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Generation of noise-like tones in an electronic musical instrument
2010-02-27 00:00:00
AbstractAn electronic tone synthesizer in which a master data list of digital values representing the amplitudes of points defining the waveform of a musical tone are transferred to a digital-to-analog converter at a rate proportional to the pitch of the tone being generated. Noise is superimposed on the musical tone by means of a random binary signal generator which controls a circuit for modifying selected ones of the digital values as they are transferred from the master data list to the converter. Modification of the selected values may be by a right shift operation, a 2's complement operation, or by selective delay.ClaimsWhat is claimed is:

1. An electronic tone synthesizer for generating an audio signal having a predetermined waveform in which noise is superimposed on the audio signal, comprising: a group ofdigital words representing the relative amplitudes of equally spaced points defining the waveform of an audio signal, a digital-to-analog converter, means transferring the digital words sequentially from the generating means and applying the words inrepetitive sequence to the converter, the transferring means including means for modifying the digital value of any selected word as it is being transferred, a random signal generator for generating an output signal at random time intervals, and meansresponsive to the random output signal for momentarily activating said means for modifying a word being transferred, whereby the digital words are modified at random during transfer.

2. Apparatus of claim 1 wherein said means for modifying said digital values includes a right shift circuit for shifting the digital values of the randomly selected words numerically at least one place to the right.

3. Apparatus of claim 1 wherein said means for modifying said digital values includes a 2's complement circuit for generating the 2's complement of the digital values of the randomly selected words.

4. Apparatus of claim 1 wherein said means for modifying said digital values includes means for delaying the time of transfer at which a selected word is transferred from the generating means.

5. Apparatus of claim 2 wherein the transferring means further includes a shift register, a right shift circuit for transferring each of the digital words in sequence from the generating means to the shift register, clock means for generatingclock signals at a rate proportional to the pitch frequency of the tone being generated, said transferring means being activated by said clock signals.

6. Apparatus of claim 3 wherein the transferring means includes a shift register, a 2's complement circuit for transferring each of the digital words from the generating means to the shift register, clock means for generating clock signals at arate proportional to the pitch frequency of the tone being generated, said transferring means being activated by said clock signals.

7. In an electronic tone synthesizer in which a master data list of digital values representing the amplitude of points defining the waveform of a musical tone are transferred to a digital-to-analog converter at a rate proportional to the pitchof the tone being generated, apparatus for superimposing noise on the tone comprising: an addressable memory for storing the master data list, a shift register receiving the output of the memory, clock means for generating clock pulses at said rateproportional to the pitch of the tone being generated, the clock means shifting said register, random address generating means for selectively transferring words from any one of a plurality of locations in the master data list memory to the shiftregister with each clock pulse, and means transferring the words in the shift register to said converter to convert said words to an analog voltage whose amplitude is controlled by the digital values of said words stored in the shift register.

8. A tone synthesizer comprising source means providing a group of words representing respectively the amplitudes of equally spaced points defining the waveform of a musical tone, digital-to-analog converter, means transferring said group ofwords in timed sequence from the source means and applying the words to the converter, and a random signal generator for generating timing pulses at random time intervals, said transferring means including means responsive to the timing pulses from saidrandom signal generator for modifying the values of those digital words transferred in time coincidence with the pulses from the random signal generator.DescriptionFIELD OF THE INVENTION

This invention relates to musical tone synthesizers, and more particularly, to a noise generator for a digital tone generator.

BACKGROUND OF THE INVENTION

The generation of musical tones electronically, either by analog or digital circuits, is well known. In attempting to duplicate the sounds of conventional musical instruments it may be desirable to superimpose sounds which can only becharacterized as "noise" onto the musical tones. Such added noise may be introduced to simulate the air noise, hiss, or breathiness characteristic of wind-operated instruments, such as the organ pipes of a conventional organ, or other types of windinstruments. In prior art digital type organs tones have been created imitative to noisy wind-blown organ pipes, by using a frequency modulation technique. This has been accomplished by adding or subtracting a fixed constant to the frequency numberused to address the tone data. Alternatively, the noise has been added to the reference voltage of the analog output signal from the digital-to-analog converter to produce an amplitude modulated noise. Noiselike tones have been created in digital tonegenerators by the type which calculate musical waveshapes by computation with an algorithm that uses sets of harmonic coefficients. However, the resulting tonal effect is not easily controlled. If the harmonic coefficients are varied in a randomfashion, noise having a very wide spectrum is produced and has the effect of substantially obliterating the basic musical tone being generated.

