US3585898A

US3585898A - Musical instrument tuning reference standard

Info

Publication number: US3585898A
Application number: US18909A
Authority: US
Inventors: Peter Davidson
Original assignee: Hammond Corp
Current assignee: Marmon Co
Priority date: 1970-03-12
Filing date: 1970-03-12
Publication date: 1971-06-22
Anticipated expiration: 1988-06-22

Abstract

A reference standard for supplying E at 330 Hz. for tuning a guitar or similar instrument. This is accomplished by taking the standard 60 Hz. powerline frequency, dividing it by two to get a 30 Hz. fundamental with odd harmonics and isolating the 11the harmonic by dynamic filtration. The final signal has the desirable range of harmonics accompanying the 330 Hz. fundamental. Variations are shown, including adapting the system for operation on 50 Hz. powerline frequency.

Description

United States Patent 1 1 3,585,898

[72] Inventor Peter-Davidson [56] ReferencesCited IN m UNITED STATES PATENTS gm" n mo 2,901,699 8/1959 Motzetal 324/78 45] rammed 3,383,452 5/1968 Parketal.... 84/].ll m] cc m on 3,412,116 10/1969 Schott 34/454 3,501,992 3/1970 Osbornetal. 84/454 Primary Examiner-Richard B. Wilkinson Assistant Examiner-Lawrence R. Franklin Anomey-Gradolph, Love, Rogers and Van Sciver [54] MUSICAL TUNING EFERENCE ABSTRACT: A reference standard for supplying E at'330 Hz.

STANDARD 7 for tunmg a guitar or s milar lnstrument. This is accomplished 4 8* I by taking the standard 60 Hz. powerline frequency, dividing it [52] US. Cl 84/454, by two to get a 30 Hz. fundamental with odd harmonics and 84/l .01, 84/DlG. 18 307/260 isolating the llthe harmonic by dynamic filtration. The final 5 I] lit. CL. G10 7/02 signal-has the desirable range of harmonic: accompanying the (50] Field olSareh 84/ l .01, 330 Hz. fundamental. Variations are shown, including adapt- L] l, 1.19, 4545307/260; 340/384 E ing the system for'ope'ration on 50 Hz. powerline frequency.

6 19 I l -{8 J8 lgg 20 4, 4 1' 33. 74 44 a; ,64 /76 K I xAI 9; 102

MUSICAL INSTRUMENT TUNING REFERENCE STANDARD BACKGROUND OF THE INVENTION 1. Field of the Invention Tuning reference standards for tunable musical instruments such as guitars, for instance.

2. Description of the Prior Art In the past many different types of tuning reference standards have been employed or suggested. Those most customarily used are other musical instruments of fixed pitch, pianos or organs, for instance, if they are present, or such portable devices as pitch pipes or tuning forks. Electronic oscillators have also been used, but are rather expensive if sufficie ntly precise. Just what note the standard is supplied for is not particularly important, but for a guitar or other fretted instrument it is preferable if the standard is such that one of the strings can be adjusted to zero beat therewith when the string is open, that is, when the string is not pressed against any of the frets.

SUMMARY OF THE INVENTION At present one of the most popular tunable instruments is the electronically amplified guitar. This suggests that it would be an advantage to supply some sort of electronic tuning reference standard in connection with the amplifier, if this could be done at reasonable expense considering the precision required. Investigation of the problem disclosed to the applicant that the E string theoretically should be tuned to 329.6 Hz. when open nonfretted). It also appeared that a reliable ultimate standard frequency generally available is the 60 Hz. powerline frequency. This ordinarily is held at 60 Hz. to within 0.66 Hz. line drift by the power companies and for musical purposes may be considered as nonvariable. The applicant also appreciated that if one took the line frequency of 60 Hz. and divided it by two with an ordinary flip-flop circuit, the result would be a 30 Hz. square wave, which comprises a fundamental accompanied by a declining series of odd harmonies. By proper filtration the eleventh harmonic of this 30 Hz. wave could be selected and by appropriate wave shaping, a declining series of harmonics could. be added thereto, thereby giving a complex wave, with its fundamental at 330 Hz. This is only 0.4 Hz. removed from the theoretical E at 329.6 Hz. The total possible error including the line frequency drift using this approach is, therefore, one-half 0.66 Hz. (possible line drift) +0.4 Hz. or 0.73 Hz. or 0.22 percent. This is well within acceptable limits and for practical purposes can be assumed to be accurate.

