JPS6240761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a record board on which a multidimensional sound signal with a richer sense of direction and presence than conventional record boards is recorded.

Conventional 4-channel stereo systems include a discrete type (4-4-4), a matrix type (4-2-4), and a pseudo 4-channel type (2-2-4).
4). Furthermore, one of the recent applicants, J.H. Cooper, has proposed a "universal matrix method" (hereinafter simply referred to as the UM method), which has more advantages than any of these methods. This has advantages such as excellent compatibility between monaural and ordinary two-channel stereo, faithful representation of sound sources, good sound image localization, and freedom in speaker arrangement.

Below, we will give an overview of how this UM method is applied to 4-channel stereo. FIG. 1 is a block diagram of the record cutting system. Four signals SLF, S _RF , S _LB from sound source 1
and S _RB are obtained. These four signals are obtained, for example, from microphones arranged corresponding to the speakers LF, RF, LB, and RB arranged orthogonally (2+2 arrangement) in the listening space surrounding the listener 20 in the record reproduction system shown in FIG. This speaker LF,
Let SLB, S RF , S LB , and S _RB be electrical signals obtained from microphones corresponding to _RF , _LB , and RB.
These four signals are given to the encoder 2, and from the encoder 2, TL, TR,
TT and TQ signals can be obtained. The TL and TR signals are called main channel signals, and the TT and TQ signals are called subchannel signals.

If the respective transmission signals TL, TR, TT, and TQ are expressed as vectors, they will be as shown in FIG. 2.

Main channel signal TL from this encoder 2
and TR are supplied to a mixing circuit 5 via a recording equalizer 4. The characteristics of the recording equalizer 4 are standardized as RIAA recording characteristics, and are curve 3 shown in FIG. One width channel signal TT and
TQ uses an angle modulator 6 to angle-modulate the carrier signal _c . The sub-channel signals TT and TQ obtained by angle-modulating the carrier wave of frequency _c are called modulated sub-channel signals TT' and TQ'. These modulated sub-channel signals TT' and TQ' are fed to the mixing circuit 5
is added to the sub-channel signal at (TL + TT′)
Two transmission signals of (TR+TQ') and (TR+TQ') are formed. These two transmission signals pass through a recording amplifier 7 and are supplied to a 45-45 cutter 8 similar to that used to create conventional stereo records. ') is engraved on the other side, and a signal (TR + TQ') is engraved on the other side.
This embodiment is illustrated in FIG. That is, the main channel signal TL and the modulated sub-channel signal TT' are recorded on one groove wall 9L of the sound groove, and the main channel signal TR and the modulated sub-channel signal TQ' are recorded on the other groove wall 9R. Ru.

A system for reproducing records recorded in this manner is shown in the block diagram of FIG. pick up 2
The reproduced signal from 1 is given to a preamplifier 22. The main channel signals TL and TR taken out from the preamplifier 22 are supplied to a decoder 24 via a reproduction equalizer 23 whose characteristics are opposite to those of the recording equalizer 4. Further, the modulated sub-channel signals TT' and TQ' extracted by the preamplifier 22 via the bandpass filter 25 are demodulated by the angle demodulator 26. Sub-channel signal from angle demodulator 26
TT and TQ are supplied to the decoder 24 along with main channel signals TL and TR, and from the decoder 24 audio signals SLF, S _RF , S _LB and S
A signal similar to _RB can be obtained. and this signal
The SLF, SRF, SLB and SRB are supplied via the amplifier 27 to the corresponding speakers LF, RF, LB and RB in the (2+2) arrangement.

SUMMARY OF THE INVENTION An object of the present invention is to provide a record board that reduces uptalk due to tracing distortion that occurs in a region where the frequency of a sub-channel signal becomes high, and also reduces the influence of beat distortion.

First, let's discuss the problems that occur in the multidimensional audio signal recording and reproducing device described above.

First, there is a problem regarding the limit on the amount of frequency shift. Overmodulation when the carrier is modulated at a low frequency occurs when the peak frequency deviation exceeds the frequency limit established for the modulated subchannel. However, when the carrier wave is modulated with a high frequency signal, the modulated subchannel signal will have frequency components that are more spread out than the peak frequency shift. For example, the maximum frequency deviation such that 5% of the carrier wave energy is outside the 10KHz band on both sides is line 3 in Figure 6.
It has a step-like shape indicated by 0a. This trend is line 3
It can be shown as 0b. On the other hand, when the modulated sub-channel signal passes through the band-pass filter 24 for separating the modulated sub-channel signal in the reproduction system, demodulation distortion occurs. As an example, if the limit at which harmonic distortion of 5% occurs is determined, a step wave-like curve as shown by 31a in FIG. 6 will be obtained. For a symmetrical filter, the harmonic distortion will be of odd orders; for a single sideband filter, the harmonic distortion will be of even orders;
A straight line 31b shows the general trend. The modulation curve of the side channel signal cannot exceed lines 30a and 30b.

