JPS6235117Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic sound envelope adding circuit that can be used, for example, in an electronic music box.

A circuit that utilizes the discharge characteristics of a CR time constant circuit has already been developed as an electronic sound envelope addition circuit. This conventional envelope adding circuit was developed mainly for use in electronic music boxes, and since the sound pressure level of the music box's sound attenuates exponentially, it requires a constant amplitude input of a frequency that corresponds to the pitch of the sound. The sound is attenuated by the discharge curve of the CR time constant circuit, thereby resembling the sound of a music box.

However, the conventional envelope addition circuit described above is
Because the degree of attenuation was always the same regardless of the pitch of the sound, natural music box sounds could not be produced. In other words, the higher the pitch of the music box's sound, the greater the degree of attenuation.
This is because even though the sound does not extend, the conventional envelope adding circuit described above extends the high tones in the same way as the low tones.

Therefore, an envelope storage circuit in which a desired envelope waveform is stored as a digital code, and a timing pulse generation circuit that generates a timing pulse by a pulse obtained by multiplying the sound signal by a certain multiplication ratio are provided. A system has been proposed in which each address of the envelope storage circuit is sequentially specified to sequentially output a digital envelope signal, and this signal is converted from digital to analog. The one described in JP-A-53-3321 is an example of this.

According to the above conventional example, an envelope signal corresponding to the frequency of the sound signal can be obtained, and a natural sound signal can be obtained. However, this method requires an envelope storage circuit, a timing pulse generation circuit, a digital-to-analog conversion circuit, etc., and has the problem of complicating the circuit configuration.

The purpose of the present invention is to change the degree of attenuation according to the frequency of the input sound signal, and by adopting this in an electronic music box, it is possible to produce a sound that closely resembles the sound of a music box. An object of the present invention is to provide an electronic sound envelope adding circuit with an extremely simple circuit configuration.

The feature of this invention is to charge two capacitors, discharge one of these two capacitors, and transfer charge from the other capacitor to one capacitor, thereby increasing the voltage exponentially. By attenuating the sound and changing the cycle of the charge movement in accordance with the frequency of the pitch signal, it is possible to obtain a degree of attenuation that corresponds to the pitch of the sound.

The present invention will be explained below with reference to illustrated embodiments.

In FIG. 1, a melody memory 1 sequentially reads out a melody signal consisting of a pitch signal, a pitch signal, etc. stored in advance, and this melody signal is applied to a note generating circuit 2. The musical note generating circuit 2 processes the reference frequency signal from the reference oscillator 3 in accordance with the melody signal, outputs a musical note signal corresponding to the melody signal, and inputs the signal to the gate control circuit 4.
The gate control circuit 4 processes the reference frequency signal from the reference oscillator 3 according to the pitch of the note signal, and outputs a start signal A consisting of one pulse at the start of the note signal for each note. At the same time, there is a signal B having a frequency corresponding to the pitch of the note signal, and a signal B having the same frequency as this signal B.
A signal C is output at the falling edge of the signal C. The above signal A is a field effect transistor (hereinafter referred to as a field effect transistor) as a switching element.
FET 5 is added to the gate of 5 (referred to as "FET")
is now turned on. A capacitor C ₁ is connected in series to the FET 5, and the capacitor C ₁ is charged by the power supply V _DD when the FET is on. Capacitor _C1 has
Capacitor in parallel via analog switch 6
C ₂ is connected. Capacitor C ₁ has a large capacity, while capacitor C ₂ has a small capacity. The analog switch 6 is turned on by applying the signal C from the gate control circuit 4. capacitor
FET7 as a switching element is connected in parallel to _C2 . The FET 7 is turned on by applying a signal B from the gate control circuit 4 to its gate.
The output of FET7 is added to buffer amplifier 8,
The output of the buffer amplifier 8 is applied to an output amplifier 10 via a level adjustment variable resistor 9, and is outputted from the output amplifier 10 as an audio signal.

Next, the operation of the above embodiment will be explained with reference to FIG. As shown in FIG. 2A, the start signal A is output as one pulse signal for each note signal, and is output at the same time as one note signal is started. Further, as shown in FIG. 2B, the signal B is composed of a pulse signal train having a frequency that determines the pitch based on the musical note signal. Furthermore, as shown in FIG. 2C, signal C consists of a pulse signal train with the same frequency as signal B, but it rises at the same time as signal B falls and does not overlap with signal B. Furthermore, the first pulse signal of the series of pulses forming the signal C is output in synchronization with the signal A.

