JPS5837112Y2 - Envelope signal forming circuit - Google Patents

Description

[Detailed description of the invention] This invention can be used, for example, in a guitar synthesizer that picks up string vibrations and converts the signal into a different tone color signal to produce sound, or in a normal keyboard-type music synthesizer, which uses a microphone input signal such as voice to adjust the volume. The present invention relates to an envelope follower used to control pitch, timbre, etc., that is, an envelope signal forming circuit that obtains an envelope waveform of an input signal.

As shown in FIG. 1, a conventional envelope signal forming circuit generally includes a rectifier 1 consisting of a diode D that rectifies a human input signal, charges the rectified output through a charging path formed by a resistor R1, and charges the rectifier 1 through a charging path formed by a resistor R1. and an integrator 2 consisting of a capacitor C discharging via a discharge path by R, ).

When an input signal such as A is input to the input terminal IN, an envelope signal that follows the amplitude of the input signal such as B is output to the output terminal OUT.

Incidentally, in such an envelope signal forming circuit, in order to reduce ripples in the output signal, it is necessary to increase the time constant of the charging path, which is determined by the values of the resistor R1 and the capacitor C in the integrator, to a certain extent.

In this way, when the input signal level suddenly increases, for example when the input signal rises from nothing to something, the charging time constant of the integrator is large, so that the sudden input signal envelope is There was a drawback that it could not follow the rise.

This invention attempts to solve the above-mentioned drawbacks by changing the charging time constant of the charging path of the integrator in the envelope signal forming circuit into a relatively large first time constant and a relatively small second time constant. In addition, a fast rise detector is provided to detect a sudden rise in the human input signal envelope and control switching of the charging time constant of the integrator, and the charging time constant of the integrator is normally set as the first time constant. , the followability of the envelope follower is improved by switching to the second time constant only when the high-speed rise detector detects a sudden rise of the human input signal envelope.

Embodiments of this invention will be described below with reference to FIGS. 2 to 4.

FIG. 2 shows a basic embodiment of this invention, and the same parts as in FIG. 1 are given the same reference numerals.

In this embodiment, a series circuit consisting of a resistor r1 and a switching element S1 such as an FET is connected in parallel to the resistor R1 of the charging path of the integrator 2, and a high-speed rise signal that detects a sudden rise of the input signal envelope is connected in parallel to the resistor R1 of the charging path of the integrator 2. A detector 3 is provided,
The output is used to control on/off of the switch element S1.

Next, the operation of this embodiment will be explained.

Switch element S1 is normally off, and integrator 2
The capacitor C is charged only through the resistor R1, and its charging time constant C, R, is relatively large.

When the fast rise detector 3 detects a sudden rise in the input signal envelope, the output signal turns on the switch element S, and the resistor r1 is connected in parallel to the resistor R1.

Therefore, the combined resistance value of the charging path is R1·r1/(R1+r1), where R1 and rl are the resistance values of each resistor, which is smaller than the value of resistor R1.

If rt<Rt, the change becomes large.

Therefore, the time constant at this time is C・R1−r 1/(R1+
r t) is smaller than the normal charging time constant CR, and can substantially follow the sudden rise of the human input signal envelope.

FIG. 2 is a circuit diagram showing only an integrator according to another embodiment of the invention.

In this embodiment, a resistor r'1 is connected in series with a resistor R'1, and a switch element S1 is connected in parallel.

The switch element S1 is normally off, and the capacitor C is charged through the series circuit of the resistor R1 and the resistor r/1.

The resistance values of resistor R'l and resistor r'1 are selected so that the time constant C·(R'l+r'i) at this time has a value similar to the charging time constant of the conventional envelope follower.

In this case, as in the optical embodiment, when the fast rise detector 3 detects a sudden rise in the input signal envelope, the output signal turns on the switch element S1, and the resistor R'
l is short-circuited, and the resistance of the charging path becomes only the resistance r/1.

Therefore, the charging specific time C-r'1 is smaller than usual and can approximately follow the sudden rise of the input signal envelope.

FIG. 4 is a circuit diagram showing a more specific embodiment of this invention, and the same parts as in FIG. 2 are given the same reference numerals.

In the figure, 4 is a level detector that detects when the input signal level has fallen below a predetermined value, and 5 is a bypass filter (to reduce the influence of noise by passing only the desired frequency band of the input signal). 6 is a buffer amplifier.

PS, ~PS4 are phase shifters, and 11 is an instantaneous maximum level signal extractor in place of the rectifier 1, which is a diode that receives the output signal of the buffer amplifier 6 and the output signals of the cascade-connected phase shifters PS1 to PS4, respectively. It is composed of diodes D1 to D5, and the negative electrode sides of these diodes D1 to D5 are commonly connected.

Therefore, only the signals at the input signal level of each of the diodes D1 to D5 are rectified and output at each instant.

7 is a buffer amplifier, 8 is an inverter, 9 is a differentiator, and 10 is an inverter.

In the above embodiment configured in this way, the input terminal I
An input signal from a microphone or the like inputted from N is inputted through a bypass filter 5, its level is adjusted by a variable resistor R1, and inputted through a buffer amplifier 6 to a diode D1 of an instantaneous maximum level signal extractor 11.

In addition, the output signal of the buffer amplifier 6 is transmitted through phase shifters PS1 to P
The phase of the signal is sequentially shifted slightly by step S4 and input to each of the diodes D2 to D5, and the momentary maximum level signal among them is rectified and outputted and guided to the integrator 2.

For example, if the output signal of the buffer amplifier 6 is a signal as shown in FIG.

