Musical Tone-forming Circuitry Including Filter And Random Noise Modulation

Abstract

A whistle or grass reed sound is simulated by an electronic musical circuitry comprising a portamento-type oscillator, a tone coloring filter for providing a tone signal having predetermined harmonics as well as a fundamental, a noise generator, a low-pass filter for deriving frequency components below 30 Hz from a noise signal output of the noise generator, and a modulator for amplitude modulating the tone signal from the tone coloring filter with the noise signal components of less than 30 Hz from the low-pass filter.

Description

BACKGROUND OF THE INVENTION

This invention relates to a tone-forming device for electronic musical instruments, and more particularly to a device capable of readily producing musical tones of special timbers resembling those of whistles or grass reeds which are usually difficult to produce by the conventional electronic musical instruments.

The conventional electronic musical instrument is usually so constructed as to produce various kinds of musical tones, e.g., musical tones similar to those of a flute containing a relatively small quantity of high frequency components and musical tones similar to those of a reed instrument containing a relatively large quantity of high frequency components, by passing signals from tone generators through various tone coloring filters, whereby the desired musical signals having the desired tone colors are formed by selectively combining a signal of the fundamental frequency with different types of overtones in various level ratios.

With an electronic musical instrument utilizing the above-described method of forming musical tones it is easy to produce musical tones similar to those of ordinary reed or wind instruments which have relatively stable tone feelings but very difficult to produce musical tones having relatively unstable tone feelings such as those of whistles and grass reeds. Thus, it is highly desirable to obtain electronic musical instruments that can produce musical tones having relatively unstable tone feelings.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a tone-forming device for electronic musical instruments capable of readily producing musical tones having relatively unstable tone feelings resembling those of whistles and grass reeds.

According to this invention, the tone source signals containing the fundamental frequency and various overtones are subjected to balanced modulation or amplitude modulation by a random signal containing frequency components of less than about 30 Hz.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of one embodiment of a tone-forming device for electronic musical instruments embodying this invention;

FIGS. 2A, 2B show preferred circuit arrangements of various circuits components shown in FIG. 1;

FIGS. 3A and 3B show the waveforms of typical modulated outputs produced by the modulation circuit shown in FIG. 1; and

FIG. 4 shows an amplitude modulation circuit utilizing an FET that can be substituted for the balanced modulation circuit shown in FIG. 2B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic block diagram of one embodiment of this invention, wherein tone signals are derived from a tone generator 11, which is used as the tone source of a conventional electronic musical instrument including a plurality of oscillators or preferably a portamento oscillator constructed in a manner to be described later. Tone signals from the tone generator 11 are passed through a tone coloring filter 12 to be converted into musical signals having desired tones similar to those of flute or reed instruments (oboe, bassoon, etc.), and the converted signals are supplied to a balanced modulator (or an amplitude modulator) 13 to be described hereinafter.

A random modulation signal is also supplied to the balanced modulator (or amplitude modulator) 13 from a source of random signal 14 comprising a white noise signal generator 15 (the construction thereof will be described later in detail) and a low-pass filter 16 which passes only frequency components of less than, for example, 30 Hz. out of the white noise signals generated by the white noise signal generator 15.

Thus, the balanced modulator (or amplitude modulator) 13 provides modulated musical signals resembling the musical signal of whistles or grass reeds having relatively unstable tone feelings which have been difficult to produce by conventional electronic musical instruments. The musical signals thus modulated are provided by suitable modulating musical signals obtained from the tone generator 11 through tone coloring filter 12 and having relatively stable tone feelings resembling those of flute or reed instruments with random modulation signals having frequency components of less than 30 Hz. which are generated by the white noise signal generator 15 and passed through low-pass filter 16. Output musical signals from the balanced modulator (or amplitude modulator) 13 are amplified, if desired, by an amplifier 17 and are then transduced by a loudspeaker 18 into the desired musical sounds.

The musical sounds of whistles or grass reeds are characterized in that their fundamental frequency generally ranges from 500 Hz. to 4 kHz., their tone feelings are unstable, their musical pitch varies continuously and their amplitude varies irregularly with a maximum degree of modulation amounting to 30 to 50 percent. The waveform of the whistle is substantially of a sine wave type containing small quantity of higher harmonics and resembling that of flutes, whereas the waveform of the grass reed contains a relatively large quantity of higher harmonics and resembling that of reed instruments.