' Although circuitry is given hereafter, to accomplish the above, and there may be some specific novelty therein, it is stressed that many different circuit arrangements will occur to those skilled in the art for accomplishing the purpose. The invention, therefore, is believed to reside largely in the realization that the eleventh harmonic of one-half the 60 Hz. line frequency is the E string frequency of a guitar.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I of the drawing is a circuit diagram of mechanism for practicing the invention;

FIG. 2 is a diagram of a variation thereof;

FIG. 3 illustrates an adaptation of the circuit of FIG. 1 to 50 Hz.; and

FIG. 4 illustrates a variation which adapts the circuit of FIG. 1 to both 60 Hz. and 50 Hz.

DESCRIPTION OF THE PREFERRED EMBODIMENT The 60 Hz. line frequency is applied at terminal which is connected to the junction of the cathode end of diode l5 and the base of transistor 12 through resistor 14. The anode end of diode 15 is connected to ground. Therefore, the positive side of the rectified 60 Hz. frequency appears at the base of transistor 12. The emitter of transistor 12 is grounded and the collector thereof is connected through resistor 16 to +12 v. line 18. The value of resistor 14 should be selected such that transistor 12 saturates so as to have a 60 Hz. inverted polarity square wave output at the collector. With the collector output connected to the lower end of the load resistor 16, the output voltage, therefore, becomes negative, or less positive, relative to its previous positive value, when a positive input signal is fed to the base of transistor 12.

The collector is connected by lead 20 to the midpoint of a frequency divider bistable flip-flop comprised of transistors 22 and 24 and associated circuitry. The emitters of transistors 22 and 24 are connected to a l2 v. line 25 and the bases and collectors are cross-connected through identical resistors 26. The midpoint, lead 20, is connected by capacitor 28 and resistor 30 in series to the collector of transistor 22 and by capacitor 32 and resistor 34 in series to collector of transistor 24. The junction between capacitor 28 and resistor 30 is also connected to transistor 22 base through steering diode 36 and the base is connected to lead 25 through resistor 38. Identical connections through steering diode 40 and resistor 42 are supplied at the opposite side of the circuit. The diodes are oriented as shown with the positive terminals connected to the bases. With the output signal that appears at the collector of transistor 12 being applied simultaneously to transistors 22 and 24, the use of negative pulse steering diodes eliminates switching time delays. The collector of transistor 22 is connected to the positive lead 18 through resistor 44 and the collector of transistor 24 is connected through

resistors

46 and 48 in series to lead 18.

This flip-flop operates in conventional manner so that the input frequency is divided by two and a 30 Hz. square wave appears at the junction between

resistors

46 and 48. The remainder of the circuit selects the eleventh harmonic and perfonns a wave shaping function.

The junction between

resistors

46 and 48 is connected through

capacitors

50 and 52 in series to the base of transistor 54. The base is also connected to ground through resistor 56 and variable resistor 58 in series. The emitter is connected to lead 25 through resistor 60 and the collector to line 18 through load resistor 62.

The collector of transistor 54 is connected to the base of a second transistor 64 the emitter of which is connected to B+ lead 18 and the collector to l2 v. line 25 through resistor 66. There is also a feedback connection from the collector of transistor 64 through resistor 68 back to the common point between

capacitors

50 and 52 and a connection from the collector of transistor 64 through resistor 70 to the emitter of collector of transistor 64.

With appropriate values in this circuit to be given presently,

the input to transistor 54 acts as a high pass filter and the two transistors act as an amplifier which because of the feedback paths tends almost to oscillate at the eleventh harmonic, 330 Hz., when the variable resistor 58 is properly adjusted for maximum output voltage at the mentioned frequency. The output from this portion of the circuit appears at lead 72 connected to the collector of transistor 64. The active filtered signal which appears at lead 72 is at the frequency of 330 'Hz., however, modulated at 30 Hz. The pulsed wave train modulation pattern is free of quiescent regions and appears as a repetitious series of damped waves, wherein, the peaks decline in amplitude, with 11 cycles per second present per modulation cycle.

The damped wave train at the proper frequency in lead 72 is connected through

resistors

74, 76 and 78 in series in that order to the base of a transistor 80. Resistor 76 is variable. The junction between

resistors

74 and 76 is connected to ground through resistor 82, and the base of transistor 80 has a high frequency path to ground through capacitor 84. The input resistor-capacitor mesh to transistor 80, therefore, acts as a low pass filter and discriminates against frequencies above the fundamental at 330 Hz.

The emitter of transistor 80 is connected to lead 25 through resistor 86 and the collector is connected to the lead 18 by resistor 88. The collector of transistor 80 is connected to the base of a second stage transistor 90, the emitter of which is connected to line 18. The collector of transistor 90 is connected to output lead 92 and to line 25 through resistor 94. Feedback paths are provided from the collector of transistor 90 to the emitter of transistor 80 through resistor 97 and from the collector of transistor 90 through capacitor 96 to the midpoint between

resistors

76 and 78.