SUMMARY OF THE INVENTION

In copending application Ser. No. 603,776, filed Aug. 11, 1975, entitled "Polyphonic Tone Synthesizer", now issued as U.S. Pat. No. 4,085,644 there is described a digital tone generator in which a master data list is calculated and stored ina main register. The master data list consists of a series of digital values representing the amplitudes of a corresponding series of points defining the waveform of one cycle (or fraction of a cycle) of a musical tone. The master data list istransferred from the main register to a Note shift register and from the Note register to a digital-to-analog converter at a rate determined by the pitch or fundamental frequency of the tone being generated. Because the ...

Electronic musical instrument with exponential keyboard and voltage controlled oscillator
2010-02-26 00:00:00
AbstractAn electronic musical instrument includes an oscillator for generating a signal at a frequency corresponding to that associated with a depressed key of the keyboard. The key selects a control voltage, from an exponential voltage divider, for controlling the frequency of a voltage controlled oscillator, which produces a frequency which is directly proportional to the control voltage and inversely proportional to a reference voltage. The reference voltage compensates for variations in the level of the supply voltage, so that the oscillator frequency is independent of the supply voltage.ClaimsWhat is claimed is:

1. An electronic musical instrument having a voltage controlled oscillator for producing a sound signal having a frequency proportional to a control voltage applied to it, akeyboard having a plurality of keys, a plurality of switches, one for each of said keys, each adapted to be operated by depression of its associated key, and a voltage divider connected with said switches for connecting a control voltage to saidoscillator which corresponds to the position of the key associated with an operated one of said switches, said voltage divider comprising a plurality of resistance elements connected in series, each of said elements having different resistance valueswhich bear an exponential relation to the resistance values of the adjacent connected resistors such that the voltage at successive junctions of said resistance elements correspond to a geometric series, said resistance elements being formed of the samematerial and being physically located in close physical juxtaposition with each other, so that all said resistors are maintained at approximately the same temperature, with approximately constant relative resistances.

2. Apparatus according to claim 1 wherein said resistance elements are formed simultaneously as portions of a single integrated thick-film circuit.

3. In an electronic musical instrument having an electrical power supply, a voltage controlled oscillator for producing a sound signal having a frequency proportional to a control voltage applied to it, a keyboard having a plurality of keys, aplurality of switches, one for each of said keys, each adapted to be operated by depression of its associated key, and connecting means connected with said switches for connecting a control voltage to said oscillator which corresponds to the position ofthe key associated with an operated one of said switches, the combination comprising a reference voltage generator connected to said electrical power supply for producing a reference voltage, and means connecting said oscillator to said reference voltagegenerator, said reference voltage generator being adapted to produce a shift in the level of said reference voltage in response to a change in the level of voltage of said electrical power supply, said shift having a magnitude and direction tending tocompensate for said change in power supply voltage level, whereby said oscillator frequency is substantially independent of said change.

4. Apparatus according to claim 3, wherein said reference voltage generator comprises an inverter having an input connected with said power supply.

5. Apparatus according to claim 4, wherein said oscillator comprises an integrator for integrating a voltage derived from said voltage divider, a comparator connected to said integrator and operative to compare an output produced by saidintegrator with said reference voltage, and means connected with said comparator and operative upon a comparison of said integrator output and said reference voltage for resetting said integrator for a subsequent cycle of integration.

