JPS5931720B2 - Octave conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an octave conversion method for musical tones suitable for use in electric pianos and the like.

Conventionally, in order to octave convert a musical tone signal having the timbre of a certain musical instrument, the fundamental waveform and envelope waveform were separated, the fundamental wave was divided to reduce the frequency, and then envelope shaping was performed. This method requires a complicated circuit configuration, and it is difficult to obtain a high-fidelity sound similar to the original sound. In order to solve these conventional problems, the applicant has proposed an octave conversion method that generates a musical tone signal that has the same envelope as the original sound signal and whose fundamental wave is one or more octaves lower. (Japanese Patent Application No. 53-34540
No. 27301)).

This octave conversion method involves inputting a sound source signal obtained by electrically detecting the mechanical vibrations of a musical instrument and a modulation signal having, for example, half the frequency of the sound source signal into a voltage-controlled amplifier, multiplying the sound source signal, and modulating the sound source signal. The frequency difference between the signals is calculated to obtain a musical tone signal that is, for example, one octave lower than the sound source signal. In this case, the even harmonics of the fundamental wave of the octave-converted musical tone signal are extracted without converting the frequency of the sound source signal by using the leakage signal of the voltage control amplifier or by mixing the sound source signal directly to the output. I was getting it. Therefore, the even harmonics have exactly the same envelope as the original sound signal. In general, sounds caused by mechanical vibration have a shorter decay time for the harmonic envelope than the fundamental wave, but musical tone signals obtained by the above-mentioned octave conversion method have harmonic envelopes that have the same decay time as the fundamental wave envelope. Because of this, it had the disadvantage that it was not possible to obtain a tone close to natural sounds, especially when the volume was high to a certain extent, such as at the start of the sound. This invention was made in view of the above points, and its purpose is to produce a tone that is close to natural sounds by generating many even-order harmonics at the rise of a sound, and by shaping it with an envelope different from the original sound signal. An object of the present invention is to provide an octave conversion method that allows a musical tone signal having the following characteristics to be obtained.

In order to achieve such an objective, the present invention operates an envelope generation circuit to generate a nip rope signal when the sound source signal is at a predetermined level or higher, adds this envelope signal to a modulation signal, and inputs it to a voltage control amplifier. It was designed to do so.

Hereinafter, this invention will be explained in detail based on examples.

FIG. 1 is a block circuit diagram of an octave conversion circuit using an embodiment of the octave conversion method according to the present invention.

When a sound source signal obtained by picking up string vibrations of an electric piano or the like is input from an input terminal Ti, a predetermined frequency of this sound source signal is emphasized by a filter 1 and then input to a voltage control amplifier (VCA) 2.

On the other hand, when a rectangular wave modulation signal oscillated by an electronic circuit is input to the modulation input terminal Tm, unnecessary harmonics are removed from this modulation signal by the filter 3, and the waveform becomes close to a sine wave and is passed through the mixing circuit 4. It enters the voltage controlled amplifier 2. As a result, the sound source signal is multiplied by the modulation signal and subjected to octave conversion, and after unnecessary high-order harmonics are removed by the filter 5, the musical tone signal octave converted from the sound source signal is sent to the output terminal T. is output from. At this time, voltage control is increased. Since the spanner 2 also has a so-called addition function in which a part of the input signal is output as a leakage signal, a part of the sound source signal is not octave converted and enters the musical tone signal as it is and is sent to the output terminal T. is output from. Furthermore, here,
Filter the leakage signal as necessary. It can also be removed or attenuated with an attenuator. Here, before going into the explanation of the envelope generation circuit, the basic operation of octave conversion in the voltage control amplifier 2 will be explained using equations.

Now, the characteristics of the voltage control amplifier 2 are set as follows.

(However, VO = musical tone signal voltage, Vi = sound source signal voltage,
A = amplification degree, Vm = modulation signal voltage, α, C = constant) Here, if the fundamental frequency of the sound source signal is Fi and the frequency of the modulation signal is Fm, the sound source signal voltage Vi and the modulation signal voltage V
m becomes the following formula.

(However, E(t) is a function indicating the envelope of the sound source signal.) Substituting equations (2), (3), and (4) into equation (1) yields the musical tone signal voltage V.

becomes like the following formula. Therefore, the musical tone signal voltage V.

As a result, a voltage having the same envelope as the sound source signal and consisting of a frequency component of (Fm+Fi), a component of (Fm-Fi), and a component of Fi is obtained. Now, the frequency Fm of the modulation signal is the fundamental frequency Fi of the sound source signal.
If we set half of that, that is, Fm=-U, then equation (5) becomes as follows.