When the tone generator 11 is so constructed as to selectively produce tone signals having a fundamental frequency ranging from 500 Hz. to 4 kHz., and when the tone coloring filter 12 is so designed as to suitably select the desired percentage of the high frequency contents of the tone signal, it is possible to produce tone signals resembling those of flute and reed instruments. It is also preferable to set the degree of modulation by the balanced modulator (or amplitude modulator) 13 at a range of from 30 to 50 percent. Further, it is preferable to form the tone generator 11 from a portamento oscillator, as the musical pitch of the tones selectively generated thereby can vary continuously. The tone signals produced through the tone coloring filter 12 and resembling those of flute or reed instruments are subjected to balanced modulation (or amplitude modulation) 13 and are modulated with random modulation signals generated by the white noise signal generator 15 and passed through the low-pass filter 16 which acts to selectively pass only frequency components of less than about 30 Hz., with the result that the amplitude of the modulated musical signal outputs varies irregularly.

Thus the tone-forming device for electronic musical instruments can readily produce tone signals resembling those of whistles and grass reeds having relatively unstable tone feelings which heretofore have been difficult to produce by conventional electrical instruments, so that said device has a broader field of application.

Turning now to FIGS. 2A and 2B illustrating the detailed construction of the circuit shown in FIG. 1, the portamento oscillator serving as a tone generator 11 is a modified form of a Wien's bridge oscillator which comprises a plurality of oscillation frequency determining circuits 111a, 111b, 111c and 111d including parallel circuits of resistors R11a, R11b, R11c, R11d and capacitors C11a, C11b, C11c, C11d and serial circuits connected therewith and including resistors R21a, R21b, R21c, R21d and capacitors C21a, C21b, C21c and C21d. Junctures between said parallel circuits and serial circuits involved in the respective oscillation frequency determining circuits are connected to the corresponding taps of an elongated bar resistor 113a respectively through emitter follower circuits 112a, 112b, 112c and 112d. The resistor 113a is associated with the opposite electrically conductive flexible contact 113b. These elements are normally set apart from each other and constitute a kind of potentiometer serving as a fingerboard to be manipulated in playing music. With this fingerboard, the oscillation frequency is determined by the position at which the contact 113b is depressed for contact with the resistor 113a. The signal having an oscillation frequency determined by the manner in which the fingerboard is operated is supplied to a phase dividing amplifier 114 which produces two outputs in the opposite phases. The two outputs are supplied across the aforementioned frequency determining circuits. Thus is formed an oscillation loop which includes the oscillation frequency determining circuits 111a to 111d, the emitter follower circuits 112a to 112d, the fingerboard 113, and the amplifier 114. This oscillation loop is normally open but is closed by the selective operation of any point of the fingerboard 113 to produce a tone signal having the frequency determined by the position of the particular point depressed. Oscillation frequencies fa, fb, fc and fd of the oscillation frequency determining circuits 111a to 111d are given by

fa=1 / 2.pi. C11a.sup.. C21a.sup.. R11a.sup.. R21a

fb=1/2.pi. C11b.sup.. C21b.sup.. R11b.sup.. R21b

fc=1/2.pi. C11c.sup.. C21c.sup.. R11c.sup.. R21c and

fd=1/2.pi. C11d.sup.. C21d.sup.. R11d.sup.. R21d

With this arrangement, it is possible to easily provide the portamento effect by continuously sliding the finger tip over the fingerboard. The tone signals produced by the portamento oscillator 11 substantially has a sine waveform containing a relatively small quantity of higher harmonics, and resembling the waveform of musical signals produced by flutes. Accordingly, in this case, the tone coloring filter 12 includes a clip circuit 121 and a tone coloring filter circuit 122 for obtaining the tones of a reed instrument. Either of the whistle and grass reed tones is selectively produced by means of a switch SW.

Since the signals produced by the portamento oscillator 11 substantially have a since wave containing relatively small quantity of high harmonics, it is only required to cause these signals to pass directly to terminal X in order to form tone signals resembling the tones of flutes, whereas, to form tone signals resembling those of reed instruments, it is necessary to cause the signals to pass first through the clip circuit 121 so as to increase its percentage of higher harmonic content and then through the tone coloring filter circuit 122.

The white noise signal generator 15 in the random signal source 14 comprises a noise source 15a consisting of a transistor TR with a negative bias applied across its base and emitter electrodes (or a conventional diode may be used) to utilize the breakdown characteristic of the transistor and an amplifier 15b for amplifying the noise signal. The white noise signal thus produced is passed through a .pi. type low-pass filter 16 comprising a choke coil CH and two capacitors C1 and C2 so designed as to allow only frequency components of less than about 30 Hz. to pass therethrough.

