Automatic adjustment of biasing current for recording sound by three-head type tape-recorder

Claim 3

The method of claim 1 wherein the chronological consecutive alterations of the recording bias current intensity are performed in consecutive stepwise manner.

Claim 4

The method of claim 2 wherein the consecutive stepwise alterations of the recording bias current intensity are performed in a manner of lowering the intensity step after step and the stopping of such stepwise lowering of the recording bias current intensity is caused upon finding that the reproduced output sound level of the higher frequency signal has just become substantially higher than that of the lower frequency signal.

Claim 5

In a three-head type tape-recorder equipped with a recorder head (7) and a reproducer head (9) as well as an eraser head, one separate from and independent of another, so that recording sound by the recorder head (7) on a running magnetic tape (8) and immediately reproducing the recorded sound by the reproducer head (9) immediately downstream of the recorder head (7) in the sense of the tape-running may be made, AN APPARATUS for automatically establishing proper adjustment of biasing current for recording sound, comprising: a pule generator (12) adapted to generate successive pulses during the running of the magnetic tape (8), a counter circuit (14) adapted to consecutively count up number of the pulses, a D/A convertor (15) adapted to receive as input therefor the pulse number digital output and to give as output thereof stepwise voltage with the consecutive stepwise output voltage variations in response to the consecutive counting up of the pulses, a buffer amplifier (16) adapted to amplify the stepwise voltage, a bias generator (6) adapted to receive as input therefor the amplified stepwise voltage and to give as output thereof the recording bias current of the intensity chronologically consecutively altered stepwise responsive to the amplified stepwise input voltage, a mixer circuit (4) adapted to generate composite calibration signal by mixing a lower frequency signal and a higher frequency signal, both of the signals having sound level identical with each other, a parallelly interconnected pair of a high pass filter (17) and a low pass filter (19) adapted to separate, into the component lower and higher frequency signal outputs, the composite calibration signal as reproduced by the reproducer head (9) immediately after being recorded by the recorder head (7) on the running magnetic tape (8), a pair of separate, independent rectifier circuits (18 and 20) adapted to rectify the signal outputs of the filters (17 and 19), respectively, a voltage comparator circuit (22) adapted to receive as input therefor and compare with each other the rectified output voltages of the rectifier circuits (18,20) and to give as output thereof a pulse signal upon finding, as a result of the comparing, that the rectified voltages have become substantially identical with each other or that the rectified voltage difference has just been substantially reversed, namely that the rectified voltage of the output of one filter, initially smaller than that of the other, has just become substantially larger than that of the other, a RS flip-flon circuit (23) with two outputs (F,F) which are inverse to each other with respect to their high and low level states and which are adapted to be switched as triggerd by the pulse output signal of the voltage comparator (22), an AND-gate (13) adapted to pass forward, as input to the counter circuit (14), and to block up, the successive pulses of the generator (12) depending upon the high and low level states, respectively, of one output (F) of the flip-flop circuit (23), a recording-input-signal selection circuit (25) adapted to be switched between two conduction states, namely to sound signal line terminal contact (L) and to calibration terminal contact (C), depending upon the high and low level states, respectively, of the other output (F) of the flip-flop circuit (23), and a starting-pulse-input terminal (24) adapted to receive, at the beginning of the recording, a starting pulse to reset both the counter circuit (14) and the RS flip-flop circuit (23) to their initial states.

Claim 6

In a three-head type tape-recorder equipped with a recorder head (7) and a reproducer head (9) as well as an eraser head, one separate from and independent of another, so that recording sound by the recorder head (7) on a running magnetic tape (8) and immediately reproducing the recorded sound by the reproducer head (9) immediately downstream of the recorder head (7) in the sense of the tape-running may be made, AN APPARATUS for automatically establishing proper adjustment of biasing current for recording sound, comprising: a pule generator (12) adapted to generate successive pulses during the running of the magnetic tape (8), a counter circuit (14) adapted to consecutively count up number of the pulses, a D/A convertor (15) adapted to receive as input therefor the pulse number digital output and to give as output thereof stepwise voltage with the consecutive stepwise output voltage variations in response to the consecutive counting up of the pulses, a buffer amplifier (16) adapted to amplify the stepwise voltage, a bias generator (6) adapted to receive as input therefor the amplified stepwise voltage and to give as output thereof the recording bias current of the intensity chronologically consecutively altered stepwise responsive to the amplified stepwise input voltage, a mixer circuit (4) adapted to generate composite calibration signal by mixing a lower frequency signal and a higher frequency signal, both of the signals having sound level identical with each other, a parallelly interconnected pair of a high pass filter (17) and a low pass filter (19) adapted to separate, into the component lower and higher frequency signal outputs, the composite calibration signal as reproduced by the reproducer head (9) immediately after being recorded by the recorder head (7) on the running magnetic tape (8), a pair of separate, independent rectifier circuits (18 and 20) adapted to rectify the signal outputs of the filters (17 and 19), respectively, a voltage comparator circuit (22) adapted to receive as input therefor and compare with each other the rectified output voltages of the rectifier circuits (18,20) and to give as output thereof a pulse signal upon finding, as a result of the comparing, that the rectified voltages have become substantially identical with each other or that the rectified voltage difference has just been substantially reversed, namely that the rectified voltage of the output of one filter, initially smaller than that of the other, has just become substantially larger than that of the other, a RS flip-flon circuit (23) with two outputs (F,F) which are inverse to each other with respect to their high and low level states and which are adapted to be switched as triggerd by the pulse output signal of the voltage comparator (22), an AND-gate (13) adapted to pass forward, as input to the counter circuit (14), and to block up, the successive pulses of the generator (12) depending upon the high and low level states, respectively, of one output (F) of the flip-flop circuit (23), a recording-input-signal selection circuit (25) adapted to be switched between two conduction states, namely to sound signal line terminal contact (L) and to calibration terminal contact (C), depending upon the high and low level states, respectively, of the other output (F) of the flip-flop circuit (23), and a starting-pulse-input terminal (24) adapted to receive, at the beginning of the recording, a starting pulse to reset both the counter circuit (14) and the RS flip-flop circuit (23) to their initial states.

Claim 7

The apparatus of claim 4 wherein the D/A convertor (15) is adapted to give as the output thereof chronologically consecutively lowering stepwise voltage and the voltage comparator circuit (22) is adapted to give as the output thereof the pulse signal upon finding that the rectified voltage of the output of the high pass filter (17) has just become substantially larger than that of the low pass filter (19).

Claim 8

The apparatus of claim 5 further comprising a DC-shifter circuit (21) in the output line of the rectifier circuit (20) for the low pass filter (19), adapted to give a DC-shifting to the rectified output voltage of the rectifier circuit (20), the DC-shifting being far smaller than the rectified output voltage of the rectifier circuit (20) but larger than possibly foreseeable noise voltage.