JPS6016638B2 - Frequency-voltage conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved frequency-voltage conversion circuit suitable for use in, for example, a guitar synthesizer.

2. Description of the Related Art Conventionally, a guitar synthesizer as shown in FIG. 1 has been known as a device for converting a signal input from a guitar into a musical tone signal exhibiting a tone different from the original guitar tone and generating the sound.

In FIG. 1, 10 is a string vibration detector such as a guitar pickup that detects guitar string vibration and converts it into a vibration signal 10S, and 12 is a string vibration detector that extracts the fundamental wave from the string vibration signal 10S. A fundamental wave-to-square-wave conversion circuit converts this into a rectangular-wave signal 12S, and 14 is a frequency-to-voltage (f/V) conversion circuit to convert the rectangular-wave signal 12S into a voltage signal 14S having a magnitude corresponding to its frequency. , 16 is a sound source signal 16 whose oscillation frequency is controlled according to the voltage signal 14S.
a voltage-controlled variable frequency oscillator (VCO) that generates S;
18 is a voltage-controlled variable filter (VCF) for imparting a tone different from the original guitar sound to the sound source signal 16S;
, 20 is a voltage-controlled variable gain amplifier (VCA) for imparting a desired amplitude envelope to the musical tone signal 18S from the VCF 18, and 22 is an output amplifier for generating the musical tone signal 20S from the amplifier 20 as a musical tone. This is a sound system that includes speakers, etc. Note that 24 is an envelope follower for rectifying the string vibration signal 10S and extracting its amplitude envelope, and the envelope signal 24S as its output is sent to the VCF 18 and VCA 2.
0' is added as a cutoff frequency control input and a gain control input, respectively. By the way, in the above-mentioned type of synthesizer, in order to form the voltage 14S corresponding to the pitch (pitch) of the played string tone, the square wave signal 12S from the fundamental wave-square wave conversion circuit 12 is converted to an f/V conversion circuit. However, since the period of the rectangular wave signal 12S may not correspond accurately to the period of the fundamental wave of the string vibration signal 10S, the voltage signal 14S for VCO control is not played. There was an inconvenience in that the pitch was different from the pitch of the string tone.

Until now, as the fundamental wave-rectangular wave conversion circuit 12, the second
As shown in Fig. 2a, the input signal 10S is amplified and clipped by a high gain amplifier, and as shown in Fig. 2b, the zero cross of the input signal 10S is detected.

A cross trigger signal 11S is created and a flip-flop is controlled by this signal 11S, and a second c
As shown in the figure, a waveform signal that follows the rising waveform of the input signal 10S but does not follow the decay waveform is created using a charging/discharging circuit, and this waveform signal and the input signal 10S are compared every positive and negative half cycle. , and the comparison outputs 11S, , 11S2 are used to control a flip-flop. However, in these conversion circuits, since the waveform of the input signal 10S changes temporally due to the temporal phase shift of the emotional sound component, etc., the waveforms shown with * marks in FIGS. 2a to 2c, respectively. Therefore, it was impossible to avoid that the rectangular wave signal 12S as the conversion output contained a signal component having a frequency approximately twice that of the fundamental wave. This kind of signal component is f/
Since the output level of the V conversion circuit 14 is instantaneously increased, the VCO 16 is controlled with a control voltage that does not correspond accurately to the pitch of the string tones being played, and as a result, the sound produced by the sound system 22 is The pitch fluctuated rapidly and undesirably, making the musical sound extremely distorted and distorted. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved frequency-to-voltage conversion circuit capable of eliminating the drawbacks of the prior art described above.

The frequency-voltage conversion circuit according to the present invention is characterized by providing means for detecting a disturbance in the cycle of the input signal, and when a disturbance in the cycle is detected, the operation of capturing and holding the converted voltage is prohibited. At the point.

According to a frequency-voltage conversion circuit having such characteristics, it is possible to output only the converted voltage corresponding to a normal cycle, so that accurate pitch can be obtained regardless of malfunction of the fundamental wave-square wave conversion circuit. voltage can be formed.
The invention will now be described in detail with reference to embodiments shown in the accompanying drawings.

FIG. 3 shows details of the pitch voltage forming section in a guitar synthesizer according to an embodiment of the present invention. Therefore, illustration is omitted, and the same parts as in FIG. 1 are given the same reference numerals.

The signal waveforms at each part a to r in Fig. 3 are shown in Fig. 4 a to r.
are shown respectively. The illustrated pitch voltage forming section includes a fundamental wave to rectangular wave conversion circuit 12 and an f/V conversion circuit 14, and the conversion circuit 12 inputs the string vibration signal a and converts it into the period of the fundamental wave. A conversion circuit 14 generates a rectangular wave signal f having a corresponding period and a signal g obtained by dividing this signal f by 1/2, and uses these signals f and g as input to determine the pitch of the tone to be supplied to the VCO. A voltage signal 14S is generated.

