US3538806A - Tone processing system - Google Patents

Description

United States Patent [72] Inventor David A. Bungei' 3,391,240 7/1968 Uetrecht 84/l.l9X Cincinnati, Ohio 3,429,976 2/1969 Tomcik 84/ 1.12 [211 App]. No. 712,117 Primar "l I y Exammer- Herman k. Saalbach g fs g f r Assistant ExaminerT. Vezeau a Attorneys-W. H. Breunig and Hurvitz, Rose & Greene [73] Assignee D. H. Baldwin Company Cincinnati, Ohio a corporation of ohm ABSTRACT: A tone derived from a conventional musical in strument, such as a clarinet, is converted to a square wave signal having the same fundamental frequency as the funda- [54] TONE PROCESSING SYSTEM mental frequency of the tone. The square wave signal frequen- 7 Claims, 2 Drawing Figs cy is divided by two, and again by two, and is also multiplied by two-thirds, to provide three waves, each of which may be [52] US. Cl 84/1-12, processed by tone color filters to have a variety f musical 84/121 84/122 sounds, as the sounds of the oboe, tuba, flute, etc. The original [51] IIILCI Gloh 3/00, tone is detected to provide a DC gain control signal which Gloh l/oztcloh 1/06 controls the conductivity of a diode gate through which the [50] Field ofSeai'ch 84/l.0l, Processed tone passes Conversion to a Square wave Signal is accomplished by oppositely poled diode peak detectors, each [56] References Cited including a diode and a'capacitor in series with the diode, the capacitors having a common resistive path to ground, so that UNITED STATES PATENTS charging of one capacitor is always accompanied by discharg- 2,989,886 /1 1 Mark witZ 84/l.19 ing of the other. The conversion system is thus capable of 3,213,130 10/1965 C y el /1-1 1 responding to alternate half cycles of complex waves, over 21 3,256,381 6/1966 Cookerly et a]., 84/].27 very wide range of frequencies, say from about 50c.p.s. t0 ""Llfifi ll/l967 Diidek et al. 307/235X about 5,000c.p.s

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INVENTOR v DNHD A. BUNGER ATTORNEYS TONE PROCESSING SYSTEM BACKGROUND OF THE INVENTION The general procedure of processing tones provided by conventional musical instruments is old. Reference is made to US. Pat. Nos. as follows: Earp, 2,561,349; White, 3,006,228; Hanert, 2,514,490; Cookerly et al., 3,213,180.

The prior art systems lack a suitable device for assuring that the fundamental of a complex musical tone will, for all frequencies and wave shapes, assume reliable control of the system, keeping in mind that wave shapes of tones produced by musical instruments, such asthe clarinet, differ radically among themselves in respect to wave shapes. In the past it has been usual to roll off frequencies of the tone, so that the fundamental, if initially at least as great as any harmonic of the tone, will assume control of the system. However, many musical tones have harmonics which far exceed the fundamental in amplitude. In these circumstances the output of the system tends to shift at random in the course of playing a single note. It is to this problem that the present system primarily addresses itself.

SUMMARY OF THE INVENTION The output of an acousto-electrical transducer, controlled by a musical instrument, is applied to a push-pull diode peak detector which generates square waves at the frequency of the fundamental of the output of the transducer, for a wide variety of wave shapes and for a wide range of frequencies. The square wave is divided by two and again by two, and also is multiplied by two-thirds, thirds, followed by division by three, and multiplied by two.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a system according to the invention; and

FIG. 2 is a schematic circuit diagram of a system according to FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an audio input signal, which may be derived from an acousto-electric transducer operatively associated with a horn, clarinet, guitar, or the like, is applied to a diode wave shaper 11, which converts the wave to one resembling a square wave having the same fundamental frequency as does the audio input signal. The output of the diode wave shaper drives a transistor flip-flop 12, which provides a square wave at the fundamental frequency, but of level amplitude regardless of the amplitude of the audio signal. The output of flip-flop 12 drives two cascaded divide-by-two circuits, 13 and 14, a multiply by two circuit and a multiply by circuit, each of which supplies complex signal to an array TC of tone color filters, selectable by operation of tabs, not illustrated. The output of array TC proceeds to a diode gate 16 which controls signal level in response to a DC control voltage applied via control lead 17, and which leads to an audio amplifier 18. The latter drives a loudspeaker 19. It follows that any complex audio tone, regardless of its wave shape, and of fundamental frequency F, can produce square waves of fundamental frequency F, F/2, 2F, F and another of fundamental frequency F/4. These can be processed by tone color filters TC to have the tone colors of various instruments, for example, clarinet, oboe, flute, tuba, saxaphone, dulciana.

