18 and the recording head 10 is supplied via the second rectifier 26 to one input terminal 30b of the level comparator 30 as a reproducing output signal through the reproducing system including the reproducing head 12 and the reproducing amplifier 24. This reproducing output signal is compared with the recording input signal supplied to the other input terminal 30a of the level comparator 30, and the level difference between them is supplied to the indicator 34 to be indicated.

The input level adjuster 16 is adjusted to obtain an optimal recording level. During the process of raising the recording input level with this adjuster, signals of the same level are supplied to both of the respective input terminals 30a and 30b of the level comparator 30, according to the actual characteristics of the tape, up to the level A of the line range of Fig. 4, so that the indicator 34 indicates a constant level difference such as 0.

However, in the range wherein the recording input level is above A, at the level B where the reproducing output is saturated, there is a level difference between the recording input signal and the reproducing output signal supplied to the respective input terminals 30a and 30b of the level comparator 30. Thus, the indicator 34 indicates a level exceeding the constant level described above by this difference.

It is therefore seen that the optimal recording input level may be obtained by setting the indication of the indicator 34 to the level A immediately before exceeding the constant level.

The indicator 34 may be in the form of a meter as shown in Fig. 5(a), or it may be a dot indicator or a peak indicator such as an LED as shown in Figs. 5(b) and Fig. 5(c). Other modifications may also be made within the spirit and scope of the present invention.

The above description has been made assuming a case wherein the optimal recording level is manually set by the operator by adjusting the input level adjuster 16 while supervising the indicator 34. However, the method of utilizing the level comparison results of the recording input signal and the reproducing output signal supplied from the level comparator is not limited to this.

Since the comparison results obtained by comparing the recording input signal and the reproducing output signal are based on the level information actually recorded on the tape, an optimal recording level may be conveniently obtained.

Fig. 6 shows still another embodiment of the present invention which is a modifica#tion of the basic embodiment described above. In this embodiment, an error attributable to a time difference between the recording input signal and the reproducing output signal due to the distance I between the recording head 10 and the reproducing head 12 is eliminated so that a more precise level comparison and detection of the level difference may be attained, and the optimal recording level may be set and displayed.

The construction of the embodiment shown in Fig. 6 is basically the same as the basic embodiment shown in Fig. 3, except that a delay line 40 is inserted in front of the first rectifier 22, that is, in the path of the recording input signal.

However, since the delay line 40 is inserted in the path of the recording input signal, the timings of both signals are matched in the level comparator 30 and the indicator 34, eliminating the time difference between the recording input signal and the reproducing output signal due to the distance between the recording head 10 and the reproducing head 12. Thus, correct level comparison and indication of the level difference may be attained, and indication of the optimal recording level may be attained while reducing the error to the minimum.

The delay time provided to the recording input signal by the delay line 40 is set to be about 50 to 100 msec. This value is based on the case wherein the distance between the recording head and the reproducing head housed within the single solid state of a recent 3-head type cassette tape recorder is 2.5 to 5 mm and the tape speed is 4.75 cm/sec. However, the delay time need not be limited to this but may be determined according to the distance between the two heads and the tape speed.

When a predetermined difference is maintained between the time constants of the smoothing integrating circuits (not shown) provided with the first rectifier 22 and the second rectifier 26 so that the former is larger than the latter, the recording input signal and the reproducing output signal may be made to coincide, and the same effects may be obtained as in the case wherein the delay line 40 is inserted, without actually inserting the delay line 40 in the recording input signal path.

Fig. 7 shows still another embodiment of the present invention which is another advanced modification of the basic embodiment of the present invention. The same reference numerals denote the same parts as in Figs. 3 and 6. This embodiment has been made in consideration of the fact that the tape characteristics greatly differ according to the kind of magnetic recording tape, and the optimal recording level of one tape may not necessarily be the optimal recording level of another. Thus, this embodiment is characterized in that correct recording sensitivity may be easily attained according to the kind of tape used.

The embodiment shown in Fig. 7 is basically the same as the basic embodiment shown in Fig. 3, except that a level adjuster 50 for correcting the recording sensitivity according to the kind of tape used is inserted immediately in front of the recording amplifier 1 8 described hereinabove and the delay line 40 is included immediately in front of the first rectifier 22 for matching the timings so as to eliminate the time lag between the recording input signal and the reproducing output signal.

A case is now considered wherein, after setting the optimal recording level for a certain kind of tape as in the above basic embodiment, the setting is altered for another kind of tape. When it is assumed that the former tape is a normal tape and the latter tape is a metal tape, the saturation point of the latter is significantly higher than that of the former. Thus, without resetting, an indication is made to the effect that there is a difference between the input and output levels, and the level has reached the saturation point.

