JPS6127806B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a left channel (hereinafter referred to as L channel) and a right channel (hereinafter referred to as R channel).
The present invention relates to a multi-channel stereo level control circuit that reduces noise in the recording system, recording medium, and reproduction system of a multi-channel stereo tape recorder including a multi-channel stereo tape recorder.

As tape recorders become more sophisticated, there has been a demand for reduced noise. However, among the noises, so-called hiss noise generated in the tape and head systems is unavoidable, so circuits have been developed to reduce it as much as possible. When recording, the gain of the input signal is not changed when the level is high, but when the level is low, the gain is increased, and during playback, the opposite operation is performed, so that when the level is high, the gain is not changed, and when the level is low, the gain is not changed. This is intended to reduce noise such as tape hiss noise mixed in the recording and reproducing system by the amount of change in gain by performing reproduction so that the gain is lowered by the amount that the gain is increased.

However, a block diagram of a conventional level control circuit in a multi-channel stereo tape recorder including an L channel and an R channel, for example, an L and R2 channel stereo tape recorder, has the configuration shown in FIG.

In Figure 1, the input signal of the L channel is
The level is compressed by the Lch level compression gain control circuit 1 and the Lch level compression control signal detection circuit 2, and the Lch
The information is recorded on a magnetic tape through a recording amplifier circuit 3. The R channel input signal is input to the Rch level compression gain control circuit 4 independently from the L channel signal.
Then, the level is compressed by the Rch level compression control signal detection circuit 5, and the signal is recorded on a magnetic tape through the Rch recording amplification circuit 6. Next, the L channel signal reproduced by the reproduction head is amplified by the Lch reproduction amplification circuit 7, and the Lch level expansion gain control circuit 8 and
The signal is restored and expanded by the Lch level expansion control signal detection circuit 9 and output. In addition, the reproduced R channel signal is amplified by the Rch reproduction amplification circuit 10, restored and expanded by the Rch level expansion gain control circuit 11 and the Rch level expansion control signal detection circuit 12 independently of the L channel signal, and then output. Ru.

Note that the Lch level compression control signal detection circuit 2, the Rch level compression control signal detection circuit 5, the Lch level expansion control signal detection circuit 9, and the Rch level expansion control signal detection circuit 12 each include an amplifier and a rectifier diode. The circuit consists of a resistor and a capacitor in the subsequent stage.

In this way, a tape recorder using a conventional level control circuit compresses the level of the L channel and R channel independently for recording, and expands the level after playback to reduce noise in the magnetic tape and recording/playback system. There is.

Generally, in two-channel stereo, the signal level of the L channel and the signal level of the R channel do not match. Therefore, when the L channel and the R channel are level-compressed independently, the amount of compression differs for each channel.

As a result, when a level compressed (encoder) signal is played back without using a level expansion (decoder), the L channel and R channel music signals may differ due to the difference in the amount of level compression for the L channel and R channel. There is a level difference,
This has the disadvantage that the localization of the reproduced music signal becomes unbalanced.

In addition, when playing back a level compressed (encoder) signal using a level expansion (decoder), the amount of expansion of the decompression system corresponding to the amount of compression differs for each channel, so the recording and playback of magnetic tape and tape recorders The level of system noise differs between the L channel and the R channel in the output of the restoration/expansion system. In this way, in a two-channel stereo tape recorder using a conventional level control circuit, the noise generated in the magnetic tape and recording/playback system causes a level difference between channels in the restored and expanded output depending on the input signal. Left and right 2
When reproduced by two speakers, this noise is not necessarily localized in the center but moves from side to side, resulting in a noticeable audible discomfort.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and when a level expansion (decoder) is used for a level-compressed signal, the noise of the recording/playback system such as the recording medium is eliminated, and even in the restored and expanded output, there is a level difference between channels. To provide a multi-channel stereo level control circuit that localizes to the center when reproduced by two left and right speakers without causing any noise.

