US3604829A

US3604829A - A dynamic voicing filter for an electronic organ

Info

Publication number: US3604829A
Application number: US1918*[A
Authority: US
Inventors: David A Bunger
Original assignee: DH Baldwin Co
Current assignee: BPO ACQUISITION CORP; Baldwin Piano and Organ Co; DH Baldwin Co
Priority date: 1969-12-31
Filing date: 1969-12-31
Publication date: 1971-09-14
Anticipated expiration: 1988-09-14

Abstract

An electric organ having conventional voicing circuits is also supplied with an auxiliary dynamic voicing filter, controlled by the expression pedal of the organ. The voicing filter is an active RC filter, having a feedback loop of controllable gain, that gain determining the peak frequency of the filter. A diode gate in the feedback loop is controlled by a control voltage established as a function of position of the expression pedal of the organ.

Description

United States Patent inventor David A. Bunger Cincinnati, Ohio Appl. No. 1.918 Filed Dec. 31, 1969 Division of Ser. No. 723,685, Apr. 28, 1968 Pat. No. 3,519,720 Patented Sept. 14, 1971 Assignee D. H. Baldwin Company Cincinnati, Ohio A DYNAMIC VOICING FILTER FOR AN ELECTRONIC ORGAN 14 Claims, 3 Drawing Figs.

US. Cl 84/l.l9, 84/DIG. 9, 84/D1G. 10

Int. Cl G10h 1/02 Field of Search 84/1 .01

1.l1,1.12,1.19,1.2,1.21,1.22,l.24,DIG.9, DlG. 10; 330/31 [56] References Cited UNITED STATES PATENTS 2,647,173 7/1953 Beurtheret 84/D1G. 10 2,568,797 9/1951 Eland 84/D1G. 10 3,166,622 1/1965 Neustadt 84/].01 3,255,296 6/1966 Peterson 8411.24 3,316,341 4/1967 Peterson 84/1 .24 3,486,126 12/1969 Chin et a1. 330/31 X Primary Examiner-Milton O. Hirshfield Assistant Examiner-Stanley .1. Witkowski Attorneys-W. H. Breunig and Hurvitz, Rose & Greene ABSTRACT: An electric organ having conventional voicing circuits is also supplied with an auxiliary dynamic voicing filter, controlled by the expression pedal of the organ. The v0- icing filter is an active RC filter, having a feedback loop of controllable gain, that gain determining the peak frequency of the filter. A diode gate in the feedback loop is controlled by a control voltage established as a function of position of the expression pedal of the organ.

TAB 51D.

were" PATENTEB sen 4 new SHEET 1 [IF 2 Enw 205mm xm XQOBPNZ xuamcwwu v INVENTOR DAVID A BUNGER ATTORNEYS A DYNAMIC VOICING FILTER FOR AN ELECTRONIC ORGAN This application is a division of my application, Ser. No. 723,685, filed Apr. 28, 1968, now U.S. Pat. No. 3,519,720 and entitled Organ Having Dynamically Variable Timbre with Transistorized Player Controlled Dynamic Filter."

BACKGROUND OF THE INVENTION Prior U.S. patents relating to the subject of this invention are: Peterson, No. 3,255,296; Peterson, No. 3,316,341; and Neustadt, No. 3,166,622.

These patents involve dynamic modification of the output of tone generators of an electric organ. The present invention involves use of an active tunable RC filter of novel configuration, as a device for dynamically modulating the timber of a tone, but in addition involves the use of the in any event available expression pedal of an organ to control timber modulation, while that pedal remains available to the organ for expression control. Thereby the total number of controls which the player is called on to manipulate, in practicing the present invention, is not increased over the number required in the conventional organ, yet the total number of musical effects available to the instrument being played is increased.

SUMMARY OF THE INVENTION An electric organ conventionally includes a tone generator having discrete complex tone sources which can be selectively called forth by key switches. The complex tones, i.e. tones containing many partials, are passed through voicing filters which are selectively placed in circuit by voicing tabs. The voicing filters determine the relative amplitudes of the partials, for each tone, which are passed on to amplifiers and eventually to loudspeakers. Expression is the term employed to indicate loudness of the radiated acoustic sound, and in the conventional organ expression is controlled by a foot pedal actuated by the right foot of the player.