A second problem is that when crosstalk exists between modulated sub-channel signals, beat distortion occurs in the demodulated sub-channel signals. Generally, crosstalk occurs when recording and playing back signals on a record. Crosstalk that occurs during recording occurs from the cutter head, cutter needle, etc., and expensive cutter heads and needles are required to eliminate crosstalk. Further, crosstalk that occurs during playback occurs when a pickup picks up a signal from the sound groove of a record, and it is difficult in manufacturing to completely eliminate pickup crosstalk. The process of generating beat distortion due to crosstalk in the carrier frequency band produces nonlinear and complex harmonic distortion and cross-modulation distortion when the relative phase shift is large. In other words, if the groove wall crosstalk is an in-phase component, the distortion will be an odd-order component, and if X is the peak phase shift difference, J _2o
-1(x)/x (n is a positive integer), and if the crosstalk is an orthogonal component, the distortion will be an even-order component, and J
It is proportional to _2o(x)/x (n is a positive integer). Here J _o
(x) is an n-th Betzel function of the first kind. Also, distortion is proportional to the size of crosstalk, and J _3(x)
/x component is maximum when (x=3.6), and J _2(
x)/x component is maximum when (x=2.3), and (x
= 3.8), the J _2(x)/x component and the J _3(x)/x component become equal. The harmonic distortion at this time is that the crosstalk is -
At 20dB, it is approximately 2%. When the modulation index is 3.8 radians, it is the limit for low-order and high-order distortion to occur, and this is the limit level of the modulation index difference.
This half value is shown by line 32 in FIG. When the modulation curve of the sub-channel signal exceeds this line 32, beat distortion increases.

A third problem is crosstalk from the main channel signal to the sub-channel signal that occurs during reproduction. This crosstalk is called uptalk. On the other hand, crosstalk from the sub-channel signal to the main channel signal is called downtalk. Although this downtalk becomes a problem when tracing distortion occurs, it does not become a problem when the modulated sub-channel signal is recorded at a constant speed. On the other hand, uptalk is caused by both tracking angle error and tracing distortion.

Uptalk due to tracking angle error causes the modulated sub-channel signal to undergo phase modulation of (2π/λc am tanφ) when the displacement of the modulated sub-channel signal is smaller than the displacement of the main channel signal. Here, am indicates the displacement of the main channel signal, λc indicates the wavelength of the carrier signal, and φ indicates the tracking error angle. For example, uptalk due to the vertical tracking error angle is mainly caused by the vertical component (difference signal component) of the main channel signal. Now, the main channel signal is RIAA shown in Figure 3.
When recorded with recording characteristics, the limit at which uptalk occurs for a vertical tracking error angle of 5 degrees is shown by line 33.

Further, although unrelated to the influence of the main channel signal, rotational irregularities or flutter cause rumble-like distortion in the demodulated signal. The distortion has the same components as uptalk. The effect on the subchannel by, for example, 0.1% flutter is shown by line 34. Therefore, the modulation curve of the sub-channel signal must be above these lines 33 and 34.

Also, uptalk due to tracing distortion occurs from the main channel signal to the subchannel signal at each of the two groove walls. The sum of these uptalks is shown by line 35. This characteristic 35 applies when the recording speed is 11.5 mm/s and the needle diameter is 5 μ. If the error in the needle tip diameter is within 10%,
As will be described later, the uptalk caused by tracing distortion can be reduced by 20 dB by performing phase modulation in the opposite phase in the record cutting system's re-modulator.

As mentioned above, the things that affect the sub-channel signal are the rumble-like distortion 34 of the demodulated signal caused by uneven rotation in the low range, and the crosstalk between the uptalk 33 and the sub-channel signal due to tracking angle error. Beat distortion by 32
That is. Furthermore, in the middle and high frequencies, uptalk 35 due to tracing distortion and clipping distortion 31b due to frequency band limitation affect the sub-channel signal. Here, the beat distortion 32 caused by crosstalk between the uptalk 33 and 35 caused by the main channel signal and the sub channel signal, and the clipping distortion 31b caused by frequency band limitation are collectively referred to as crossover modulation distortion. Make it.