6. An electronic musical instrument having a voltage controlled oscillator for producing a sound signal having a frequency proportional to a control voltage applied to it, a keyboard having a plurality of keys, a plurality of switches, one foreach of said keys, each adapted to be operated by depression of its associated key, a voltage divider connected with said switches for connecting a control voltage to said oscillator which corresponds to the position of the key associated with anoperated one of said switches, said voltage divider comprising a plurality of resistance elements connected in series, each of said elements having resistance values which bear an exponential relation to the resistance values of adjacent connectedresistors such that the voltage at successive junctions of said resistance elements correspond to a geometric series, means for supplying a selected potential across said series circuit, whereby said control voltage is dependent both on which of saidswitches is operated and on the selected potential, and selector means for selecting one of a plurality of potentials for application to said series circuit.

7. Apparatus according to claim 6, wherein said selector means comprises means for selecting one of a plurality of discrete voltage levels for application to said series circuit, said discrete voltage levels differing from each other by factorswhich are powers of two, whereby the frequency of said sound signal falls within an octave selected by said selector means.

8. Apparatus according to claim 6, including means for producing an a.c. signal, means for coupling said a.c. signal to said voltage divider, and detector means connected with said control voltage for developing a signal in response to detectionof said a.c. signal following depression of one of said keys.

9. An electronic musical instrument having a first voltage controlled oscillator for producing a sound signal having a frequency proportional to a control voltage applied to it, a keyboard having a plurality of keys, a plurality of switches, onefor each of said keys, each adapted to be operated by depression of its associated key, a voltage divider connected with said switches for connecting a control voltage to said oscillator which corresponds to the position of the key associated with anoperated one of said switches, said voltage divider comprising a plurality of resistance elements connected in series, each having resistance values which bear an exponential relation to the resistance values of adjacent connected resistors, such thatthe voltage at successive junctions of said resistance elements corresponds to a geometric series, a second voltage controlled oscillator, and tuning means for connecting said control voltage to said second oscillator, said tuning means being operativeto modify said control voltage whereby said second oscillator oscillates at a frequency which differs from the frequency of the first oscillator by a constant factor.

10. Apparatus according to claim 9, wherein said tuning means includes manually adjustable means for selecting a predetermined relationship between the frequencies of said first and second oscillators.DescriptionBACKGROUND

1. Field of the Invention

The present invention relates to electronic musical instruments, and more particularly to the class of such instruments known as synthesizers.

2. The Prior Art

Electronic music synthesizers generally include an oscillator with means for selectively controlling the frequency produced by the oscillator, so that the output of the oscillator may be caused to produce musical tones and sounds. One componentof a synthesizer is a tunable oscillator, and it is important that the oscillator remain in tune, without varying as a result of changes in temperature and other environmental conditions. If the oscillator does not inherently have the requiredstability, it must frequently be retuned, which is an inconvenience. In addition, rapid changes in tune (e.g., during warming up) are musically unsatisfactory.

In one class of synthesizers, a voltage divider is employed with several taps which are selected individually in accordance with the frequency of the signal which is desired to be produced by the oscillator. It is conventional to construct sucha voltage divider by connecting in series several components which all have the same resistance, so that an equal voltage difference is developed by each change in the position of a selected tap, connected to the junction of adjacent components. It isnecessary to use an oscillator arrangement which produces a frequency which is an exponential function of the control voltage, so that twelve successive taps produce the frequencies corresponding to the various notes of one octave of the musical scale.

Several designs for oscillators which have the required exponential function have been developed. In one such design, the oscillator is provided with a function generator for developing an exponential function in response to a linear inputvoltage, and a linear oscillator is controlled by the output of the function generator. This design has not been completely successful, because the function generator and the oscillator are both responsive to changes in the environmental condition, suchas temperature, power supply voltage level, etc., and so the required stability has not been attained.

It is, therefore, desirable to produce a system in which the aforementioned disadvantages are overcome.

SUMMARY OF THE PRESENT INVENTION

It is a principal object of the present invention to provide means for generating a variable frequency signal in response to depression of one of a plurality of keys of the keyboard, in which there is a high degree of compensation for changes inenvironmental conditions, such as changes in the ambient temperature and in the supply voltage.

This and other objects and advantages of the present invention will become manifest upon an examination of the following description and the accompanying drawings.