According to the present invention, a dynamic voicing filter is-provided which is additional to and connected in parallel with the usual voicing filter and which can be selectively operatively connected in the system at will, either in place of or in addition to the usual voicing filters. The peaking frequency of the dynamic voicing filter is a function of the position of the expression pedal. The dynamic voicing filter per se represents circuitry and principles of operation which are novel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph depicting various available response curves of a variable-timber-control filter, employed in the system of the invention;

FIG. 2 is a block diagram of a system of the invention: and FIG. 3 is a schematic circuit diagram of a dynamic filter of the system of FIG. 2, and of controls for the dynamic filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, is a signal generator which contains a signal source for each of the array of complex tones required in an electronic organ. The separate tones are called forth by closing key switches'll, as by keys'or pedals (not shown) in the process of playing the organ. The tones called for by the key switches 11 are collected on a bus 12, which leads to conventional organ voicing filters 13. The latter are conventionally selected by voicing tabs, not separately shown. The outputs of the voicing filter or filters selected by the voicing tabs proceed to a preamplifier 14, followed by an amplification stage 15. The latter drives a power amplifier 16 which in turn drives a loudspeaker 17. A control voltage derived from a voltage divider l8 actuated by an expression pedal 19 (FIG. 3) is applied to lead 20. That control voltage is applied as a gain-control signal to preamplifier 14, so that the loudness of sound radiated by the loudspeaker 17 is a function of the position of band-pass filter which has an adjustable peaking frequency as a function of control voltage, and a relatively low O which varies between values of about 2 and 5 as the control voltage varies. Peak frequencies may vary from about 300 Hz. to about 1.5 kc., as the control voltage varies. The output of filter 30 proceeds via a tab switch 31 to preamplifier stage 15, following the preamplifier 14 which is subject to gain control. Stage 14 may be incorporated in preamplifier 15. The expression pedal thus simultaneously controls gain of the conventional organ output, and tonal characteristics of a subsidiary output which itself has constant gain.

The dynamic filter 30 includes an input terminal 40 and an output terminal 41. See FIG. 3. A first transistor amplifier stage 42 employing a transistor T, in an emitter follower configuration having circuitry arranged to provide a band-pass filter response having a peak at about 1.5 kc. and drives the base of an output transistor T, arranged to operate as a linear amplifier, and the collector of the latter is coupled to output terminal 41.

The emitter follower T, also drives a feedback loop, including in cascade a voltage-controllable diode gate 44, a phasereversing amplifier 45 employing transistor T and an emitter follower stage 46 which provides a low resistance feedback point.

More specifically, the input terminal 40 is connected to the base of T via blocking capacitor C isolating resistance R,, filter capacitor C,. A bias circuit for the base of T, extends from a positive voltage supply 48, to ground via resistances R A and R in series with each other. The junction of the latter resistances is connected to the base of T,. A small collector resistance 49 is provided and an emitter load, consisting of resistances 50 and 51 connected in series to ground, in the order named. A resistance R, is connected between the emitter of T, and the junction of R, and C,. Circuit values are provided in the drawings.

The gain of the amplifier 42 is a function of frequency, as follows:

liaise-swat on the assumption that the junction of R,, R, is at AC ground potential, as is also the junction of R R,,. S is the usual symbol for complex frequency.

The actual ground is provided by the emitter follower resistance R; of T This accounts for the presence of terms R ,R, /R,+R, and R R,,/R,,+R,,.

Assuming zero feedback from T the characteristic of the amplifier is that illustrated at B of FIG. I.

The AC output voltage available at point 60, at the junction of resistances 50, 51, is applied through resistances 61, capacitor 62 to the cathode of diode D,. That cathode is connected to ground through a resistance 63. The relative values of 61 and 63 essentially determine the signal level transmitted to diode D,, the capacitor 62 introducing low frequency rolloff and thus introducing minor filtering into the feedback path which assists in controlling low frequency response. The anode of d is connected to the anode of diode D in a backto-back configuration and the anode of D is connected to ground via resistance 64. The anodes of D, and D, are connected to control lead 20, via R, to which is applied control voltage decreasing as a function of extent of depression of expression pedal 19.

The cathode of D is connected to ground via a resistance 65, and through a coupling capacitor 66 to the base of transistor T Transistor T, has a grounded emitter and a collector load 70. A bias circuit and feedback is connected from side of which communicates with the junction of R, and C and Diodes D and D provide gating of signal through the feed back path. in absence of control voltage at the anodes of D D the gate represents an open circuit and therefore there is no feedback. The filter characteristic is then of type B, FIG. 1 of the accompanying drawings.

