Musical teaching and tuning apparatus
United States Patent Barnum 1 1 Apr. 22, 1975 1 1 MUSICAL TEACHING AND TUNING APPARATUS {76] Inventor: Phillip R. Barnum, 8031 East Willetta, Mesa, Ariz. 85207 [22] Filed: Sept. 18. 1973 [21] Appl. No.: 398,443  
 Related US. Application Data [63] Continuation-impart of Scr. No. 255.674. May 22.  
 1972. abandoned.  
 [52] US. Cl. 84/454; 84/470; 84/DIG. 18; 324/79 D [51] Int. Cl. GlOg 7/02; G09b 15/00 [58] Field of Search &#34;84/101. 1.03. 1.09-1.11. 84/119. 1.27, 454. 470, 477. DIG. 18; 324/79 R, 79 D [56] References Cited UNITED STATES PATENTS 2.901.699 8/1959 Motz ct a1 84/454 X 3.470.785 10/1969 Shallenberger et a1. 84/470 3.472.116 10/1969 Schott 84/454 3.509.454 4/1970 Gosscl.... 324/79 R 3.541.915 11/1970 Rhodes 84/470 3.631.756 1/1972 MacKworth-Young 84/454 3.722.352 3/1973 lhrke et a1. 84/454 3,722.353 3/1973 Wcsthaver 84/454 1766.818 10/1973 Prohofsky 84/454 3.774.494 11/1973 Reid. Sr. et a1.. 84/470 3.782.237 1/1974 Okamoto 84/470 3.795.169 3/1974 Bclcher..... 84/454 3.817.144 6/1974 Okamoto 84/470 [57] ABSTRACT A crystal-controlled oscillator is utilized in conjunction with a digital frequency divider chain. which divider chain is provided with means for selecting any one of a plurality of division ratios, to derive a selected tone within the tempered scale. The output signal from the divider chain. which is a square wave, is passed through a selected voicing network to provide the approximate timbre of a musical instrument. The amplified signal from the voicing network drives a transducer such as a set of head phones or a loudspeaker. A decibel meter is provided to monitor the intensity of sound issuing from the transducer such that hearing tests across the important part of the frequency spectrum can be readily carried out. Additionally. in order to assist in ear training a pupil and also to achieve means for determining very closely the pitch of an instrument being tuned or otherwise compared against the crystal-controlled standard, a counter chain is used with logic circuits in such a manner that the difference in period between a crystalcontrolled tone and a tone of unknown, but moderately close to very close frequency is measured over every other half cycle for subsequent display on a zero center meter which deflects in one direction to indicate a sharp unknown tone and in the other direction to indicate a flat unknown tone. there being no deflection if the periods of the known and unknown tones are sufficiently close. For interval training a student may be presented with a first precise tone. derived through the divider chain. against which he attempts to adjust a variable frequency oscillator to arrive at an interval indicated on a switch controlling the counter chain. However. that switch adjusts the counter chain in such a manner that it measures a period corresponding to the tone the student is seeking rather than that derived through the frequency divider chain. Thus. the meter display provides an accurate indication as to whether he is sharp or flat with respect to the tone he is seeking.  
 4 Claims, 5 Drawing Figures ammo&#34; coumnoa MLIFIEI 21 f 2: 1 mm cram&#34; EXTERNAL MP0! &#34;I? F LYEI PATENTEDAPRZZHTS SHKU 3 BF 5 lllllllllll WM Q JT QQUW MUSICAL TEACHING AND TUNING APPARATUS This application is a eontinuation-in-part of my copending application Serial No. 255.674. filed May 22. I972. entitled &#34;Musical Teaching and Tuning Apparatus&#34;, and now abandoned.  
  This invention relates to the musical arts. and more particularly. to electronic apparatus for providing ear training as well as means for achieving very accurate tuning and hearing sensitivity tests.  