In the case of this embodiment, before setting the optimal saturation level, a correction may be made by the level adjuster 50 for correcting the recording sensitivity according to the kind of tape so as to make the input and output levels the same. By this recording sensitivity correction, an offset is provided to adjust to the characteristics of the latter tape. By adjusting with the input level adjuster 16, the setting to the optimal recording level of the latter tape may be accomplished.

Setting of the optimal recording level may be performed by similar procedures even when the kinds of the tapes are reverse from the case described above.

In the above embodiment, the level adjuster 50 may operate to vary the gain of the recording amplifier 18. Further variations and modifications may be made within the spirit and scope of the present invention.

The delay line 40, as in the case of Fig. 6, reduces the time difference between the recording input signal and the reproducing output signal caused by the distance between the recording head 10 and the reproducing head 12 for correct comparison of the input and output levels so that a more precise recording level may be attained.

Fig. 8 shows still another embodiment of the present invention which is an advanced modification of the basic embodiment shown in Fig. 3. The same reference numerals denote the same parts as in Figs. 3, 6 and 7. This embodiment has been made in consideration of the fact that level saturation occurs earlier and the level variation is greater with higher frequencies, as may be apparent from the general characteristics of the tapes. Thus, this embodiment is characterized in that the level difference detection is performed with particular attention to high frequency signals so that the optimal recording level may be set in any band without causing saturation.

The embodiment shown in Fig. 8 is basically the same as the basic embodiment shown in Fig. 3, except that high-pass filters 60 and 62 are inserted in front of the first and second rectifiers 22 and 26 and in front of the respective input terminals 30a and 30b of the level comparator 30.

By including the high-pass filters 60 and 62, the high frequency components of the recording input signal and the reproducing output signal alone are extracted at the level comparator 30 for comparison, and the level difference of these is indicated at the indicator 34. Accordingly, setting of the recording level is accomplished with particular attention to the high frequency components which are problematic in tape characteristics, and an optimal recording level may be set in any band without causing saturation.

Fig. 9 shows still another embodiment of the present invention. The same reference numerals denote the same parts as in Figs.3,6.7 and 8. In this embodiment, the high-pass filters 60 and 62 inserted in the embodiment in Fig. 8 may be selectively bypassed with switches 70 and 72.

Thus, according to this embodiment, selection may be made between a setting with particular attention to the high frequency range and an overall setting for the dynamic range according to the characteristics of the signals to be recorded for more convenience to the user.

Fig. 10 shows still another embodiment of the present invention. The same reference numerals denote the same parts as in Fig. 3. The embodiment of Fig. 10 is basically the same as that shown in Fig. 3 except that, instead of inserting the high-pass filters 60 and 62 as in the embodiments shown in Figs. 8 and 9, a testing oscillator 82 is so connected that it may be selectively switched between the line input terminal 14 by a switch 80, and the output frequency of the testing oscillator 82 is switched by a switch 84 at several points, at each of which an optimal recording level may be obtained.

In summary, according to the present invention, a tape recorder may be provided which is capable of providing a precise recording level based on the level actually recorded on the tape, by comparing the recording input level and the reproducing output level considering the general characteristits of the tape. Furthermore, a tape recorder may also be provided which is capable of easily indicaiting and setting an optimal recording level, reducing the error to a minimum and easily correcting the level according to the kind of tape, without causing saturation in any band.

Claims

1. A tape recorder comprising a recording system for recording a recording input signal on a magnetic recording tape, a reproducing system for reproducing a reproducing output signal recorded on the tape by said recording system, a comparator for comparing levels of said reproducing output signal from said reproducing system and said recording input signal, and means for processing a level difference output from said comparator.

2. A tape recorder according to claim 1, wherein said means for processing a level difference output from said comparator comprises an indicator.

3. A tape recorder according to claim 1, wherein said recording system includes a level adjuster for adjusting the input level of said recording input signal.

4. A tape recorder according to claim 1, wherein said recording system and said reproducing system include timing matching means for matching the timings of said recording input signal and said reproducing output signal.

5. A tape recorder according to claim 1, wherein said recording system includes level adjusting means for correcting the recording sensitivity according to the kind of tape.

6. A tape recorder according to claim 1, wherein said recording system and said reproducing system include high-pass filters for independently extracting high frequency components from said recording input signal and said reproducing output signal.

7. A tape recorder, substantially as hereinbefore described with reference to the accompanying drawings.