In one embodiment of the present invention, there is provided an electronic musical instrument having a keyboard with a plurality of keys for selecting the pitches of musical sounds to be produced, a plurality of switches individually associatedwith the keys of said keyboard, a voltage divider having a plurality of resistance elements which are exponentially related to each other and connected with the switches to produce a control voltage, the level of which is a function of the supply voltageand the operated key, means for developing a reference voltage in response to said supply voltage, whereby a fractional variation in the supply voltage produces a proportionately equal and opposite fractional variation in the reference voltage, andoscillator means connected to said control voltage and to said reference voltage for developing a signal having a frequency proportional to the control voltage and inversely proportional to the reference voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, in which:

FIG. 1 is a functional block diagram, partly in schematic circuit diagram form, comprising an illustrative embodiment of the present invention;

FIG. 2 is a schematic circuit diagram, partly in functional block diagram form, of a keyboard circuit of the apparatus of FIG. 1;

FIG. 3 is a schematic circuit diagram, partly in functional block diagram form, of an oscillator circuit employed in the musical instrument of FIG. 1; and

FIG. 4 is a functional block diagram of an alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a functional block diagram of an electronic musical instrument incorporating an illustrative embodiment of the present invention is illustrated. The system of FIG. 1 includes a keyboard 10 having a plurality of switches12 associated therewith in conventional fashion. When each key of the keyboard 10 is depressed, one of the switches 12 is closed. An exponential voltage divider 14 is associated with the switches 12, and one of a plurality of leads 4 connected to thetaps of the voltage divider 14 is connected by an individual switch 12 to a sample and hold unit 5, via a line 13. The unit 5 manifests, on an output line 6, the voltage present on the line 13, which is dependent upon the operated switch 12. The sampleand hold unit 5 has a triggering unit 7 which is connected with the switches 12 and which is responsive to closing thereof for activating the sample and hold unit 5.

The exponential voltage divider 14 is made up of a series of resistors, as shown in FIG. 2, the resistance values of which are related in a geometric series, so that the value of the voltage at the taps of the voltage divider (between the pairsof adjacent resistors) has an exponential relationship, i.e. the voltages at the taps are approximately directly proportional to the frequencies of the notes of the musical scale.

A high frequency generator 8 is also associated with the switches 12. The generator 8 produces a high fr...

Rotary valve for a musical instrument
2010-02-25 00:00:00
AbstractA rotary valve for selectively inserting and removing a slide loop from the sound path of a musical instrument is disclosed. The valve includes a cylindrical rotor housed in a cylindrical casing coupled to the instrument's lead pipe, main bore and slide loop leading and trailing ends. The rotor has two passages extending through it. The first passage is generally "Y" shaped with two leading ends and a trailing end, while the second passage is generally straight having a leading end and a trailing end. In a first valve position, the first leading end and the trailing end of the "Y" shaped rotor passage coaxially align with the instrument's lead pipe and main bore, respectively, providing an air pathway excluding the additional slide loop. In a second valve position, the second leading end and the trailing end of the "Y" shaped passage coaxially align with the instrument's lead pipe and slide loop leading end, respectively, while the leading end and trailing end of the straight rotor passage coaxially align with the instrument's slide loop trailing end and main bore, respectively, to provide an air pathway including the additional slide loop. The present rotor design eliminates undesirable noises during rotor operation common to prior rotors while not adversely affecting the integrity and quality of the air column during play.Claims

What is claimed:

1. A rotary valve for musical instruments having a lead pipe, a main bore pipe leading to a horn bell and an alternate slide loop with a leading end and a trailing end, the valve comprising:

a cylindrical casing having a cylindrical sidewall, a top end, a bottom end and an inner circumferential surface, the casing being formed to include radially spaced apart first, second, third and fourth apertures extending through the cylindrical sidewall, the lead pipe, slide loop leading end, slide loop trailing end, and main bore pipes being coupled to the casing in communication with the first, second, third and fourth apertures, respectively; and