With no feedback the filter characteristic is determined by the values of C C and associated resistances, as seen from point G.

As control voltage to the gate is increased, the feedback loop becomes more and more effective. This has the effect of increasing the effective capacitances of C and of C and of the associated resistances. If we consider Here S is complex frequency. With feedback, the overall gain is where -K is gain of the feedback loop.

The net effect is to increase the last term of the denomina' tor of G by a factor of K, K depending on the impedance of the gate as a controllable factor, an since the last term of the denominators Y and T are the same, except for the factor K, the net effect of the feedback loop is to increase the effective values of all frequency-determining values of the filter in the same degree.

The mathematics of the system are approximate, so that the several curves of FIG. I are only approximately identical in shape, but the relative accuracy of the mathematics is attested to by the similarity of shape of the several curves representing different values of gating voltage. Some deviation of the frequency response of the actual circuit from calculated response as a result of phase shift in the amplifier 45 which was assumed to have 180 phase shift in the calculated expressions. The dots on curves A and 8 represent points 3 db. down, and indicate circuit Q. Calculations of Q are not provided.

lclaim:

l. A tunable band-pass electronic music voicing system, including a tone signal input terminal,

a transistor amplifier having an input control electrode, said transistor amplifier having an output circuit,

a first tone filter capacitor connected in series between said signal input terminal and said control electrode,

means including a further amplifier connected in cascade with said output circuit,

said further amplifier having a grounded resistive output circuit,

a second tone filter capacitor connected between a point located between said terminal and said first capacitor and an ungrounded point of said grounded resistive output circuit,

said further amplifier being arranged to introduce only a single phase reversal between said terminal and said grounded output circuit, and

an output circuit means for said first mentioned transistor amplifier.

2. The combination according to claim 1, wherein said means including a further amplifier further includes an AC gate connected in series between said output circuit of said transistor and an input circuit of said further amplifier, said AC gate being responsible to a control voltage to vary its impedance.

3. The combination according to claim 2, wherein said load circuit means includes a further amplifier responsive to signal in said output circuit connected to said first mentioned transistor amplifier, and

a loudspeaker driven from said further amplifier.

4. A tunable tone signal voicing filter having a band-pass characteristic, comprising a first transistor amplifier having a base electrode, a collector electrode and an emitter electrode,

a first load resistance connected between said emitter electrode and ground,

a signal input terminal,

a capacitive tone signal filter connected in series between said signal input terminal and said base electrode,

a second feedback transistor amplifier including at least one further transistor having a base electrode, an emitter electrode and a collector electrode, said second transistor amplifier being arranged to introduce only one phase reversal,

means driving said second transistor amplifier from said first load resistance,

a second load resistance connected between the emitter of said second transistor and ground,

a capacitive tone signal filter feedback connection between an ungrounded point of said second load resistance and a point between said signal input terminal and said capacitive tone signal filter,

a bias circuit for said first transistor including a resistance connected between said base of said first transistor and ground, and

a load device for said first transistor.

5. The combination according to claim 4, wherein said means includes a voltage-controlled gate connected between an ungrounded point of said first load resistance and the input circuit of said second transistor amplifier.

6. The combination according to claim 5, wherein said load device includes another amplifier responsive to tone signal across said first load resistance, and a loudspeaker coupled to be driven by said another amplifier.

7. The combination according to claim 6, wherein said capacitive tone signal filter and said capacitive-tone signal filter feedback connection have substantially equal capacitances.

8. A tone signal band-pass amplifier having adjustable peaking frequencies comprising a first tone signal amplifier stage having a first series capacitive tone filter in series with an input circuit of said amplifier and having a first output circuit,

a negative feedback tone signal amplifier connected in cascade between said output circuit and said input circuit, said negative feedback tone signal amplifier having a further output circuit,

a second series tone signal capacitor connected from said further output circuit and via said first series capacitive tone filter in driving relation to said first tone signal amplifier, and

a variable voltage-responsive impedance between said first output circuit and a drive circuit for said negative feedback tone signal amplifier.

9. The combination according to claim 8, wherein said variable voltage responsive impedance includes a voltage-responsive AC diode gate having back-to-back diodes, and means for applying control voltage to the junction of said gates.

10. The combination according to claim 9, wherein said diode gate includes at least one low frequency rolloff capacitor connected in series with said back-to-back diodes.

