JPS5914932B2 - Signal dynamic range change circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for changing the dynamic range of a signal, which is an improvement on the invention described in Patent Application No. 24786 of 1972.

The circuits described in the above specification employ a plurality of series connected impedance networks that are voltage driven or current driven in response to an input signal. The output signal is derived from the voltage or current in at least one of the networks, and at least one of the networks is a frequency selective network to achieve dynamic range modification (compression or expansion). Define the limited frequency band in which the test will be performed. A frequency selective network is configured to respond to an increase in the level of a signal component within a limited frequency band by narrowing the limited frequency band and excluding the increased level component from the band. Contains variable circuitry. This effect produces compressor or stretcher characteristics in a manner that will become clear from the description below. The circuit described in the above specification has the disadvantage of using a relatively complex impedance network. The aim of the invention is to eliminate the above-mentioned drawbacks and to use two reactive impedances (
That is, the object of the present invention is to provide a signal dynamic range changing circuit with a relatively simple structure requiring only two capacitors or two inductors) and one resistor network. The circuit according to the invention can be designed as a noise reduction circuit for devices such as inexpensive tape recorders. The invention can be embodied in one of two similar forms depending on whether the circuit is voltage driven or current driven.

According to the present invention, a first circuit comprising a first reactive impedance, a second reactive impedance having the same properties as the first reactive impedance, and a second reactive impedance having the same properties as the first reactive impedance; A second circuit consisting of a series variable resistance circuit,
the second circuit and the first circuit are connected in series between an input terminal and an AC reference potential point to form a voltage divider; the first circuit and the second circuit are coupled; an output circuit for generating an output signal in accordance with a voltage at a point, the output signal having a shelf frequency characteristic with a responsive transition portion, the variable resistance circuit being responsive to the voltage across the variable resistance circuit; When the voltage changes, the resistance value changes,
Thereby, a signal dynamic range changing circuit is provided in which the response transition part of the shelf frequency characteristic shifts to higher or lower frequencies as the voltage increases. The present invention will be described in detail below with reference to the accompanying drawings.

Figure 1 shows a high-frequency compressor (e.g., part of a hiss noise reduction device) used on signals with frequencies above a certain frequency, or a low-frequency expander that acts on signals with frequencies below a certain frequency. 1 illustrates a voltage-driven signal dynamics range modification circuit that can be operated as a rumble noise reduction device (eg, as part of a rumble noise reduction device).

In the illustrated circuit, the first and second reactive impedances are capacitors C1 and C2, respectively;
The series resistor network consists of variable resistor R1. Control circuit CC
detects the voltage across the terminals of the variable resistor R1, provides a rectified and smoothed control signal to the line CS, and this signal controls the value of the variable resistor R1. The variable resistor R1 is, for example, a transistor controlled by the above signal, a FET, or a photosensitive resistor that receives lamp illumination. The general operation of the circuit in Figure 1 is shown in Figure 1a.
This will be explained with reference to the figures.

The frequency response characteristic of this circuit when the value of resistor R1 is large is shown by the solid line in FIG. 1a. The reason why this response characteristic is obtained is as follows. That is, when the frequency is higher than a certain value, the voltage shared by C2 and R1 of the voltage applied to the series circuit of C1, C2, and R1 becomes large, so the output becomes large, and When the frequency is lower than a certain value, the voltage shared by C1 among the voltages applied to the series circuit becomes large, so the output becomes small, and around that certain value of frequency, the response transition part This is because it occurs. In this way, the first circuit is
It has a shelf-like frequency characteristic consisting of a low frequency part, a high frequency part whose level is 10 dB higher than the low frequency part, and a response transition part connecting these parts. As the resistance R1 decreases, the frequency response characteristic shown by the solid line changes from the characteristic shown by the one-dot chain line to the characteristic shown by the broken line, and the response transition portion shifts to the higher frequency side. When the circuit of FIG. 1 is used as a high frequency compressor operating on signals of a frequency higher than a certain frequency, the resistance of resistor R1 decreases as the average voltage across its terminals increases.

For example, at frequency f (the frequency of the vertical dotted line in Figure 1a) 5, the compressor operation is given as follows.