On the other hand, the fast rise detector 3 rectifies the input signal as shown in A with a diode D6, and rectifies the input signal as shown in A with a capacitor C1 and a resistor R4.
The envelope waveform signal shown in Figure 8 is smoothed by , and this is differentiated by a differentiating circuit consisting of a capacitor C2 and a resistor R5, and a pulse signal corresponding to the rising speed of the input signal envelope as shown in Figure 2 is sent to a comparator C.
Lead to the positive input terminal of P1.

A variable resistor is attached to the negative input terminal of comparator CP1.
A positive reference voltage preset by R2 is applied.

The output of the comparator CP1 set in this way is always a negative voltage as shown in E, and is inverted only when a pulse larger than the reference voltage is input, that is, when the input signal envelope rises suddenly. It becomes a positive voltage.

Therefore, since the diode D7 is normally forward biased and conductive via the resistor R3, a negative voltage is applied to the gate of the FET switch element S1, and the switch element S1 is turned off.

When the human input signal envelope suddenly rises, diode D7 is reverse biased and becomes non-conductive, so a positive voltage is applied to the gate of switch element S1 via resistor R3, turning switch element S1 on. becomes.

As a result, the charging time constant of the charging path of the integrator 2 is reduced during this period, and the ability to follow a sudden rise in the input signal envelope is improved.

After this period, the switching element S1 is turned off again to increase the charging time constant and reduce ripple.

Next, the level detector 4 inputs an input signal such as A as a positive input to a comparator CP2 which uses a negative reference voltage preset by a variable resistor VR3 as a negative voltage via a resistor R6, and its output is connected to a diode D8. When the input signal level is greater than the absolute value of the reference voltage, a negative signal as shown in Figure 1 is obtained, and this is smoothed by an integrating circuit consisting of resistors R7 and Rs and capacitor C3, as shown in Figure 3. A negative signal is output.

Therefore, since the switch element S2 is off while this negative signal is being output, the discharge time constant is large and no ripple occurs because there is only the resistance R2 in the discharge path of the integrator 2.

When the input signal level attenuates below the set value, the negative output signal of the level detector 4 disappears and the gate of the switch element S2 becomes OV, so the switch element S2
is turned on, and the resistance of the discharge path of the integrator 2 becomes a parallel resistance of the resistor R2 and the resistor r2.

Therefore, the discharge time constant becomes small, and it becomes possible to follow the subsequent rapid attenuation of the human power signal level (when the string stops vibrating, when the vocalization stops, etc.).

In this way, from the integrator 2, an envelope signal with few knots and good followability as shown in H is obtained, and this envelope signal is further impedance-converted via the buffer amplifier 7 and sent to the first output. Terminal 0
Output to UT1.

Further, the signal inverted via the inverter 8 is output to the second output terminal (inverted output terminal) OUT2, and the rising pulse of the envelope waveform differentiated by the differentiator 9 is output to the third output terminal (inverted output terminal) OUT2.
output terminal (trigger output terminal) OUT3.

Furthermore, the output pulse of the differentiator 9 is inverted by an inverter 10 and outputted from a fourth output terminal (inversion trigger output terminal) OUT4.

Each of these outputs is used depending on the purpose.

Condenser C constituting the integrator 2 in this embodiment
An example of specific numerical values of the capacitance and the resistance value of each resistor is as follows: C=1 p F , R1=50 KQ , r 1=1
0 KQ, R2=IMQ, r2=500 KQ
, R3,”, 10 KQ.

However, resistance R1, r1. R2 and r2 use variable resistors that can be adjusted as appropriate.

As explained above with respect to the embodiment, according to this invention, a sudden rise in the input signal envelope is detected and the charging time constant of the integrator is reduced only at that time, so that it has good followability against sudden rises. , an envelope signal with less ripple can be obtained.

Furthermore, as in the embodiment shown in Fig. 4, the discharge time constant of the integrator can be switched and controlled, and if the discharge time constant is made smaller when the input signal level falls below a certain set value, the subsequent It can also follow sudden attenuation of the input signal (such as when the human input signal suddenly disappears).

In addition, if the phase of the input signal is shifted little by little using multiple phase shifters connected in series, and the momentary maximum level of the signal is integrated, the frequency range of the input signal can be widened, and tracking performance is even better. , an envelope signal with less ripple can be obtained.

If the musical tone of a guitar synthesizer or keyboard-type music synthesizer is controlled using the envelope signal obtained by such an envelope signal forming circuit or its reverse signal, the envelope of the input signal such as string vibration or voice as a control signal can be controlled. It can be controlled faithfully and is extremely effective.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional envelope signal forming circuit, Fig. 2 is a circuit diagram showing an embodiment of this invention, and Fig. 3 is a circuit diagram showing only the integrator portion in another embodiment of this invention. FIG. 4 is a circuit diagram showing a more specific embodiment of this invention. 1... Rectifier, 2... Integrator, 3...
...High-speed rise detector, 4...Level detector, 5...Bypass filter, 6,7...
... Buffer amplifier, 8, 10 ... Inverter, 9
... Differentiator, Sl, S2 ... Switch element, PS1 to PS4 ... Phase shifter, CP, CP
2...Comparator.

Claims (1)

[Scope of utility model registration request] In an envelope signal forming circuit that includes a rectifier that rectifies an input signal and an integrator that charges the rectified output through a charging path and discharges it through a discharging path, the charging time constant of the charging path of the integrator is A means is provided for switching between a relatively large first time constant and a relatively small second time constant, and the charging time constant of the integrator is controlled to be switched by detecting a sudden rise in a human signal envelope. a fast rise detector is provided, the charging time constant of the integrator is always the first time constant, and the second time constant is set only when the fast rise detector detects a sudden rise of the input signal envelope. An envelope signal forming circuit characterized in that the envelope signal forming circuit is configured to switch.