That is, by emphasizing the (-) component with the filter 5, a musical tone signal that has the same envelope as the sound source signal and whose fundamental wave frequency is (-υ-1) is one octave lower than the sound source signal can be obtained.

In addition to this fundamental wave, the musical tone signal also has a frequency Fi of 2.
Overtones include components of the third harmonic of frequency (-Fi). If the sound source signal and modulation signal contain harmonics, the musical tone signal will contain higher-order harmonics. Here, the term [CE(t)Sin2πFit] in equation (6) corresponds to the second harmonic signal voltage.

Since this signal forms the same envelope as the sound source signal due to E(t), by temporally changing the constant C, it is possible to form this signal with a different envelope from the sound source signal. That is, after a part of the sound source signal enters the rectifier circuit 6 and is rectified, the comparator 7 compares its level with a constant threshold voltage.

When this rectified voltage becomes larger than the threshold voltage, an output is output from the comparator 7, and the envelope generating circuit 8 operates to generate an envelope signal. This envelope signal has a fast rise and decays exponentially, and the decay time is set to be shorter than the envelope of the musical tone signal. The envelope signal from the envelope generation circuit 8 is combined with a modulation signal in the mixing circuit 4, and the combined output is input to the voltage control amplifier 2.
The constant C in the voltage control amplifier 2 changes over time in accordance with this envelope signal, and the bias voltage changes, so that the second harmonic signal voltage forms an envelope. Note that if even-numbered harmonics other than secondary overtones are also included, envelopes are formed in the same way. FIG. 2 is a circuit diagram of a specific embodiment of the envelope generating circuit portion.

The musical tone signal rectified by a rectifier circuit 6 consisting of a capacitor, a resistor, and a diode is input to a comparator 7, where it is compared with a threshold voltage Vth. The output of the comparator 7 is always ``H'', but when the rectified musical tone signal becomes higher than the threshold voltage Vth, it momentarily becomes ``L'', and after this rectangular wave is differentiated by the differentiating circuit 8a, the calculation The signal is amplified by the amplifier 8b and becomes an envelope signal. An envelope generating circuit 8 is constituted by a differentiating circuit 8a and an operational amplifier 8b. Note that the diode D is connected to remove positive pulses. FIG. 3 is a waveform diagram of each signal.

A shows the waveform of the sound source signal, and A shows the waveform of the octave-converted musical tone signal fundamental wave. The musical tone signal has the same envelope as the sound source signal. C shows the waveform of even harmonics of the musical tone signal, but it has a different envelope from that of the sound source signal. In this way, by forming the envelope of overtones so that they become louder at the rise of a sound and decay faster than the decay of the fundamental wave, the octave-converted musical tone signal will have a more so-called sense of attack and a tone that is closer to natural. Experiments have shown that rather than creating a sense of attack by making the envelope of the entire signal into a double attenuation waveform, it is clearly more natural to create a double attenuation waveform by forming harmonics into a separate envelope and then adding them as in this example. I felt a sense of attack. In the embodiment, the tone signal is one octave lower than the sound source signal, but it can be made lower than the tone signal by two octaves or more by changing the frequency of the modulation signal.

In addition to the electric piano, an electric guitar can also be used as a mechanically vibrating musical instrument, and in addition to these stringed instruments, wind instruments and percussion instruments can also be used. As described above, according to the octave conversion method of the present invention, it is possible to obtain a musical tone signal n octaves (n is a natural number) lower than the sound source signal with a tone close to a natural tone.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a musical tone generator using an embodiment of the octave conversion method according to the present invention, FIG. 2 is a circuit diagram of a specific embodiment of the envelope generating circuit portion, and FIG.
The figure is a waveform diagram of each signal. 1, 3, 5... Filter, 2... Voltage control amplifier, 4... Mixing circuit, 6...
... Rectifier circuit, 7...゜Comparator, 8...
...Envelope generation circuit.

Claims (1)

[Scope of Claims] 1. A sound source signal obtained by electrically detecting the mechanical vibration of a musical instrument and a modulation signal of a predetermined frequency are input to a voltage control amplifier, and the voltage control amplifier outputs a sound source signal that is n octaves (n) from the sound source signal.
is a natural number) In an octave conversion method for obtaining a low musical tone signal, when the sound source signal reaches a predetermined level or higher, an envelope generation circuit is operated to generate an envelope signal, and this envelope signal is added to the modulation signal. An octave conversion method that is input to the voltage controlled amplifier. 2. The octave conversion method according to claim 1, wherein the envelope signal is attenuated faster than the envelope of the sound source signal.