Therefore, the multi-channel stereo level control circuit of the present invention rectifies the input signal for each channel and controls the rectified signal of the channel with a large rectified voltage in common to the multi-channels, without making the control signal detection circuit independent for each channel. By extracting the signal as a signal and using that control signal to control the gain of an independent gain control circuit that receives the input signal of each channel, we have eliminated the difference in level compression and level expansion between each channel. be.

FIG. 2 shows a specific embodiment according to the present invention. In Figure 2, from the Lch and Rch input signals,
Control signals are controlled independently by a level compression control signal extraction circuit 13 and a level compression control signal extraction circuit 14, which have the same configuration as the Lch level compression control signal detection circuit 2 and the Rch level compression control signal detection circuit 5 in FIG. It is extracted as a signal, compared and selected by the level compression comparison and selection circuit 17, and is selected by the Lch level compression gain control circuit 1 and the larger control signal.
The Rch level compression gain control circuit 4 is simultaneously gain controlled to compress the level, and the Lch recording amplification circuit 3 and
The signal is recorded on the magnetic tape through the Rch recording amplification circuit 6.

Further, the signal reproduced by the reproduction head is amplified by the Lch reproduction amplification circuit 7 and the Rch reproduction amplification circuit 10, and is then amplified by the Lch level expansion control signal detection circuit 9 and the Rch level expansion control signal detection circuit 1 shown in FIG.
The control signal extraction circuit 15 for level expansion and the control signal extraction circuit 16 for level expansion, which have the same configuration as 2, independently extract the control signals, and compare and select them in the comparison and selection circuit 18 for level expansion, and select the control signal based on the larger control signal. Then, the Lch level expansion gain control circuit 8 and the Rch level expansion gain control circuit 11 are simultaneously gain controlled to restore and expand.

FIG. 3 shows a specific circuit example of the comparison and selection circuits 17 and 18 shown in FIG. 37
Or 38 is cut in the opposite direction. Furthermore, when the polarity of the control signal is negative, the diodes 37 and 38
is in the opposite direction.

Note that if the circuit configuration of FIG. 3 is used as the comparison selection circuit 17 of FIG. 2, the rectifier diodes and It is also possible to omit the resistor and capacitor at the subsequent stage. Similarly, if the circuit configuration shown in FIG. 3 is used as the comparison selection circuit 18 shown in FIG. It is also possible to omit the resistor and capacitor at the subsequent stage.

As described in detail above, in conventional multi-channel level control circuits, independent control signals are generated for each channel to perform level compression and level expansion.As a result, the amount of compression and expansion differs depending on the channel. If a compressed (encoder) signal is played back without using a level expansion (decoder), the balance of the localization of the instrument will be thrown off. In the case of playback, the noise in the transmission system has a different level in the level-expanded output, which has the disadvantage that the localization of the noise changes. However, the level control circuit for multi-channel stereo according to the present invention has the disadvantage that the control signal detection circuit is Instead of making each channel independent, the input signal is rectified for each channel, and the rectified signal of the channel with a large rectified voltage is extracted as a common control signal for multiple channels, and the control signal is used to obtain an independent gain using the input signal of each channel as input. By controlling the gain of each control circuit, the difference in level compression amount and level expansion amount between channels can be eliminated, and as a result, the above drawback can be eliminated.

Further, if the level compression characteristics and the level expansion characteristics do not match, the input/output characteristics will not be linear, but this will not cause the localization and balance of the multi-channel to be disturbed by the level.

In addition, in the present invention, the input signal for each channel is rectified and the rectified signal of the channel with a large rectified voltage is used as a common control signal for multiple channels as a control signal, but here, the input signal for each channel is Compared to the case of adding and then rectifying and using the rectified signal, we will discuss the peculiar effects of this in the fourth section.
Explain using diagrams.