The balanced modulator 13 comprises a signal input transformer T1 connected to receive tone signals resembling those of flute or reed instruments and supplied through the tone coloring filter 12, an input transformer T2 connected to receive random signals supplied from the random signal generator 14 and having frequency components of less than 30 Hz., and an output transformer T3 for deriving modulated signals, said transformers T1, T2 and T3 including magnetically coupled primary windings T1.sub.p, T2.sub.p and T3.sub.p and secondary windings T1.sub.s, T2.sub.s and T3.sub.s, respectively.

Between the secondary winding T2.sub.s of the modulating signal input transformer T2 and the primary winding T3.sub.p of the output transformer T3 is connected a diode rectifier bridge circuit 131 including four diodes D1, D2, D3 and D4 which are connected to each other with the indicated polarities. The opposite terminals of the secondary winding T1.sub.s of the signal input transformer T1 are connected to the intermediate terminal CT on the secondary winding T2.sub.s of the modulating signal input transformer T2 and the intermediate terminal CT' on the primary winding T3.sub.p of the output transformer T3, respectively. Thus, the output transformer T3 of the balanced modulator 13 provides a modulated musical signal V having relatively unstable tone feelings like the sounds of whistles or grass reeds, said modulated musical signal being obtained by subjecting the source signal Vc produced by the portamento oscillator 11 and passed through the tone coloring filter 12 and having tones resembling those of flutes or reeds to balanced modulation by a random modulation signal Vm produced by the white noise signal generator 15 and passed through the low-pass filter 16 and having frequency components of less than about 30 Hz., as shown in FIG. 3A. The resultant output is reproduced by a loudspeaker 18 after being amplified by the amplifier 17, if desired.

FIG. 4 shows the circuit arrangement of an amplitude modulator 130 having equivalent sound effects to those offered by the balanced modulator 13 and may be substituted therefor. As shown, a field effect transistor (FET) is used with its gate terminal G grounded through a resistor R3. The source signal Vc from the tone coloring filter 12 is supplied to the source terminal S (or drain terminal D instead) of the FET, whereas the random modulating signal Vm having frequency components of less than about 30 Hz. is conducted to the gate terminal G through the low-pass filter 16, whereby an amplitude modulated musical signal Vo, (see FIG. 3B), having relatively unstable tone feeldings like the tones of a whistle or grass reed is drawn out through the other drain terminal D (or source terminal S instead).

As described hereinabove, the invention provides a tone-forming device for electronic musical instruments wherein the selective operation of the fingerboard of the electronic musical instruments enables musical signals of relatively unstable tone feelings similar to those of whistles and grass reeds, to be readily produced though the conventional musical instruments failed to generate such musical tone signals. Accordingly, the invention has a broader field of application.

Claims

I claim:

1. A musical tone forming circuit comprising:

a tone generator including portamento-type oscillator means for producing a tone signal having gradually variable frequency:

a tone coloring filter coupled to the output of said tone generator for producing a tone signal having a predetermined harmonics and a fundamental frequency:

a white noise signal generator;

a low-pass filter for deriving frequency components below 30 Hz. out of a noise signal from said white noise signal generator; and

an amplitude modulator for amplitude modulating a tone signal from said tone coloring filter with a noise signal from said low-pass filter.

2. The tone-forming circuit according to claim 1 wherein said white noise signal generator comprises a negatively biased transistor circuit, the breakdown characteristic of said transistor being utilized in generating said white noise signals.

3. The tone-forming circuit according to claim 1 where said amplitude modulator comprises a balanced modulation circuit including an input transformer for supplying tone signals obtained from said tone coloring filter, an input transformer for supplying the modulating signals obtained from said low-pass filter and an output transformer for taking out output signals obtained by modulating said tone signals with said modulating signals.

4. The tone-forming circuit according to claim 1 wherein said amplitude modulator comprises a field effect transistor having its gate terminal grounded through a resistor, one of its source and drain terminals being connected to receive said tone signals from said tone coloring filter, said gate terminal being connected to receive the modulating signal from said low-pass filter and the other source or drain terminal being connected to couple the modulated signals to an output.

5. The tone-forming circuit according to claim 1 wherein the tone signal from said tone coloring filter has a flute voice tone color.

6. The tone-forming circuit according to claim 1 wherein the tone signal from said tone coloring filter has a reed voice tone color.