When the signal level is low (e.g. -30 dB), the value of variable resistor R1 is large, so the amount shared between R1 and C2 is large, and the amplitude response at frequency f is high) and is at position P1, at which point, for example, 10 dB There is a boost (BOOst).

When the signal level at frequency f is high (e.g. 0 dB
Since the value of variable resistor R1 is small, R
1 and C2 is small, the response transition part shifts to the high frequency side, and the response at frequency f is low and moves to position P2, and the boost at this point becomes 0. In the middle between the case shown by the solid line in Figure 1a and the case shown by the dashed line in Figure 1a, the characteristics change gradually, and as the signal level increases, a 10 dB boost is applied. gradually shifts to higher frequencies. Compression is achieved by applying a 10 dB boost when the signal level is low and not applying this 10 dB boost when the signal level is high, and reducing the amount of boost when the signal level is at an intermediate level as the signal level increases. After all, shifting the characteristics as shown in FIG. 1a provides compressor operation for high frequency signals. The circuit of FIG. 1, which acts as a compressor for signals of frequencies above a certain frequency, may be combined with the complementary expander of FIG. 2, described below, to provide noise reduction in the high frequency band, such as high frequency tape noise reduction. It can be used as

Furthermore, in the circuit of FIG. 1, a constant resistor R2 can be connected in parallel to the variable resistor R1, thereby providing a lower limit frequency (for example, 1 KHz) at which the compressor action occurs.

Furthermore, the circuit shown in FIG. 1 can be used as a low frequency expander for low frequency signals by increasing the resistance value of the variable resistor R1 in accordance with the rise in the voltage across it.

However, resistor R1 has a fixed upper frequency limit (e.g., 100 Hz) at which stretcher action occurs even at small signal levels.
). For this purpose, if necessary, another resistor can also be provided in series with resistor R1. The operation of this low frequency expander is as follows. At a frequency f below the upper limit frequency (the frequency indicated by the vertical dotted line in FIG. 1a), when the signal level is low, the value of the resistor R1 is small and the response amplitude P2 is at a low position, and the signal level is cut off. When the signal level increases, the resistor R1
The value of becomes large, the response amplitude is at a high position of [1,
Therefore, the signal level is not cut. It will be clear that at intermediate signal levels, intermediate cuts will be made. In this way, a stretcher effect can be provided for low frequencies. The circuit of FIG. 2 is obtained by replacing the capacitors Cl and C2 of FIG. 1 with inductors Ll and L2, in which case the selective high-pass action of the embodiment of FIG. 1 is replaced with a selective low-pass action. As a result, a shelf-like frequency characteristic having a response transition part as shown in FIG. 2a is obtained.

Therefore, the circuit of FIG. 2 can be used as a high frequency stretcher when the value of resistor R1 is controlled to increase as the signal level increases, and conversely the value of resistor R1 decreases as the signal level increases. Can be used as a low frequency compressor when controlled to When the circuit of FIG. 2 is used as a high frequency stretcher, another resistor can be connected in series with resistor R1 to provide a lower frequency limit at which the stretcher action occurs.

Furthermore, when this circuit is used as a low frequency compressor, a constant resistor R2 can be connected in parallel with the resistor R1 in order to provide an upper limit frequency at which the compression effect occurs. As stated above, Figures 1 and 2 operate on the principle of partial pressure.

It is also possible to construct circuits that operate similarly based on the principle of shunting, an example of which is shown below.

FIG. 3 shows an example of a circuit operating on the principle of shunting.

FIG. 3 shows two parallel impedance branches Z1 and Z2.
A general type circuit consisting of is illustrated below. An arbitrary current 1 is supplied to the circuit from a current source (or a voltage source via a series impedance Z5) and is divided into two branches depending on their relative impedance values. If the branch currents are i1 and I2, then 11-Z2×i/(Z1+Z2) and I2=ZlX
A relationship of i/(Z1+Z2) is established, and a large impedance branch path passes a small current, and a small impedance branch path passes a large current. The power can be taken from either of the two branches and is therefore proportional to 11 or I2, depending on which branch it is taken from.