The fundamental wave to rectangular wave conversion circuit 12 is provided with rectifier circuits RC, RC2 that half-wave rectify the input signal a as shown in FIG. The rectified outputs from RC, , RC2 are supplied to corresponding charging/discharging circuits CD, , CD2, respectively.

The charging/discharging circuits CD, CD2 each consist of parallel circuits of a capacitor and a resistor, and as shown in Fig. 4b and c, respectively, they follow the rising waveform of the input signal a every positive and negative half cycle, but the waveform is attenuated. Waveform signals b and c that do not follow the waveform signals b and c are respectively generated. These waveform signals b, c are supplied to one input terminal of each of the comparators CM, CM2, and the input signal a is supplied to the other input terminal of each of the comparators CM, CM2. Therefore, the comparators CM, CM2 compare the waveform signal b and the input signal a, and the waveform signal c and the input signal a, and generate a pulse every time the comparison inputs match. The pulses generated from each comparator CM, CM2 at this time are shown in FIG. I will call it that. The fundamental wave pulse signals d and e are applied to the set input terminal s and reset input terminal R of the R-S flip-flop RF, respectively. A rectangular wave signal f having a period corresponding to the fundamental wave period as shown in FIG. 4f is taken out from the output terminal Q of the flip-flop RF. This rectangular wave signal f is converted into a signal g having a frequency of 1/2 of the signal f in a 1/2 frequency divider FD. Rectangular wave signals f, g as shown in Fig. 4 f, g, respectively
is supplied to the f/V conversion circuit 14. f/V conversion circuit 1
4 includes a voltage generator 14A that receives the rectangular wave signals f, g as input and generates a period-corresponding voltage i having an amplitude corresponding to the period of the rectangular wave signal g; A voltage storage section 14B consisting of a sample and hold circuit that takes in and holds i, an integrating section 14C consisting of a Miller integrating circuit that integrates a rectangular wave signal g, and an integral output m from this integrating section 14C within a predetermined error range. A comparison section 14D that performs a comparison calculation to see if there is a difference, and a control section 14E that generates control signals 1 and k for controlling the operations of the integration section 14C and the comparison section 14D, respectively, are provided.

A system including the integrator 14C, the comparator 14D, and the controller 14E compares adjacent high-level durations and low-level durations of the rectangular wave signal g to detect whether there is any period disturbance in the rectangular wave signal g. , when there is a period disturbance, the voltage storage unit 14
This is provided to prohibit the conversion voltage from being taken into B. The voltage generator 14A is provided with a capacitor C, which is charged by a constant current source lo through a gate ○, which is controlled by a rectangular wave signal g, and a discharge path is provided in parallel to this capacitor C. Gate G2 is connected.

The control signal h for controlling the gate G2 is a signal obtained by inverting the rectangular wave signal f by the inverter W, and a signal obtained by inverting the rectangular wave signal g by the inverter IV2.
, is formed in the form shown in FIG. 4h. Capacitor C starts charging at the rising edge of rectangular wave signal g, and discharges every time control signal h becomes high level, so that a period-corresponding voltage i as shown in Figure 4 i is applied to the terminals of capacitor C. can get. This period-corresponding voltage i is supplied to the voltage storage section 148 via the buffer BF. The voltage storage unit 14B includes a sampling gate ○3, a sample holding capacitor C2, and a buffer B.
It is composed of a sample and hold circuit including F2.

The control signal r for controlling the gate G3 is obtained by ANDing the rectangular wave signal f and the signal obtained by inverting the rectangular wave signal g by the inverter IV2, so that the fourth
While generating the control signal i as shown in FIG.
C, a control signal q indicating that there is a period disturbance in the rectangular wave signal g is generated from a system including the comparison unit 14D and the control unit 148, and the control signals i and q are ANd by an AND gate AG3.
D, it is formed in the shape shown in FIG. 4r. If there is no period disturbance N in the rectangular wave signal g, the control signal q will be at a high level, so the gate 3 is controlled to open every time the control signal i becomes a high level. Therefore, the capacitor C3 holds the voltage signal i in synchronization with the rectangular wave signal g at a period approximately twice the fundamental wave period. On the other hand, if there is a periodic disturbance N in the rectangular wave signal g, the control signal q will take a low level as shown by QN due to the effect of the system of 14C to 1 criminal, so the control signal r will change to this low level. During the level period, you will not take a high level. Therefore, since the gate G3 remains closed during this low level period, the undesired voltage VN generated as a result of f/V conversion despite the period disturbance N is not sampled. There is no hold. Therefore, as the output 14S of the f/V conversion circuit 14, a voltage output corresponding to the fundamental wave period or fundamental frequency, which does not include the voltage VN corresponding to the period disturbance N, is obtained, and this output 14S is used for control. VC to be
○ (Fig. 1, 16) is no longer subject to deliberate control. Next, regarding the system that generates the control signal q, the integrating section 14C consists of a Miller integrating circuit that includes an obeamp OP, a capacitor C3 and a resistor R for determining a time constant, and a reset gate G4. There is.