The circuit of transistors 80 and 90 is essentially similar to that of

transistors

54 and 64 excepting that the circuit of transistors 80' and 90 emphasizes the 330 Hz. frequency and discriminates against spurious signals at a frequency above 330 Hz. by attenuating at 12 db. per octave whereas the cir cuit with transistors 54--64 emphasizes the 330 Hz. frequency and introduces some spurious higher frequencies in doing so. Resistor 76 is adjusted for maximum reliable signal output operation with a minimum of resistance, which provides the desired locked-to-the-line coupling and the smoothest output wave at terminal 92. The adjustable resistors 58 and 76 will adjust about the midpoint, for proper setting, with the related optimized RC components.

The circuit as so far described would give a good approximation of a sine wave at line 92. Preferably, this is changed so as to produce some harmonic development, since the tone produced by such a signal is easier to tune to. This is accomplished by the resistor 100 and diode 98 connected to ground. The diode shunts the signal at output 92 and produces a nonsymmetrical wave. The value of the resistor can be selected as desired to produce a pleasing tone. Connected to the junction formed by resistor 100 and diode 98 are two series resistors, 101 and 102, which are also connected to ground. The resistors form a voltage divider with tenninal 93 taken between the resistors at the required output voltage. The output terminal 93 with the 330 Hz. signal thereon may be connected to its own amplifier and speaker of conventional design, or as usually will be the preferred arrangement, it can be connected into the normally present guitar amplifier circuit so as to make use of the guitar amplifier and speaker.

The values of the components in the representative circuit shown and discussed are as follows:

' Transistors 64 and 90, type 2l l7 Other transistors, type 2108 Diodes l and 98, type 2603, and 36 and 40, type 2601 Resistors in ohms:

8 470 82 K L 1 66, 94 K 3. 9 16, 44, 46 K 5. 6

4, 78 K 22 100 K 33 60, 86 K 39 102 -K 47 76 K 50 38, 42 K 56 30, 34, 58, 62, 88, 101 -K 100 26, 56 K 150 Capacitors in microfarads:

28, 32 (disc) 001 84 (mylar) 001 50, 52 075 96 47 The circuit described in detail above divides the input 60 Although we prefer this arrangement, it is also, of course, possible to take the eleventh harmonic of the input frequency and subsequently divide the resulting 660 Hz. frequency by two and wave shape the resulting 330 Hz. E signal so as to obtain a similar end result. To accomplish this, FIG. 2, the input essentially sine wave signal is saturated at 110, as in the transistor 12 circuit in the previous embodiment. The saturated signal is fed into adynamic high pass filter 112 similar to the one shown at 54, but adjusted to give a 660 Hz. signal modulated at 60 Hz. rather than 330 Hz. signalmodulated at 30 Hz. This 660 Hz. signal is applied to a pulsed clipper or trigger circuit 114 which may be of conventional type. The output from this circuit which has a steep wave front is fed to a bistable flip-flop 116, such as at 22-24 which divides the frequency by two to give 330 Hz. which can be wave shaped as at 118 to give a signal at 120 substantially identical to that at 93.

Although it is not the primary objective, the circuit of FIG. 1 can easily be converted to serve as a tuning reference when the available power line frequency is 50 Hz. rather than 60 Hz., thereby making the systems as supplied for 60 Hz. useful in many countries where 50 Hz. is standard. This is accomplished by converting the circuit to supply the seventh harmonic of 50 Hz. which is 350 Hz., very close to true musical F at 349.228 Hz. To make the conversion it is necessary merely to install a connection between lead 20 and the junction between resistor 46 and transistor 24 and to remove or disconnect load resistor 16. Note that when lead 20 is connected to resistor 46,

resistors

48 and 46 serve as the load in place of resistor 16. The connection from lead 20 through resistor 46 to the input of transistor 54 bridges the frequency divider 22-24 and the saturated 50 Hz. signal is, therefore, applied directly to transistor 54. The only other changes necessary are to adjust the settings of resistors 58 and 76 to accommodate the higher frequency.

In making this adjustment, resistor 58 will be moved from approximately its midpoint to about one-third of its resistance value. This reduces the total resistance 58+56 by ll.l percent. Resistor 76 is also adjusted to reduce its value similarly. These two adjustments take care of the frequency increase of 6.06 percent (from 330 Hz. to 350 Hz.). The portion of the circuit affected by this change is shown in FIG. 3 where the bridge across the frequency divider is indicated at 120 and resistor 16 of FIG. 1 has been eliminated.