The output of transducer 10 is detected in smoothing detector 20, which provides DC gain control signal on lead 17, so that the level of sound emitted by loudspeaker 19 will follow that of transducer 10, and therefore of the level provided by the instrument with which the transducer is associated.

To the outputs of flip-flop 12 is connected a diode frequency doubler 21. The latter derives a divide-by-three circuit 22, the output of which in turn is applied to the array TC of tone color filters. The frequency F as provided by flip-flop 12, the outputs of divide-by-two circuits 13, 14, the output of multiplier 21, and the output of divide-by-three circuit are applied via separate leads to tone color filters TC.

In FIG. 2, the output of transducer 10 is applied via coupling capacitor 30 and base current limiting resistance 31 to the base of NPN transistor T having a grounded emitter. The collector of T is loaded by resistance 32, and the resistances 33, 34 serve to bias the base. Capacitor 35 provides frequency selective feedback to accentuate response as an inverse function of frequency, i.e. it provides roll off, which accentuates the fundamental of a complex wave at the expense of higher partials.

The amplified audio signal-appearing at point 36 is superposed on a DC voltage of about l2.V representing DC supply voltage of 22.V less the DC voltage drop in resistance 32. To the point 36 are directly connected the base of diode D and the anode of diode D A DC path exists through diodes D,, D, from supply leads S through resistances 40, 41, respectively, nearly one-half of the available voltage being dropped in resistance 40. This implies that the anode of D is at about l2.V, and both diodes are biased slightly conductive. When the AC signal goes positive it charges capacitor 43 approximately to its own peak level, and this charge is retained during a half a cycle of input wave so that if the positive half cycle is quite complex, as is usually the case, any dips of level in the course of the positive half cycle do not affect the output level at the base of T Similarly when the signal goes negative with respect to the normal DC level of point 36 diode D charges capacitor 44, which back-biases the diode D, and prevents transient drops in level from generating reverse flows through capacitor 44. Charging of capacitor 44 induces discharge capacitor 43, and vice versa. Since transfer of charging function occurs as the input signal wave passes through zero level, the system can respond to AC waves over a wide range of frequencies, say 50 c.p.s. to 5,000 c.p.s. The double diode, double capacitor detection system may well be denominated a push-pull peak detector, since it responds to alternate polarities of a wave to provide a clipped AC output which approximates a square wave. The closeness of the approximation depends, however, on the complexity of the input wave form, Le. the relative amplitudes and phases of its component partials.

D,, 44 is a peak detector, and D 43 is a peak detector, for negative and positive signals, respectively, capacitors 43, 44 being in series with respect to diodes D D and the circuit tends to produce a square wave at the peaks of the input wave form, changing state as the input signal reverses polarity. Current through load resistance 53 is then an AC signal with respect to the DC bias for transistor T established by resistances 51, 52, 53. Since the load and bias circuits for T and T are identical, the DC level at point 54 is nearly the same as the DC level at point 36. T saturates on sufficiently large signals, its output having values extending to 0 and 22.V as the comprising two cross-connected NPN transistors T and T in a configuration which is conventional and hence is not further described. The collector of T its emitter being grounded, is AC coupled via capacitor 60 to the cathode of a grounding diode D and to the anode of a series diode D the cathode of which is grounded through resistance 63. The capacitor 60 and resistance 63 convert the DC variations of voltage at the collector T to short pulses, of which only the positive halves pass to junction 61. A similar arrangement pertaining to the collector of T involves capacitor 62 and diodes D and D Diodes D and D together then pass each oscillation of FF-l, and the pulse frequency at junction 61 is double that supplied by T Essentially 60, 63 is a differentiator which is rendered inoperative to negatively going pulses by D D and 62, 63 is a further differentiator.

The pulses available at junction 61 are applied to a divideby-three circuit 22, in the form of a ring counter of conventional configuration, via a drive amplifier 66 having an NPN transistor T Divide-by-three circuit 22 employs three cascaded NPN transistors T T T The output of amplifier 66 is applied jointly to the collectors of the transistors T T T through 2.2 K resistors 70, 71, 72, these being connected back to DC supply via resistance 73 (820 9). Each collector is connected back to the base of the preceding transistor, i.e. T to T T to T and T to T and forward via wave shaping circuits 74, 75, 76, respectively, i.e. T to T,, T-, to T and T to T,. The configuration is well known, and since circuit values are provided a detailed description of operational mode is dispensed with.