First, when one start signal A is output from the gate control circuit 4, the FET 5 is turned on only while this signal is being output, and the capacitor _C1 is charged by the power supply _VDD . At the same time, analog switch 6 is turned on by the first pulse of signal C, and capacitor _C2 is also charged by _VDD . capacitor
C ₁ and C ₂ are charged in a short time, and FET 5 and analog switch 6 are immediately turned off. A single pulse of signal B then turns on FET 7, charging the capacitor previously charged at V _DD .
Discharge all the charge in C ₂ and make the terminal voltage of capacitor C ₂ zero. At the same time as one pulse of signal B falls, one pulse of signal C falls, turning on analog switch 6, and turning on the capacitor.
We try to transfer the charging charge of C ₁ to capacitor C ₂ .
However, the pulse width of each signal C is relatively narrow, and capacitor C ₁ has a large capacity while capacitor C ₂ has a small capacity, so the capacitor
Only a portion of the charge on C ₁ is transferred to capacitor C ₂ , and the terminal voltage of capacitors C ₁ and C ₂ at this time becomes V ₂ which is lower than V _DD . Next, when the second pulse of signal B is output and FET 7 is turned on, the charge in capacitor C ₂ is completely discharged, and the terminal voltage of capacitor C ₂ becomes zero. Thereafter, in the same manner, the operation of moving part of the charge from capacitor C ₁ to capacitor C ₂ by turning on analog switch 6 and discharging capacitor C ₂ by turning on FET 7 is repeated. As a result of the above operation, the terminal voltage of the capacitor C ₁ attenuates sequentially as V _DD -V ₂ -V ₃ -V ₄ . . . as shown in FIG. 2D. Further, the terminal voltage signal of the capacitor _C2 , that is, the input voltage signal of the buffer amplifier 8, is a pulse signal with a frequency corresponding to the pitch signal, as shown in FIG.
Similarly, the signal is sequentially attenuated as V _DD -V ₂ -V ₃ -V ₄ . This signal E is amplified via two amplifiers 8 and 10, and then output as audio from a speaker (not shown).

The part on the right side of Figure 2 shows the operation when the pitch is high. As can be seen from this, when the pitch is high, the period of charging capacitor C ₂ by capacitor C ₁ and discharging capacitor C ₂ is short, so the degree of attenuation of signal D and signal E becomes large. Therefore, the higher the pitch, the faster the attenuation occurs, resulting in a sound that approximates a natural sound.

Here, the attenuation operation will be explained using a mathematical formula. Since the initial voltage V ₁ of the signal D is the same as V _DD , V ₁ =V _DD , and the charge Q ₁ at this time is Q ₁ =(C ₁ +C ₂ )V ₁ . Next, the charge of signal D of the second pulse of signal C
Q ₂ is Q ₂ =C ₁ V ₁ = (C ₁ +C ₂ )V ₂ Therefore, the voltage V ₂ at that time is V ₂ =C ₁ /C ₁ +C ₂ V ₁ . Also, the charge Q ₃ of signal D at the third pulse of signal C is Q ₃ =C ₁ V ₂ = (C ₁ +C ₂ )V ₃ Therefore, the voltage V ₃ at that time is V ₃ = (C ₁ / C ₁ + C ₂ ) ² V ₁ . Hereinafter, Qn=C ₁ Vo _-1 = (C ₁ +C ₂ )V _{o Vo} = (C ₁ /C ₁ +C ₂ ) ^n-1 V ₁ , which is an exponential function. Therefore, the decay time changes depending on the density of n (this density corresponds to the frequency), and in this case, the decay time changes in inverse proportion to the frequency.

As is clear from the above explanation, according to the present invention, complicated circuits such as digital envelope storage circuits, timing pulse generation circuits, and digital-to-analog converters are not required, and a combination of simple switching means is sufficient. Therefore, the higher the sound, the faster the attenuation becomes, so the object of the present invention stated at the beginning can be achieved. Also,
According to the present invention, there is an effect that natural sound can be obtained with a relatively simple circuit configuration.

In the embodiment shown in FIG. 1, FETs and analog switches are used as switch elements in consideration of the case where the circuit is integrated into an integrated circuit, but other switch elements may be used instead of these elements.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a timing chart showing the operation of the same embodiment. 4... Gate control circuit, 5, 7... FET as switching means, 6... Analog switch as switching means, C ₁ ... Large capacity capacitor, C ₂ ... Small capacity capacitor.

Claims (1)

[Scope of utility model registration request] A gate control circuit that receives a note signal and outputs a start signal A corresponding to the beginning of a note, a signal B having a frequency corresponding to the pitch, and a signal C having the same frequency as signal B but with a timing shift from signal B. , a switch means operated by signal A, a large capacitor connected in series with this switch means and charged when the switch means is turned on, and a small capacitor connected in parallel with this capacitor. , an electronic circuit connected between both capacitors and having switch means operated by a signal C to transfer the charged charge of the large capacity capacitor to the small capacity capacitor, and switch means operated by a signal B for discharging the small capacity capacitor. Sound envelope addition circuit.