  Many devices are known in the prior art which purport to issue a more or less accurately tuned pitch against which a musician. craftsman, or student can compare his efforts by ear. Other devices provide a visual indication of differences between a master tone represented in some analog and a tone generated in one manner or another by the operator. For example, the well known pitch pipe. when activated like a harmonica. produces a tone which may be a standard frequency. by way of example, for a particular string on a guitar or violin. The drawback to this type of tuning is that the accuracy achieved is completely determined by the tuners ear with a complicating factor in that the timbre of the sound is different from the timbre of the instrument being tuned. Another device used for tuning guitars comprises six resonant reeds tuned to the six frequencies to which the six guitar strings should be tuned. To use this device. a string is plucked and tuned until the corresponding resonant reed is observed to vibrate with maximum excursion. However. excursion travel is also dependent on the magnitude of the blow that activates the string. and it is very difficult to determine when maximum excursion is achieved.  
  Among the more advanced tuning devices is the socalled strobe tuner which utilizes a motor-driven set of discs rotating at a closely controlled speed. Vibrations from the instrument being tuned are picked up by a microphone and amplified to cause light amplitude fluctuations at a corresponding rate behind the discs which are circumferentially divided into alternating opaque and translucent areas. When the unknown tone is in tune, a selected area along the radius ofthe disc will appear to stand still in accordance with the well-known stroboscopic effect. This apparatus, while useful. has certain distinct drawbacks and limitations. For tuning string instruments, the intensity of the string movement [which is, of course, damped) determines the intensity of the lights such that one must be very adept at making a quick observation. Another problem in utilizing this apparatus in tuning plucked string instruments is that the pitch of the plucked string does not immediately settle down when the string is first plucked or struck. and the transient deviations are variable according to the specific place and method the string is activated. From a teaching standpoint, there is no audio involvement to enhance ear accuracy; i.e.. the apparatus is not intended as a teaching aid but rather as a working tool. It is possible, of course. to use laboratory grade electronic equipment such as a frequency counter to measure the frequency of an unknown sound to a high degree of accuracy. However. those skilled in the electronics art will appreciate that the necessity for additional interface equipment coupled with the expense and complexity of such frequency counters renders such an approach completely impractical for ordinary tuning purposes.  
  As previously noted, the above-described prior art devices. which are only representative, are primarily concerned with providing a tool with which an experienced musician or craftsman can tune an instrument. None of the known prior art devices provide means by which an unskilled person can compare his tuning efforts against a master tone to a very fine degree of accuracy. whether for the purpose of tuning or ear training.  
  Thus. it is a broad object of my invention to provide improved apparatus for facilitating tuning and musical ear training.  
  It is another object of my invention to provide such apparatus which provides an unmistakable visual indication of the qualitative difference between a preselected, accurate tone, and a tone of unknown fre quency produced by the efforts of the operator.  
  It is still another object of my invention to provide such apparatus which indicates the interval difference between an accurately generated tone and a tone generated under control of an operator which should be at a predetermined interval.  
  It is still a further object of my invention to provide apparatus which permits the foregoing comparisions at all intervals including the octave. across a range ofseveral octaves.  
  It is yet another object of my invention to permit such comparisons to be made in the timbre of the different instruments to create familiarity with the characteristic sounds of such instruments.  
  In yet another aspect. it is an object of my invention. by virtue of the accurate pitch and sound level control inherent therein. to provide apparatus for readily carry ing out standardized hearing tests across the most important portion of the audio spectrum.  
  Yet another object of my invention is to provide such apparatus which is reliable, simple to use, and relatively inexpensive to produce.  
  The subject matter of the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention. however. both as to organization and method of operation, may best be understood by reference to the following description taken in connection with the accompanying drawings, of which:  
  FIG. 1 is a block diagram ofa presently preferred embodiment of the invention.  
  FIG. 2 is a schematic representation of the electrical components and circuitry utilized in the emobodiment of the crystal oscillator 1, frequency divider chain 2. and tone selector switch 3.  
  FIG. 3 is a schematic representation of the electrical components and circuitry utilized in the embodiment of the period gate logic l2, counter and decoder 13 and period selector switch 14.  
  FIG. 4 is a schematic representation of the electrical components and circuitry utilized in the embodiment of the isolation amplifer 24 and period (count) comparator 18.  
  FIG. 5 is a schematic representation of the electrical components and circuitry utilized in the embodiment of the squaring circuit and filter network 23.  
  Referring now to FlG. I, it will be observed that a crystal oscillator 1, having a nominal frequency of 3.87l87l mhz for reasons which will be set forth below. drives a frequency divider chain 2 which has a division ratio under control of a tone selection switch 3.  
 Frequency divider chain 2 is preferably of the digital. integrated circuit type which has become widely available in recent years. Those skilled in the art will appreciate that different division ratios are readily achieved by variously interconnecting the adjacent stages and feedback between nonadjacent stages of the divider chain according to well known techniques. The presently preferred electrical embodiment of crystal oscillator 1. frequency divider chain 2 and tone selector switch 3 is depicted in FIG. 2. Frequency selection is the function of the tone selector switch 3 which is pref erably calibrated in indicia indicating both the frequency output of the divider chain 2 and the corresponding note on the tempered scale. Thus. if the switch is preset to the position 440-A&#34; the interconnections between the stages and the frequency divider 2 will afford a division ratio of 8800 whereby the actual output frequency from the divider will be 439.99. The other tones of the tempered scales may be derived with similar accuracy by varying the division ratio of the frequency divider chain 2, and has been found that the previously indicated crystal frequency of 3.871871 mhz is optimum for achieving close accuracy in the derivation of all the tones desired without the undue cost and propagation time difficulties associated with higher frequencies.  
  After the signal from the master oscillator has been divided by the frequency divider chain 2 to the selected audio tone. the audio tone passes through a mode selector switch 4 and is impressed on the input terminals of a plurality of SPST switches 5a, Sb. 5c. 5d. .5 to select one or more of the voicing circuits 6a. 6b. 6c. 6d. .6&#34; in order to alter the waveform to provide the timbre of a given instrument.  
  The conditioned tone is then amplified by an amplitier 7 by an amount determined by the position of volume control 8 to drive a sound transducer such as the head phones 9 or speaker 10. Additionally. a decibel meter It is utilized to monitor the intensity of the tone impressed on the sound transducer in order that the apparatus may be used to test the hearing acuity ofa person across the audio spectrum controlled by the tone selector switch 3. In a presently preferred embodiment of the invention. the apparatus covers three chromatic octaves extending one and one-half octaves on each side of middle C.  
  It is apparent that the apparatus. as so far described, may be utilized to generate a very closely controlled tone of a selected frequency which a trained musician or craftsman can readily use to tune an instrument. However, a prime merit of the apparatus is its versatility including the ability to visually compare known and unknown tones for tuning and training purposes as will become apparent while the description proceeds.  
  In order to compare the frequency of an unknown audio signal against that of a known standard frequency, it is desirable to integrate the standard signal for a predetermined number of cycles to arrive at a period which can be compared against the period of the unknown signal. This approach permits an expansion of the known and unknown period difference in accordance with the precise number of oscillator cycles comprising a standard period. Referring again to FIG. 1, it will be observed that the output signal from the crystal oscillator 1 is also applied to period gate logic 12. The output from the period gate logic 1! drives a counter and decoder 13 which counts a number of cycles from the crystal oscillator l determined by the setting of a period selector switch 14. The period selector switch 14, similar to the tone selector switch 3, functions to variously interconnect adjacent stages and feedback among the several stages in the counter chain in the counter and decoder 13 such that an output signal will issue when the counter reaches a predetermined count. As those skilled in the digital arts will appreciate. this can be carried out either with preset counter techniques or straightforward decoding. The presently preferred electrical embodiment of the period gate logic l2. counter and decoder 13, and period selector switch 14 is depicted in FIG. 3. By way of example. if the counter and decoder 13 issues an end of period signal after receiving 440 counts from the crystal oscillator 1., the period between the beginning of the first count and the end of the last count will be the one-half the period of a standard 440-A. i.e.. approximately l/880th of a second.  
  A tunable audio oscillator 15, under operator control by means of tuning knob 16, is coupled through input selector switch 17 to one of the terminals of the mode selector switch 4. Therefore. if the mode selector switch is thrown to its alternative position. the tone generated by the audio oscillator 15 is passed through the selected voicing circuit for audible reproduction through the head phones 9 or speaker 10. Additionally. the output from the audio oscillator 15 is coupled to the period gate logic l2 and through isolation amplifier 24 to the gating period comparator 18. Preferably the output waveform from the audio oscillator 15 approximates a square wave to properly drive the voicing circuits and also to accurately institute and stop logical action in the period comparator network. The presently preferred electrical embodiment of the isolation amplifer 24 and period comparator 18 is depicted in H0. 4.  
  Assume that an operator is attempting to tune the audio oscillator 15 to an A at 440 Hz. This tuning effort is carried out by setting the tone selector switch 3 to the appropriate position and throwing the mode selector switch 4 back and forth between its alternate positions for audible comparison of the standard tone and the operator produced tone. When the operator wishes to make a determination of the accuracy with which he has tuned the audio oscillator 15, he may institute a comparison cycle. and the leading edge of a cycle from the audio oscillator 15 is utilized to open gates in the period gate logic 12 which permit the signal from the crystal oscillator l to pass into the counter and decoder 13 which commences to count toward 440 as selected by the period selector switch 14. When the count of 440 is reached, the feedback loop 19 carries the end of period&#34; signal back to the period gate logic 12 to inhibit further counting. Simultaneously. the end of period signal is impressed on the period comparator 18 which. at approximately the same time. senses the trailing edge of the same half cycle from the audio oscillator 15. According to the accuracy to which the audio oscillator 15 has been tuned. the end of period&#34; signal from the counter and decoder 13 and the trailing edge of the same half cycle from the audio oscillator 15 may arrive simultaneously or the signal from the audio oscillator may slightly lead or lag the end of period&#34; signal. if the leading edge of the signal from the audio oscillator l5 arrives slightly early. its period is shorter than U440 of a second. and the audio oscillator is therefore tuned sharp. Similarly, if the signal from the oscillator lags the end of period&#34; signal slightly, its period is longer than l/44O of a second, and the audio oscillator is therefore tuned slightly flat.  
  Thus, the output signal from the period comparator l8 impressed across the input terminals to a different amplifier will be zero if the periods are the same and either mutually positive or negative if the unknown frequency is sharp or flat. Differential amplifier 20 is provided with zero adjust control 21 to initially set the reading on the pitch meter 22 to center scale. Thereafter, lack of coincidence between the termination of the known period and the unknown period will cause either a sharp or flat reading on the pitch meter 22 with the amount of deflection corresponding to the degree to which the periods differ. It has been found in training new students that full scale deflection should be on the order of 5 percent off pitch although those skilled in the art will understand that it is a simple matter to vary the gain of the differential amplifier 20 or otherwise alter the sensitivity of the deviation observed on the pitch meter 22.  
  For tuning instruments with the assistance of the pitch member 22, the input selector switch 17 may be thrown to its alternate position which accepts signals from a squaring circuit and filter network 23 that is driven from an external input which may be, by way of example, a microphone or other pickup in communication with a musical instrument being tuned. The squaring circuit and filter network 23 must be of specialized design to function properly with harmonic-rich inputs such as that of musical instruments and the schematic representation of one satisfactory electrical embodiment is shown in FIG. 5. The output signal from the squaring circuit and filter network 23 cooperates with the frequency comparator section of the apparatus in precisely the same manner as that already described for the audio oscillator 15. Additionally, it will be apparent that ear tuning of the external input may be carried out by operating the mode selector switch 4 between its alternate positions.  