The output of divide-by-three circuit 65 appears directly at the collector of T and is applied via a voltage divider 80 and lead 81 to an array of tone color filters TC, selective by tab operated switches (not shown) in a manner widely employed in electronic organs. The output of the array of tone color filters TC appears across resistance 82.

The output of FF-l is applied to cascaded flip-flops 13 (FF- 2) and 14 (FF-3), arranged to operate as frequency dividers. These, and flip-flop 12, individually apply their outputs via leads 100, 83 and 84 to the array of tone color filters TC. lnterposed between the leads 100, 83 and 84 and the filters TC are adjustable voltage dividers 101, 85 and 86, respectively, which serve as volume adjusters. A further adjustable voltage divider 103, fed by lead 102 connected to the collector of transistor 66 is also provided and leads to tone color filters TC. At the input of the color filters TC can appear one or more of five signals, each of which bears a frequency relation to the frequency of the output of transducer 10. If we assume that the transducer provides a complex signal having a fundamental frequency F, the outputs at leads 100, 81, 83, 84, 102 are square waves of frequencies F, 2 F/3, F/2, F/4, 2F, respectively, and any one or more of these may be selected by tab switches (not shown).

The tones provided are, however, of preset amplitudes, which are not related to the level at which the instrument which energizes transducer is being played, in absence of the following provision. To control amplitude according to the level called for by transducer 10, the direct output of transducer 10 is amplified in amplifier 20, comprising transistor T and rectified by diodes D D of detector 20, of which D shunts negative half cycles to ground and D passes positive half cycles. A long time constant load circuit 91 for D is connected between the cathode of D and ground, so that at junction 92 appears a DC voltage having a value nearly proportional to the peak value of the output of transducer 10. Junction 92 is the control point of a diode gate 16 composed of back-to-back diodes D D through which passes in series the signal across resistance 82. Diode gate 16 is nonconductive in absence of control voltage applied to control point 92, but becomes more conductive as control voltage increases. The signal passed by gate 16 passes to a voltage amplifier 18, including an NPN transistor T and the latter drives in cascade a power amplifier 18a and loudspeaker 19.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variation of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

Iclaim:

1. In a system for processing the acoustic tonal output of a nonelectric musical instrument, wherein:

said output is a complex wave;

a transducer for coupling to said instrument and converting said acoustic tonal output to an electrical signal having a complex wave form;

a push-pull peak rectifier circuit connected to said transducer;

said push-pull peak rectifier including a junction to which is applied said electrical signal;

a first diode having its cathode connected to said junction;

a first capacitor connected to the anode of saiddiode; a load resistance connected in cascade with said first capacitor;

a second diode having its anode connected to said junction;

a second capacitor connected to the cathode of said second diode;

means connecting said second capacitor in cascade with said load resistance; and i a frequency divider coupled to the output of said push-pull rectifier circuit.

2. The combination according to claim 1 wherein is provided a transistor circuit responsive to the voltage across said load resistance and arranged to become alternately nonconductive and saturated as the voltage across said load resistance changes algebraic sign.

3. The combination according to claim 2 wherein is provided a flip-flop having a signal control terminal responsive to said transistor clipping circuit.

4. The combination according to claim 3, wherein is provided:

diode differentiators responsive to all state transitions of said flip-flop to provide pulses at twice the frequency of operation of said flip-flop a divide-by-three counter circuit responsive to said pulses;

a tone color filter array responsive to the output of said divide-by-three circuit; and

a loudspeaker coupled to the output of said tone color filter array.

5. An audio gain control'circuit, including:

a source of complex audio tone signals of variable mean amplitudes;

a diode amplitude detector responsive to said tone signals for providing a DC signal constantly proportional in amplitude to said mean amplitude;

a diode gate including back-to-back connected diodes with the connection of said diodes forming a control point;

means responsive to said complex audio tone signals for generating square wave signals of always the same amplitude regardless of the amplitude of said audio tone signals but of a fundamental frequency obtained by a simple frequency division from the fundamental frequency of said complex audio tone signals;

means for musically modifying the frequency spectrum of said square wave signals to provide musical electrical signals;

means applying said musical electrical signals in cascade with said gate through said diodes; and

means for applying said DC signal to said control point, said gate being arranged to be normally nonconductive in absence of said DC signals at said control point.

6. The control circuit of claim 5 wherein said means responsive to said complex audio tone signals includes a push-pull rectifier circuit connected to said source of complex audio tone signal.

7. The control circuit of claim 6 wherein said pushpull rectifier includes:

a first peak detector responsive only to the positive portions of said complex audio waves;

a second peak detector responsive only to the negative portions of said complex audio waves; and

a common resistive load circuit for said first and second peak detectors.

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