11. A dynamic band-pass tone signal filter having constant gain with variable peaking, comprising connected a first transistor filter stage having a transistor in an emitter follower configuration and having a band-pass filter response, and r a feedback loop driven by said transistor, said feedback loop including a controllable diode gate exhibiting voltage-controllable impedance to said tone signal, said feedback loop further including a phase-reversing amplifier providing a low-resistance feedback point coupled to drive said first transistor filter stage.

12. A variably peaking wideband signal band-pass filter comprising a first transistor amplifier having an input circuit and an output circuit, and

a negative feedback path coupling said output circuit to said input circuit, said feedback path including a variable impedance voltage-responsive diode gate capable of transferring said tone signal.

13. The combination according to claim 12, wherein said feedback path further includes a series low frequency rolioff capacitor.

14. The combination according to claim 13, wherein said input circuit further includes a first series connected tonea

Claims

1. A tunable band-pass electronic music voicing system, including a tone signal input terminal, a transistor amplifier having an input control electrode, said transistor amplifier having an output circuit, a first tone filter capacitor connected in series between said signal input terminal and said control electrode, means including a further amplifier connected in cascade with said output circuit, said further amplifier having a grounded resistive output circuit, a second tone filter capacitor connected between a point located between said terminal and said first capacitor and an ungrounded point of said grounded resistive output circuit, said further amplifier being arranged to introduce only a single phase reversal between said terminal and said grounded output circuit, and an output circuit means for said first mentioned transistor amplifier.

3. The combination according to claim 2, wherein said load circuit means includes a further amplifier responsive to signal in said output circuit connected to said first mentioned transistor amplifier, and a loudspeaker driven from said further amplifier.

4. A tunable tone signal voicing filter having a band-pass characteristic, comprising a first transistor amplifier having a base electrode, a collector electrode and an emitter electrode, a first load resistance connected between said emitter electrode and ground, a signal input terminal, a capacitive tone signal filter connected in series between said signal input terminal and said base electrode, a second feedback transistor amplifier including at least one further transistor having a base electrode, an emitter electrode and a collector electrode, said second transistor amplifier being arranged to introduce only one phase reversal, means driving said second transistor amplifier from said first load resistance, a second load resistance connected between the emitter of said second transistor and ground, a capacitive tone signal filter feedback connection between an ungrounded point of said second load resistance and a point between said signal input terminal and said capacitive tone signal filter, a bias circuit for said first transistor including a resistance connected between said base of said first transistor and ground, and a load device for said first transistor.

7. The combination according to claim 6, wherein said capacitive tone signal filter and said capacitive tone signal filter feedback connection have substantially equal capacitances.

8. A tone signal band-pass amplifier having adjustable peaking frequencies comprising a first tone signal amplifier stage having a first series capacitive tone filter in series with an input circuit of said amplifier and having a first output circuit, a negative feedback tone signal amplifier connected in cascade between said output circuit and said input circuit, said negative feedback tone signal amplifier havinG a further output circuit, a second series tone signal capacitor connected from said further output circuit and via said first series capacitive tone filter in driving relation to said first tone signal amplifier, and a variable voltage-responsive impedance connected between said first output circuit and a drive circuit for said negative feedback tone signal amplifier.

11. A dynamic band-pass tone signal filter having constant gain with variable peaking, comprising a first transistor filter stage having a transistor in an emitter follower configuration and having a band-pass filter response, and a feedback loop driven by said transistor, said feedback loop including a controllable diode gate exhibiting voltage-controllable impedance to said tone signal, said feedback loop further including a phase-reversing amplifier providing a low-resistance feedback point coupled to drive said first transistor filter stage.

12. A variably peaking wideband signal band-pass filter comprising a first transistor amplifier having an input circuit and an output circuit, and a negative feedback path coupling said output circuit to said input circuit, said feedback path including a variable impedance voltage-responsive diode gate capable of transferring said tone signal.

13. The combination according to claim 12, wherein said feedback path further includes a series low frequency rolloff capacitor.

14. The combination according to claim 13, wherein said input circuit further includes a first series connected tone-signal filter capacitor for said tone signal and wherein said feedback path includes a transistor amplifier connected in cascade with said diode gate and providing a low-impedance coupling resistance, and a further series tone-signal filter capacitor connected between said coupling circuit and via said series-connected tone-signal filter capacitor to complete said feedback path.