FIG. 4 shows the observation of the signal waveform of the transmission system using an actual recording/reproducing device. FIG. 4 shows signal waveforms when a 5 kHz sine wave signal is input to the left channel and a 15 kHz sine wave signal is input to the right channel as recording signals. In Figure 4, A is
B is the Lch recording signal waveform, B is the Rch recording signal waveform, and C is the sum signal waveform of A and B. Further, D shows the Lch playback signal waveform after passing through the tape transmission system, and E also shows the Rch playback signal waveform after passing through the tape transmission system.
In the tape transmission system, there is a phase difference or delay time difference between Lch and Rch, and therefore a phase difference or delay time difference occurs between D and E, and the sum signal waveform F becomes as shown in FIG.

As is clear from this waveform, when the envelope of the addition signal is used as a common control signal for Lch and Rch, the recording-side addition signal waveform of C and the reproduction-side addition signal waveform of F become waveforms with completely different amplitudes. Put it away. Therefore, in this case, the amount of compression and expansion will be different, making it impossible to faithfully control the level of the stereo signal.

On the other hand, as is clear from the observed waveform,
The amplitude of the recording side signal waveform and the reproduction side signal waveform in the Lch system is the same, and the amplitude of the recording side signal waveform and the reproduction side signal waveform in the Rch system is the same, so the input signal is rectified for each channel. By selecting the larger rectified voltage and using it as a common control signal, there is no effect of the phase difference or delay time difference between Lch and Rch of the tape transmission system, and it corresponds to the control signal obtained on the recording side. This control signal can also be obtained on the playback side, and the amount of compression and expansion can be made the same between the encoder and decoder, making it possible to realize faithful level control of the stereo signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional multi-channel stereo level control circuit, FIG. 2 is a block diagram showing an embodiment of a multi-channel stereo level control circuit according to the present invention, and FIG. 3 is a comparison selection of FIG. 2. A specific circuit diagram of the circuit, FIG. 4, is a waveform diagram of each part for explaining the effects of the present invention. Explanation of symbols, 1... Gain control circuit for Lch level compression, 2... Control signal detection circuit for Lch level compression, 3... Lch recording amplification circuit, 4... Gain control circuit for Rch level compression, 5... Rch Level compression control signal detection circuit, 6...Rch recording amplification circuit, 7...
...Lch regenerative amplification circuit, 8...Lch level extension gain control circuit, 9...Lch level extension control signal detection circuit, 10...Rch regeneration amplification circuit, 11...
Gain control circuit for Rch level expansion, 12... Control signal detection circuit for Rch level expansion, 13... Control signal extraction circuit for level compression, 14... Control signal extraction circuit for level compression, 15... Control signal for level expansion Extraction circuit, 16... Control signal extraction circuit for level expansion, 17... Comparison selection circuit for level compression, 18...
... Comparison selection circuit for level expansion.

Claims (1)

[Claims] 1. During recording level compression, a multi-channel stereo input signal including a left channel and a right channel is rectified for each channel, and the rectified signal of the channel with a large rectified voltage is extracted as a control signal common to the multi-channels. , with the control signal, an independent gain control circuit that receives the input signal of each channel as input,
A level control circuit for multi-channel stereo, which performs gain control and level compression for each, and records each output signal on a recording medium. 2. When compressing the level of recording, the multi-channel stereo input signal including the left channel and right channel is rectified for each channel, the rectified signal of the channel with a large rectified voltage is extracted as a control signal common to the multi-channels, and with that control signal, An independent gain control circuit that receives the input signal of each channel as input,
Each output signal is controlled in gain and level compressed, and each output signal is made into a level control circuit for multi-channel stereo that plays back the recording medium recorded on the recording medium, and when the level of playback is expanded, multi-channel stereo including the left channel and right channel is generated. The reproduced signal for each channel is rectified for each channel, and the rectified signal of the channel with a high rectified voltage is extracted as a common control signal for multiple channels, and the control signal is used to generate an independent gain using the level-compressed input signal of each channel as input. A level control circuit for multi-channel stereo, characterized in that the input signal for multi-channel stereo is restored by controlling the gain of each control circuit to expand the level.