The comparison unit 14D also includes a comparator CM3 that compares the integral output m and the output +ΔV of the variable resistor P, and a comparator CM3 that compares the integral output m and the output −ΔV of the variable resistor P2.
4, and the respective comparison outputs are connected to diodes D2 and D3.
The AND output p is supplied to the data input terminal D of the D-flipflop DF. Furthermore, the control unit 14E includes a transistor Q that outputs a control signal k including a pulse synchronized with the falling timing of the rectangular wave signal g to the collector side, and a control signal including a pulse synchronized with the falling timing of the control signal k. 1 on the collector side, and the control signal 1 is sent to the reset gate G via the diode D.
4, the control signal k is connected to the trigger input terminal of the D-flip-flop DF. In such a configuration, an output m obtained by integrating the rectangular wave signal g is obtained from the integrating section 14C as shown in FIG.

The comparator 14D checks whether the value of the integral output m is within the range of 2ΔV, (2ΔV,) as shown in FIG.
Signals n and o indicating the result are generated, and an output p obtained by performing an AND operation on these signals n and o is jointly supplied to the D-flip-flop DF. Since the D+ flip-flop DF is triggered by the control signal k as shown in FIG. 4, it inverts its state when the data input p goes low and the control signal k goes low; A control signal q having a low level QN as shown at q is generated at output Q. Since the control signal k is synchronized with the falling timing of the rectangular wave signal g as described above, the timing at which the control signal q becomes the low level QN is the voltage VN of the control signal i.
It is synchronized with the rise of the acquisition pulse JN, and therefore,
By ANDing the control signals q and i with the AND gate AG3, the AND output r, that is, the control signal for the gate G3, can be obtained as a signal that does not include the pulse JN for capturing the voltage VN. Prohibited operations become possible. In the circuit shown in FIG. 3, the period comparison result is 2AV. If it falls within the range of , the f/V conversion voltage is taken in, but in the range of 2△V, it is necessary to take in the f/V conversion voltage when the fundamental frequency of the input signal changes. Therefore, it cannot be set too small.

On the other hand, if the range of 2ΔV is made too large, when the input fundamental wave frequency increases, the corresponding period comparison result will always fall within the range of 2ΔV, and the circuit will no longer function as expected. Therefore, it is desirable to control the integrated output waveform according to the frequency of the input signal. For this purpose, for example, the output level of the 1/2 frequency divider FD (the amplitude level of the signal g) may be changed depending on the input signal frequency,
The values of the integrating resistors R and capacitor C3 can be changed. In particular, in a guitar synthesizer, when the circuit shown in Fig. 3 is provided for each string, L2△
It is possible to set the range of V, in advance and not change it, but if you install one circuit for all strings, the input frequency range will be large, so the sound that is repelled will be It is a good idea to detect which string corresponds to the string and then switch the above-mentioned quantities.
As described above, according to the present invention, even if the fundamental wave to rectangular wave conversion circuit generates a rectangular wave output including a signal component corresponding to an undesirable overtone period, the f/V conversion circuit Since the converted voltage corresponding to the output voltage is not output, accurate and stable pitch voltage can be obtained.
Erroneous control of VCO etc. can be effectively prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional guitar synthesizer, and FIGS. 2a to 2c are waveform diagrams for explaining the operation of different types of conventional fundamental wave to rectangular wave conversion circuits, respectively.
FIG. 3 is a circuit diagram showing details of a pitch voltage forming section in a guitar synthesizer according to an embodiment of the present invention, and FIG. 4 is a waveform diagram of each part to explain the operation of the circuit of FIG. 3. It is. 14... Frequency-voltage conversion circuit, 14A...
... Voltage generation section, 14B... Voltage storage section, 1
4C...Integration section, 14D...Comparison section,
14B...Control unit. Figure 2q Figure 2b Figure 2c Figure 1 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A voltage generating section that receives a rectangular wave signal as input and generates a period-corresponding voltage having an amplitude corresponding to the period of the rectangular wave signal; In a frequency-voltage conversion circuit, the frequency-voltage conversion circuit includes a voltage storage unit that takes in and holds the voltage, and extracts the voltage held in the voltage storage unit as a frequency-voltage conversion output, and means for detecting a disturbance in the period of the rectangular wave signal. 1. A frequency-voltage conversion circuit comprising: a frequency-to-voltage conversion circuit which prohibits the voltage corresponding to the period from being taken into the voltage storage section when a disturbance in the period is detected. 2. In the frequency-voltage conversion circuit according to claim 1, the means for detecting a disturbance in the period of the rectangular wave signal detects adjacent high level duration and low level duration in the rectangular wave signal. A frequency-voltage conversion circuit, characterized in that it is configured to detect periodic disturbances by comparison.