JPS6217302B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal compression and expansion circuit used in a transmission line in which noise is introduced into a signal or in a magnetic recording/reproducing device.

Among transmission media that generally handle audio signals, tape decks that perform magnetic recording and reproduction have an S/N ratio of about 50 to 60 dB due to limitations of magnetic tape and the like. For this purpose, a noise reduction device including a compressor and an expander, a so-called noise reduction device, is used. Among these, a typical one is a noise reduction device called a sum-difference method.

FIG. 1 is a schematic diagram of a noise reduction device using this method. The compressor 1 includes a main signal path 11 that passes the signal X ₁ with a gain of 1, and a transfer function F that nonlinearly transforms the signal X ₁ . (S), each passing signal is added in an adder circuit 13 in a feedforward manner to obtain a level compressed signal Y ₁ , and the main signal path 21 with a gain of 1 is added in an expander. The passed signal is passed through a sub-signal path 22 having a transfer function F(S) and is subtracted by a subtraction circuit 23 in a feedback manner to obtain a level expanded signal _Z1 . In the figure, T is a transmission medium, for example, a magnetic recording/reproducing device such as a tape deck. The relationship between input and output signals at this time is as follows.

_{Y 1} = {1+F(S)}X ₁ Z ₁ = 1/{1+F(S)}Y ₁ Therefore, signal X ₁ = _level expanded signal Z ₁ , and input signal It is what it is.

Furthermore, Fig. 2 shows a specific configuration diagram of the sub-signal path in Fig. 1, including a high-pass filter HPF, a sub-signal path amplifier As, a voltage gain controller VCA with a gain of x connected to the feedback system, and an integrator. It consists of vessel I. The gain x of the voltage gain controller VCA is the output signal
It is controlled by a control voltage Vc obtained by converting the high frequency component of V ₀ (S) into direct current (the direct current converter is not shown). From FIG. 2, the transfer function F(S) of the sub-signal path is as follows.

From this formula, as the VCA gain x changes,
The cut-off angular frequency R ₂ /R ₃ xω ₀ moves, and a frequency characteristic corresponding to the input signal is obtained, and in this type of noise reduction device, the signal after addition or subtraction is 10 dB at maximum at 5 KHz or higher. Now you can get level changes.

However, in such a noise reduction device using a sum-difference method using addition or subtraction, compression and expansion are not performed at high input levels, so saturation of the magnetic tape occurs in the high frequency range, making it difficult to improve the dynamic range. There were disadvantages that I could not get.

The present invention has been made in view of the above-mentioned points, and its purpose is to solve such problems, and to provide a signal that can be compressed and expanded even with high input signals in a high frequency region. This provides a companding circuit.

The present invention will be explained below based on the drawings.

FIG. 3 is a schematic configuration diagram of the present invention. Components that are the same as those in FIG. 1 are designated by the same symbols. In the compressor ₁ , the input signal
(S) and is added in a feedforward manner, and the level compressed signal Y ₂ is
Further, in the expander 2, the signal passing through the main signal path 21' having a transfer function 1/K(S) is converted into a transfer function F.
(S) is subtracted in a feedback manner through the sub-signal path 22, and a level expanded signal _Z2 is obtained.
The relationship between input and output signals is shown in the following equation.

Y ₂ = {K(S)+ _F (S)}X ₂ , Z ₂ = 1/{K(S)+ _{F(S)}Y 2 From} this, signal An output signal Z ₂ identical to ₂ is obtained.

Here, if the transfer _function K(S) is configured as shown in the specific circuit example shown in FIG. S+ _ω1 )/S+
Rω ₁ However, ω ₁ = 1/C ₁ R ₁ , R = 2R ₁ /2R ₁
+ _R2 , and the characteristics shown in FIG. 5 can be obtained. This transfer function K(S) and the transfer function F
The output of addition with (S) has a frequency characteristic shown by the solid line in FIG. 8, and level compression is possible even for high input signals in a high frequency region. The broken line in FIG. 8 is the frequency characteristic of a conventional sum-difference type noise reduction device.

Next, the main signal path transfer function 1/K(S) of the expander can be constructed using a specific circuit example shown in FIG. 1/K(S) is expressed by the following formula.

1/K(S)= _v0 '/vi'(S)=-S+ _Rω1 /
R(S+ω ₁ ) where ω ₁ =1/C ₁ R ₁ , R=2R ₁ /2R ₁
+R ₂ This frequency characteristic is as shown in FIG. 7, and a complementary relationship to that during compression is obtained. FIG. 9 shows the input/output characteristics during compression and expansion at frequency ₁ (Hz) shown in FIG. 8. Note that the broken line represents the input/output characteristics of the conventional noise reduction device.

Note that the frequency characteristics described above are of a low frequency enhanced type on the compression side and a high frequency enhanced type on the expansion side.

As described above, according to the present invention, it is possible to expand the narrow dynamic range in the high range, which is a drawback of magnetic recording and reproducing devices caused by magnetic tapes, heads, etc. This not only provides a significant noise reduction effect, but also has the advantage of preventing distortion due to saturation of the magnetic tape.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a schematic configuration of a conventional noise reduction device, FIG. 2 is a circuit diagram showing a specific configuration of a sub-signal path, and FIG. 3 is a circuit diagram showing an outline of a compression and expansion circuit according to the present invention. 4 and 6 are circuit diagrams showing one embodiment of the main signal path of the compressor and expander in FIG.
FIG. 8 is a frequency characteristic diagram of the main signal path configuration according to FIG.
FIG. 9 is an input/output characteristic diagram during compression and expansion. 1... Compressor, 2... Expander, 11', 21'...
...Main signal path, 12, 22...Sub signal path.

Claims (1)

[Claims] 1 A main signal path through which the signal passes linearly, and a sub-signal path which includes an amplifier, a high-pass filter, a voltage gain controller, and an integrator to transform the signal into a non-linear form, and the main signal path and the sub-signal path The signal level is compressed by adding each signal obtained from the main signal path in a feed-forward manner, and the signal that has passed through the main signal path is subtracted in a feedback manner through a sub-signal path to expand the signal level. In a signal compression and expansion device using the sum-difference method, the compression side is a low-frequency amplification type and the expansion side is a high-frequency amplification type, so that the main signals on the compression side and expansion side have complementary frequency characteristics. A signal companding circuit characterized by: