EP0269652A1 - Tuning aid for musical instruments - Google Patents

Abstract

A device helping to tune a stringed instrument, such as a guitar, includes a phonosensor (14) (preferably independent of the phonosensors contained in the guitar), an electronic circuit that compares the frequency of the signals produced by the phonosensor (14) to a range of recorded digital signals representing frequencies, and a display (15) which indicates when a string is tuned. A simple embodiment is embodied by a lamp (15) which lights up under the string when the latter is tuned. A more complex version has several different modes of operation and the phonosensor includes a separate winding for each string, a selector being included in the electronic circuit which operates so as to select the winding associated with a vibrating string.

Description

TUNING AID FOR MUSICAL INSTRUMENTS

This invention relates to a tuning aid for a musical instrument, particularly, but not exclusively, a stringed instrument.

Tuning aids of various types are already available. One known type produces tones to which the strings of the instrument are to be tuned. Such tuning aids are very difficult to use in a noisy environment. Tuning aids are also available which can be connected to a pick-up on the instrument, while the instrument is disconnected from its amplifier, but these devices are also difficult to use in actual performance situations.

It is one object of the invention to provide a convenient form of tuning aid for a stringed instrument.

In accordance with one aspect of the invention, there is provided a stringed instrument having a tuning aid, said tuning aid comprising a pick-up sensitive to vibrations of the instrument's strings and producing an oscillatory electrical signal of frequency dependent on such vibrations, logic circuit means connected to said pick-up to receive signals therefrom and display means connected to logic circuit means and arranged to indicate when a string is vibrating at a frequency appropriate to that string.

Preferably, the pick-up is separate from an output pick-up on the instrument which is used for providing an output signal to an amplifier. Preferably, also the tuning aid incorporates a battery.

The display device may include a row of lights (such as l.e.d.s), which are situated adjacent respective ones of the strings of the instrument. When the tuning aid is in use, the light adjacent a specific string is lit when that string is vibrating.

The display means may also include further lights to indicate respectively (a) when the frequency of the string is too low, (b) when the frequency is substantially correct and (c) when the frequency is too high.

The display means may have a plurality of lights for each of the functions (a) and (c) mentioned above, the number of lights illuminated being dependent on the magnitude of the deviation of the frequency from the desired frequency (in the manner of a bar type display).

The logic circuit means may comprise counting means arranged to produce a count dependent on the frequency, and digital comparator means for comparing said count with stored data representing the counts which are produced when each string is in tune.

Although, as described above, it is a preferred feature of the invention that the tuning aid be built into the instrument, it is also within the scope of the invention to provide a separate tuning aid embodying the logic circuit means and the display means, which derives its input signal from a pick-up built into the instrument and normally used for driving an amplifier.

It is also within the scope of the invention to provide a separate tuning aid incorporating the logic circuit means and the display means, with its own internal pick-up and power supply for attachment to an instrument.

The invention also includes within its scope a tuning aid incorporating the logic circuit means and the display means and which is adapted to be connected to an electrical output connector on an instrument so that it responds to the a.f. output of the instrument. In this case the tuning aid may include a lead for connection to an amplifier, to pass on the a.f. output of the instrument to the amplifier, or a connector by means of which it can be connected to the amplifier. This form of tuning aid is particularly applicable to electronic keyboard instruments.

The invention also includes within its scope a tuning aid which includes a built-in microphone for use in tuning acoustic instruments (as distinct from electronic instruments) such as acoustic guitars, acoustic bass instruments and wind instruments.

In accordance with another aspect of the invention there is provided a tuning aid for use with a musical instrument and including an input circuit for receiving an oscillatory electrical signal from the instrument to be tuned, conversion means for deriving a first multibit digital signal dependent on the frequency of said signal, reference frequency means for successively producing a plurality of reference multibit digital signals representing reference frequencies, digital comparator means for comparing said first multibit digital signal with said reference multibit digital signals in turn, and display means controlled by said comparator means for indicating the relationship between said frequency and said reference frequencies.

An example of the invention will now be described with reference to the accompanying drawings in which:-

Figure 1 is a fragmentary view of a guitar with a tuning aid installed; Figure 2 is a fragmentary side view of the tuning aid;

Figure 3 is a block diagram of the tuning aid;

Figure 4 is a table showing the contents of an EPROM included in the circuit diagram and

Figure 5 is a block diagram of another example of the invention.

Referring firstly to Figures 1 and 2 , the tuning aid 10 is fitted in the front panel of the guitar body 11 adjacent the conventional pick-up 12 which is used for providing an electrical output to an amplifier. The tuning aid 10 incorporates another pick-up, the pole pieces 14 of which are shown. It also includes a row of lights in the form of l.e.d.s 15 lying in a line parallel to the row of pick-up pole pieces 14 and each underlying a respective one of the strings. The tuning aid has a switch 16 at one end which can be used for turning the tuning aid on and off and, at the other end, it has four further l.e.d.s in a row. The two centre l.e.d.s 17A, 17B are green l.e.d.s which both light when a string is in tune and the outer l.e.d.s 18, 19 are arrow shaped red l.e.d.s to indicate when the string is close to the correct tuning, but sharp or flat. If only one of the l.e.d.s 17A, 17B lights this shows that the string is very close to the correct tuning. The tuning aid includes its own batteries.

The logic circuit of the tuning aid is designed to illuminate the various l.e.d.s when a string is vibrating, in accordance with the tuning state of that string. If the frequency of the signal is at (or very slightly higher than) a specific one of a number of frequencies, one of the l.e.d.s 15 lights and the green l.e.d. 17 lights also. If the l.e.d. 15 which lights is the one under the string which is vibrating, then that string is in tune. The l.e.d.s 18 and 19 are lit to indicate the sense of the error from correct tuning.