  ln carrying out somewhat more advanced ear training, one must become adept at recognizing intervals. For example, a common interval is a minor 3rd constituting 3 half tones such as from A to C. in order to utilize the apparatus to test facility in selecting and recognizing intervals, the operator of the audio oscillator 15 may be asked to tune the oscillator to a C while listen ing to an A through the head phones 9 or the speaker 10. Thus, the tone selector switch 3 is set to pass an A through the voicing circuits whereas the period selector switch 14 is set to extract the period of a C. The operator selectively throws mode selector switch 4 to its alternative positions while tuning the audio oscillator 15 until he believes he is hearing the corresponding interval between the two tones. A period comparison may then be carried out to determine whether he has the correct interval and also how accurate his frequency selection has been as indicated by the reading observed on the pitch meter 22. it will be apparent that any desired interval, including octaves and intervals in excess of octaves may be selected by appropriate adjustment of the tone selector switch 3 and the period selector switch 14. Similar interval experimentation may be earried out utilizing the external input in conjunction with an operator controlled musical instrument.  
  it will also be apparent to those skilled in the art that the mode selector switch 4, depicted as manually operable in FIG. 1, may be automatically or electronically actuated to facilitate comparison by the operator and alleviate the operation of mechanically switching by the operator.  
  While the principles of the invention have now been made clear in an illustrative embodiment, there will be immediately obvious to those skilled in the art many modifications of structure, arrangement. proportions, the elements, materials, and components. used in the practice of the invention which are particularly adapted for specific environments and operating requirements without departing from those principles.  
 I claim:  
 1. Musical teaching and tuning apparatus comprising:  
 a. a crystal controlled oscillator;  
 b. a digital frequency divider coupled to the output ofsaid oscillator for dividing the frequency thereof;  
 c. means for selecting the ratio by which said frequency divider divides the output signal from said crystal oscillator;  
 d. a plurality of voicing circuits;  
 e. means for coupling at least one of said voicing circuits to the output of said frequency divider. output terminals of coupled ones of said voicing circuits being common;  
 f. an amplifier connected to the output from said voicing circuits;  
 g. means for controlling the gain of said amplifier;  
 h. an acoustic transducer driven by said amplifer for reproducing an audio tone derived from said crystal oscillator by said frequency divider and shaped by at least one of said voicing circuits; a tunable audio oscillator; and  
  mode selector switch means for selecting between the output from said frequency divider and the output from said tunable audio oscillator as the input to said voicing circuits.  
 2. The musical teaching and tuning apparatus of claim I, which further includes:  
 a. a squaring circuit for accepting an audio frequency input from an external source; and  
 b. an input selector switch for alternatively coupling the output from said squaring circuit and said tunable audio oscillator to said mode selector switch.  
  3. The musical teaching and tuning apparatus of claim 2, which further includes:  
 a. a counter decoder circuit for issuing an output signal in response to a predetermined number of input pulses;  
 b. means for selecting the number of predetermined pulses which cause said counter and decoder to issue an output pulse;  
 c. gating means coupling the output signal from said crystal oscillator to said counter and decoder, said gating means having additional inputs coupled respectively to receive the output signal from said counter and decoder and to receive the output signal from the audio source selected by said input selector switch, said gating means being configured such that the leading edge of an audio cycle from said audio signal source permits said counter and decoder to commense accumulating pulses from said crystal oscillator and said output signal from said counter and decoder inhibits further accumulation of said pulses from said crystal oscillator;  
 d. a period comparator for receiving said output pulses from said counter and decoder and for receiving the next succeeding trailing edge of a cycle from said audio signal source and for issuing a differential signal having a magnitude representing the time difference thcrebetween and a polarity in- 4. The musical teaching and tuning apparatus of claim 1, which further includes a decibel meter disposed in parallel with said acoustical transducer.  
  dicative of the time sequence in which said period comparator receives said signals; and e. a zero center meter driven by said differential signal to thereby indicate that the frequency of the