a cylindrical rotor having an outer circumferential surface, the rotor being coaxially mounted in the casing for rotation about a rotor axis between predetermined unswitched and switched positions such that the outer rotor surface maintains sealing contact with the casing inner circumferential surface, the rotor being formed to include a first generally "Y" shaped passage having first and second leading ends and a trailing end, and a second passage having a leading end and a trailing end, the first and second passages being aligned through the rotor so that when the rotor is in the unswitched position, the first leading end and the trailing end of the first passage are coaxially aligned with and in communication with the first and fourth casing apertures respectively while the second leading end of the first passage is in sealing contact with the casing inner circumferential surface, and when the rotor is in the switched position, the second leading end and the trailing end of the first passage are coaxially aligned with and in communication with the first and second casing apertures respectively while the second leading end of the first passage is in sealing contact with the casing inner circumferential surface, and the leading and trailing ends of the second rotor passage are coaxially aligned with and in communication with the third and fourth casing apertures respectively.

2. The rotary valve of claim 1, wherein the first and second leading ends of the first rotor passage are aligned at an acute angle relative to one another.

3. The rotary valve of claim 1, wherein the first leading end and the trailing end of the first rotor passage coaxial with one another.

4. The rotary valve of claim 3, wherein the first and second leading ends of the first rotor passage are aligned at an acute angle relative to one another.

5. The rotary valve of claim 1, wherein the second leading end and the trailing end of the first rotor passage are substantially coaxial with one another.

6. The rotary valve of claim 1, wherein the second passage has a generally straight shape.

7. The rotary valve of claim 1, wherein the second passage has an arcuate shape.

8. A rotary valve for a musical instrument which includes a lead pipe coupled to a mouthpiece, a main bore pipe leading to a horn bell, and an alternate slide loop having a leading end and a trailing end, the valve comprising:

a casing configured to be coupled to the musical instrument; and

a rotor configured to be mounted in the casing for rotation about a rotor axis between predetermined unswitched and switched positions, the rotor being formed to include a first generally "Y" shaped passage having first and second leading ends and a trailing end, and a second passage having a leading end and a trailing end, the first passage being configured to direct air from the lead pipe, through the first leading end of the "Y" shaped passage, out the trailing end, and through the main bore pipe leading to a horn bell when the rotor is in its unswitched position, and the first and second passages also being configured to direct air from the lead pipe, through the second leading end of the "Y" shaped passage, out the trailing end, through the alternate slide loop, through the second passage, and through the main bore pipe leading to a horn bell when the rotor is in its switched position.

9. The rotary valve of claim 8, wherein the first and second leading ends of the first rotor passage are aligned at an acute angle relative to one another.

10. The rotary valve of claim 8, wherein the first leading end and the trailing end of the first rotor passage are substantially coaxial with one another.

11. The rotary valve of claim 10, wherein the first and second leading ends of the first rotor passage are aligned at an acute angle relative to one another.

12. The rotary valve of claim 8, wherein the second leading end and the trailing end of the first rotor passage are substantially coaxial with one another.

13. The rotary valve of claim 8, wherein the second passage has a generally straight shape.

14. The rotary valve of claim 8, wherein the second passage has an arcuate shape.Description

This invention relates to a rotary fluid flow valve and more particularly to a rotary air valve for musical instruments.

One recognized method of changing tones in a musical wind instrument, particularly a brass instrument, is to change the length of the path an air column travels through the instrument. One method of accomplishing this is to provide the instrument with alternate loops of tubing of different lengths connected by one or more valves. As a valve is switched between alternate set positions, the air column is diverted through alternative desired combinations of loops resulting in different path lengths and thus different tones.

Rotary valves have long been used for musical instruments and are highly regarded for their quick action and relative simplicity of structure as compared to piston-type valves. Rotary valves have made strides in reducing overtones in the sound of the instrument caused by sound waves partially reflecting off the inside walls of the air passages as the air column travels through bends. Such partial reflection reduces the energy of the fundamental sound wave and produces undesirable overtones. Current rotary valves such as the Selmer-K valve and the Thayer valve reduce overtones by minimizing bends in the air passages through the valve and by providing air passage cross sections that are as congruent as possible a...