Of course, the elements of the frequency divider could be eliminated from the circuit if the circuit is to operate from a 50 Hz. supply, but usually it is less expensive to make the systems all alike and convert the few that are to be used where 50 Hz. is standard. If desirable, to accommodate both standards, a single pole double throw switch 122, FIG. 4, can be connected so that when in one position it connects lead 20 to resistor 16 for 60 Hz. and in the other position connects lead 20 to lead 120 for 50 Hz. Switches, not shown, can also be installed to switch in and out preset resistors of appropriate values at 58 and 76.

From the above it will be apparent that the system illustrated and described provides an E signal at 330 Hz. for tuning purposes that is as precisely regulated as is the 60 Hz. power circuit with which it is used. For all practical purposes they may be considered as absolute regulation and is in fact more precise than most tuning standards customarily used. Also the system has the advantage of being easily convertible for operation on 50 Hz. standard frequency.

Having described the invention what I claim is:

1. A circuit for providing a musical instrument tuning reference signal comprising circuit means for receiving the standard alternating current power line frequency at 60 Hz., means for dividing said powerline frequency by two to provide a signal at 30 Hz. said dividing means acting on said signal to provide said 30 Hz. signal with a series of odd harmonics, and means for extracting the eleventh hannonic from said dividing means signal to provide a tuning reference musical E signal at 330 Hz.

2. The circuit of claim 1 in which the means for extracting the eleventh harmonic is a feedback amplifier conditioned so as almost to oscillate at 330 Hz.

3. The circuit of claim 1 in which said dividing means is a bistable flip-flop.

4. The circuit of claim 3 in which the means for extracting the eleventh harmonic is a feedback amplifier conditioned so as almost to oscillate at 330 Hz.

5. The circuit of claim 1 including means for distorting said 330 Hz. signal to add a series of even and odd harmonics thereto.

6. The circuit of claim 5 in which the means for extracting the eleventh harmonic is a feedback amplifier conditioned so as almost to oscillate at 330 Hz.

7. The circuit of claim 5 in which the distorting means is a diode.

8. The circuit of claim 7 in which the means for extracting the eleventh harmonic is a feedback amplifier conditioned so as almost to oscillate at 330 Hz.

9.. The circuit of claim 5 in which said dividing means is a bistable flip-flop.

10. The circuit of claim 9 in which the means for extracting the eleventh harmonic is a feedback amplifier conditioned so as almost to oscillate at 330 Hz.

11. The circuit of claim 9 in which the distorting means is a diode.

12. The circuit of claim 11 in which the means for extracting the eleventh harmonic is a feedback amplifier conditioned so as almost to oscillate at 330 Hz.

13. A circuit for providing a musical instrument tuning reference signal comprising an input for receiving a standard alternating current powerline frequency, and means responsive to said frequency for adding a harmonic series to said input frequency and harmonic selecting means to provide an output signal at a selected harmonic of the input signal which selected harmonic is at substantially the fundamental frequency of a note of the musical scale.

14. The circuit of claim 13 in which the means for adding a harmonic series is a saturated amplifier.

15. The circuit of claim 13 in which the harmonic selecting means is a feedback amplifier having tuning means to condition said amplifier almost to oscillate at a selected frequency in the range between 330 Hz. and 350 Hz.

16. The circuit of claim 13 in'which the harmonic selecting means is a feedback amplifier conditioned so as almost to oscillate at 660 Hz.

17. The circuit of claim 16 including means for dividing the frequency of the signal from said feedback amplifier by two.

18. The circuit of claim 13 in which the input frequency is 50 Hz. and the harmonic selecting means selects the seventh harmonic.

19. The circuit of claim 18 in which the means for adding a harmonic series is a saturated amplifier.

20. The circuit of claim 18 in which the harmonic selecting means is a feedback amplifier conditioned so as almost to oscillate at 350 Hz.

Claims

1. A circuit for providing a musical instrument tuning reference signal comprising circuit means for receiving the standard alternating current power line frequency at 60 Hz., means for dividing said powerline frequency by two to provide a signal at 30 Hz. said dividing means acting on said signal to provide said 30 Hz. signal with a series of odd harmonics, and means for extracting the eleventh harmonic from said dividing means signal to provide a tuning reference musical E signal at 330 Hz.

3. The circuit of claim 1 in which said dividing means is a bistable flip-flop.

7. The circuit of claim 5 in which the distorting means is a diode.

9. The circuit of claim 5 in which said dividing means is a bistable flip-flop.

11. The circuit of claim 9 in which the distorting means is a diode.

16. The circuit of claim 13 in which the harmonic selecting means is a feedback amplifier conditioned so as almost to oscillate at 660 Hz.