The present invention is a record board in which uptalk 35 due to tracing distortion occurring particularly in a region where the frequency of the sub-channel signal becomes high is reduced in consideration of the above-mentioned points.

Uptalk due to tracing distortion occurs when a pickup plays a record because the diameter of the tip of the pickup's stylus is finite. Then, the linear velocity S (cm/sec) of the sound groove of the record and the peak velocity amplitude V (cm/sec) of the sound groove of the main channel signal
sec) and the radius r (cm) of the spherical surface of the tip of the reproducing needle, the sub-channel signal undergoes phase modulation, and the amount, expressed by the phase modulation index m, is as follows.

m=rvω/s ² However, in the above formula, ω is the carrier angular frequency (=2π _c )
, and the linear velocity S of the sound groove is the diameter of the sound groove D
(cm) and the number of revolutions per minute is N, then S=πDN/6
0 (cm/sec).

Also, the main channel signal is recorded as shown in Figure 3.
When equalized by the RIAA characteristic and the record diameter is constant, the phase modulation index m increases according to the frequency of the main channel signal.

Based on this consideration, the present invention subtracts the influence of uptalk due to tracing distortion in advance when phase modulating the sub-channel signal in a record cutting system, thereby reducing the amount of tracing distortion during playback. It is a record board that removes the uptalk that occurs.

FIG. 8 shows an embodiment of a record cutting system for producing a record board according to the present invention.

In this embodiment, two sub-channel signals (TT+kTQ) and (TT-kTQ) formed by the matrix circuit 10 are used as sub-channel signals. And this sub-channel signal (TT+
kTQ) and (TT-kTQ) are applied to emphasis circuits 11a and 11b, respectively. The characteristics of the emphasis circuits 11a and 11b are determined so that the modulation curve of the sub-channel signal is as shown by line 36 in the sixth section. This is to eliminate the cross modulation distortion mentioned above.

That is, the sub-channel signal is arranged to be above the lines 32, 33 and 34 in the low frequency region. Further, when moving from the middle range to the high range, the modulation curve 36 is matched to a midpoint between the lines 31b and 35. As a whole, emphasis circuits 11a and 11b are used to realize such a modulation curve 36.
The characteristics of the recording of the main channel signal are shown in Figure 3.
It is said to have similar characteristics to RIAA characteristics, and is said to provide good separation during playback.

Furthermore, the reason why (TT+kTQ) and (TT-kTQ) are used as the sub-channel signals is to reduce the influence of the above-mentioned beat distortion. In other words, the sub-channel signals TT and TQ in the case of the UM system
is shown in Fig. 2, so it corresponds to the relative phase shift of these two sub-channel signals (TT-
The difference vector of TQ) is shown in Figure 7,
In this case, the way the beat distortion appears depends on the position of the sound source. Therefore, if two signals (TT+kTQ) and (TT-kTQ) are selected as sub-channel signals, their relative phase shift will be 2kTQ.
Therefore, the relative phase shift has a uniform distribution depending on the position of the sound source, and its magnitude is also smaller than in the case of (TT-TQ).

Considering the above points, two sub-channel signals are selected so as to increase the in-phase component and decrease the anti-phase component, and the modulation curve thereof is shown as 36.

In Fig. 6, 37 shows the modulation curve for the in-phase component TT between this sub-channel signal (TT+kTQ) and (TT-kTQ) (k=1/3), and 38 shows the modulation curve for their anti-phase component kTQ. (k=1/3).

Now, these sub-channel signals (TT+kTQ) and (TT-kTQ) are supplied to adder circuits 12a and 12b. A compensation main channel signal is supplied to the adder circuits 12a and 12b. The compensation main channel signal is formed as follows. The main channel signals TL and TR that have passed through the recording equalizer 4 are level control circuits 13a and 13b, respectively.
supplied to Level control circuits 13a and 13b
is supplied with a control voltage associated with the operation of the cutter race of the 45-45 cutter 8.

The outputs of the level control circuits 13a and 13b are made equal to the tracing distortion component expressed by the above-mentioned equation (m=rvω/S ² ). The outputs of the level control circuits 13a and 13b are supplied to inversion circuits 14a and 14b, respectively. Inversion circuit 14
The output of a, that is, the main channel signal for compensation is added to the sub-channel signal (TT+kTQ) recorded on the same groove wall of the record in an adder circuit 12a.
On the other hand, the output of the inverting circuit 14b, that is, the main channel signal for compensation, is added to the sub-channel signal (TT-kTQ) recorded on the same groove wall in the adding circuit 12b.