In the illustrated example, a small resistor R3 is connected in series with Z2 to take out an output voltage proportional to I2. Both branches may have variable impedances that vary as a function of signal level;
Preferably, one branch has a fixed characteristic and only the other branch has variable characteristics.

In the illustrated example, the control circuit CC changes Z2 according to the current value 12 flowing through it. The control circuit can rectify and smooth the voltage across R3. This is because this voltage is proportional to I2 or is a voltage that spans Z2 itself.
As with the embodiments of FIGS. 1 and 2, the orientation of controlling Z2 as the current through Z2 increases allows the circuit of FIG. 3 to act as either a compressor or an expander. can. Furthermore, if, for example, by taking the output from I2 a compressed signal is obtained, by taking the output from i1 a decompressed signal can be obtained.6 Preferably, the variable branch Z2 Appropriate controls are used to limit dynamic range changes to low level signal components, for example -20 dB or less, thereby preventing distortion or other undesirable effects on high level signals.

Impedance Z1 and Z2 are capacitors, resistors,
Alternatively, it can be made using only very simple elements such as inductors, but it may be made as a complex circuit network including an active circuit network as necessary.

FIG. 4 shows a specific detailed embodiment of the circuit of FIG. 3, which acts as a high frequency expander operating on signals of frequencies higher than a certain frequency.

The transistor T1 with the resistor R6 has a signal current of 1
This signal current acts as a current source in the fixed branch C3
and a variable branch consisting of C4, R4 and R5.
The output signal is derived from the current 12 in the variable branch, with transistor T2 acting as a current-to-voltage converter. Power supply impedance Z5 is provided by T1. At low frequencies, the capacitive reactance of C3 and C4 is large.

Therefore, essentially the entire human power current flows through resistor R4 to provide the output signal. The control circuit CC reduces the value of R5 from its initial value at a very low level. The initial value of R5 is selected to have a very large resistance value. At high frequencies, the capacitive reactance of C4 will be much smaller than R4, and the input current will be shunted between C3 and C4 according to their capacitance ratio. For example, C3=2.16×C
4, most of the current with frequencies higher than a certain frequency is shunted to C3, and the current in C4 is 1 less than the input current.
0 dB, thereby providing a stretching effect for signals of higher frequencies than a certain frequency. For high level high frequency signals, the control circuit reduces R5, which causes the fourth
The transition part of the characteristic shown in Fig. 4a is shifted to the higher frequency side, and the band in which the expansion is performed is narrowed as shown in Fig. 4a. The circuit may be constructed by replacing capacitors C3 and C4 with inductors.

Complementary characteristics can be obtained by connecting a compressor or expander according to the invention to the negative feedback loop of a high gain amplifier.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 1a is a diagram showing the characteristics of the circuit in FIG. 1, FIG. 2 is a circuit diagram of another embodiment of the present invention, and FIG. Diagram showing the characteristics of the circuit shown in Figure 3.
4 is a diagram showing another embodiment of the present invention, FIG. 4 is a diagram showing a circuit embodying FIG. 3, and FIG. 4a is a diagram showing characteristics of the circuit of FIG. 4. Cl, C2: Capacitor, Ll, L2: Inductor, R
1: variable resistance, R2: fixed resistance, CC: control circuit.

Claims (1)

[Claims] 1 In a circuit for changing the signal dynamic range, (a) the first reactive impedance C1
or L1; (b) a second reactive impedance C2 or L2 having the same properties as the first reactive impedance; and a variable resistance circuit R1 in series with the second reactive impedance.
(c) a second circuit comprising: a second circuit, wherein the second circuit and the first circuit are connected in series between an input terminal and an AC reference potential point to form a voltage divider; an output circuit that generates an output signal according to a voltage at a coupling point between the first circuit and the second circuit, the output signal having a shelf-like frequency characteristic having a response transition portion; d) The variable resistance circuit changes resistance value when the voltage changes in response to the voltage across the variable resistance circuit, thereby causing the response transition portion of the shelf-like frequency characteristic to change as the voltage increases. A signal dynamic range modification circuit consisting of shifting the signal to a higher frequency or to a lower frequency.