The corrected sub-channel signal (TT+kTQ)′ which reversely corrects the expected tracing distortion in this way
and (TT−kTQ)′ are supplied to the phase modulator 6. The modulated sub-channel signals (TT+kTQ)'' and (TT-kTQ)'' from the phase modulator 6 are sent to the mixing circuit 5.
Two signals [TL+(TT+kTQ)″] are added to the main channel signal at the mixing circuit 5 and obtained from the mixing circuit 5.
and (TR+(TT-kTQ)'') are supplied to the 45-45 cutter 8 via the amplifier 7 and recorded on the left and right groove walls of the sound groove, respectively.

A record reproducing system for reproducing the record of the present invention recorded in accordance with the above-described embodiment includes a reproduction signal extracted from a pickup 21 shown in the block diagram of FIG. 9, which is separated by a band-pass filter 25. The modulated sub-channel signal is provided to the FM demodulator 26. The demodulated output from the FM demodulator 26 is sent to a matrix circuit 28 via emphasis circuits 27a and 27b whose characteristics are opposite to those of the record cutting system emphasis circuits 11a and 11b.
supplied to Sub-channel signals TT and TQ are obtained from the matrix circuit 28, and are supplied to the decoder 24 along with the main channel signals TL and _{TR .} S _RB is obtained,
Each signal is amplified in width and supplied to speakers LF, RF, LB, and RB.

Since the record board of the present invention reversely corrects the sub-channel signal by the amount of expected tracing distortion during record cutting, it is possible to prevent uptalk from occurring during playback.

Note that when forming the main channel signal for compensation, the main channel signal supplied to the level control circuits 13a and 13b must be the same as the one that is finally recorded on the groove wall of the sound groove. be. Therefore, in order to guarantee this sameness, the main channel signal may be supplied to the level control circuits 13a and 13b via means such as an equalizer. Further, although the above description deals with the case where the present invention is applied to the UM system, it will be easily understood that the present invention can be applied to other systems such as CD-4 and similar benefits can be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an example of a record cutting system for multidimensional audio signals, Figure 2 is a vector diagram of the sub-channel signal encoded in the record cutting system, and Figure 3 shows the recording RIAA characteristics of the main channel signal. 4 is a schematic diagram for explaining a record cutting system for a multidimensional audio signal, FIG. 5 is a block diagram of an example of a record playback system for a multidimensional audio signal, and FIG. 6 is a diagram for explaining a record cutting system for a multidimensional audio signal. Graph showing the disturbance and modulation curve of the sub-channel signal, Fig. 7 is a vector diagram of the difference between the encoded sub-channel signals TT, TQ, Fig. 8
The figure is a block diagram of a record cutting system for producing a record board of the present invention, and FIG. 9 is a block diagram of an example of a record reproducing system. 1 is a sound source, 2 is an encoder, 3 is a recording RIAA characteristic, 6 is an angle modulator, 8 is a 45-45 cutter, 10 is a matrix circuit, 11a, 11b are emphasis circuits, 13a, 13b are level control circuits, 21 is a pickup , 24 is a decoder, 26 is an angle demodulator, and 36 is a modulation curve of the sub-channel signal.

Claims (1)

[Claims] 1. Signals from four directions S _LF , S _RF , S _RB and S _LB
TL＝0.924S _LF ∠＋22.5゜＋0.383S _RF ∠＋67.5゜＋0.383S _RB ∠−67.5゜＋0.924S _LB ∠−22.5゜ TR＝0.383S _LF ∠−67.5゜＋0.924S _RF ∠ −22.5゜＋0.924S _RB ∠＋22.5゜＋0.383S _LB ∠＋67.5 TT=1.414S _LF ∠＋135゜＋1.414S _RF ∠＋45゜＋
1.414S _RB ∠−45゜＋1.414S _LB ∠−135゜ TQ＝1.414S _LF ∠＋90゜＋1.414S _RF ∠−90゜＋
Matrix according to 1.414S _RB ∠ +90° + 1.414S _LB ∠-90°, TL and TR are main channel signals, TT + kTQ and TT - kTQ (k
<1) as an angle modulation sub-channel, one main channel and one sub-channel are recorded on each groove wall of the record board,
Each of the sub-channel signals modulates the uptalk due to the expected tracing distortion error from the main channel recorded on the same groove wall by an index m=rv
ω/S ² (where r is the spherical radius of the regenerated needle tip, v
is the peak velocity of the main channel signal in the sound groove,
ω is the carrier angular frequency, and s is the line angle of the sound groove). 2. The record board according to claim 1, wherein said k is 1/3.