The basic principle of the logic circuit is the conversion of the input frequency into a time duration, the counting of a fixed frequency signal into a first counter for that time duration and the comparison of the count thus achieved with count values stored in an EPROM by incrementing an address counter until the EPROM output exceeds the count. The output of the address counter is then decoded to determine which l.e.d.s are to be lit.

The logic circuit is shown in detail in Figure 3.

The winding 20 of the pick-up is connected to drive two cascaded non-inverting amplifiers 21, 22 the output of the second of which is connected to a peak detector circuit 23. The output of circuit 23 is buffered by a unity gain buffer amplifier 24 and the output of amplifier 24 is reduced by 25% by a potential divider 25. The resulting output is compared with a fixed reference voltage in a voltage comparator 26 and with the output of amplifier 23 in a voltage comparator 27. The outputs of comparators 26 and 27 are combined by an AND gate 28 and it will readily be appreciated that the output of gate 28 will only go high if peak level is above a set value and the actual signal level is more than 75% of the peak level.

The output of gate 28 is applied to the input of a data synchronizer 29 which is clocked at 1MHz by a clock oscillator 30 and the output of the synchronizer 29 is supplied to the clock input of a 5-bit binary counter 31, connected to provide an output pulse for every 15 input pulses from the synchronizer 29. A flip-flop 32 has its CLK input connected to the output of synchronizer 29 and its CLEAR input driven by an OR gate 33 one input of which is connected to the output of counter 31 and the other input of which is connected to a reset pulse generator 34 (which is also connected to a CLEAR terminal of counter 31). The Q output of flip-flop 32 is connected to one input of an AND gate 35, the other input of which is connected via a divide by 2 stage 36 and a divide by 4 stage 37 to the clock 30, so that gate 35 passes pulses at 125KHz for the duration of the periods when the Q output of flip-flop 32 is high (such duration being inversely proportional to the pick-up signal frequency).

The output of gate 35 is connected to the CLK input of a 16-bit binary counter 40, the 16 output terminals of which are connected to respective ones of the 16 'B' input terminals of a 16-bit digital comparator 41. The 'A' input terminals of the comparator 41 are connected to the output terminals of a 16-bit by 2048-word EPROM 42, the address inputs of which are connected to the output terminals of an 11-bit binary counter 43 which is clocked at by the output of the divide by 2 stage 36 under the control of an AND gate 44. This AND gate 44 has an input from the Q output of a D-type flip-flop 45, which has its D input connected to the output of an AND gate 46, its CLK input connected to the clock oscillator 30 and its CLEAR input connected to the reset pulse generator 34. One input of gate 46 is connected to the A>B output of digital comparator 41 and the other to the output of counter 31. The counter 43 has its CLEAR terminal connected to the output of a pulse generator 47 triggered by the output of counter 31. The output terminals of the 11-bit counter 43 are also connected via a decoder circuit 48 to a buffer/l.e.d. driver circuit 49, which has ten outputs driving the various l.e.d.s shown in Figure 1 and 2.

The flip-flop 45 Q output is also connected to the CLK input of another flip-flop circuit 50 which has its CLEAR input connected to the output of reset pulse generator 34 and its Q output connected to the input of the pulse generator 34. The Q output of flip-flop 45 is also connected to a timer circuit 51 which has its output connected to an enable terminal of the buffer/driver 49. Another enable terminal of buffer/driver 49 is connected to a battery voltage sensor circuit 52 so that the buffer/driver 49 is disabled when the battery voltage is low. Sensor circuit 52 also triggers an oscillator 53 when the battery voltage is low, and causes the l.e.d.s 17A and 17B to be flashed (via another buffer/driver 55).

The logic circuit describer operates as follows:-

The counter 31 is clocked by each pulse produced by the gate 28 and during the interval during which the first fourteen pulses are counted the Q output of flip-flop 32 is high, thereby enabling gate 35 and allow 125KHz pulses to be counted into counter 40. The next pulse causes the Q output of flip-flop 32 to go low, thereby inhibiting further counting by counter 40. Furthermore, the output of gate 46 now causes the Q output of flip-flop 45 to go high (the A>B output of comparator 41 being high at this time). This causes gate 44 to start passing pulses to the address counter 43 at 500Kz so that counter 43 counts until the EPROM output is numerically lower than the output of counter 40, at which time the A>B output of the comparator 41 goes low and gate 46 is disabled. Flip-flop 45 changes state and disables gate 44, stopping the address counter. The change-over of flip-flop 45 also triggers the timer 51, triggers the pulse generator 34 and restarts the measuring cycle. The decoder 48 determines which of the l.e.d.s is to be lit in accordance with the count.

The EPROM contents (as shown in Figure 4) are such that when a string is tuned to one of the six required notes both l.e.d.s 17A and 17B are lit and the l.e.d. 14 under the string which should be tuned to that note is also lit. When the l.e.d. under a string which has just been plucked lights, in these circumstances, this signals that the string in question is properly tuned. If the string is sharp the 'sharp' and 'down' l.e.d.s will be lit etc.

Figure 3 also shows an audio frequency oscillator 50 which can be used to produce a reference sinewave at a fixed frequency of, say, 440Hz.

Turning now to the embodiment shown in Figure 5, parts which correspond with parts included in Figure 3 have reference numerals larger than the reference numerals used in Figure 3 by 100, other parts have reference numerals commencing at 201.

Instead of a single pick-up six separate pick-ups 201 to 206 are used and an analogue selector circuit 207 controlled by a central control logic circuit 208 is employed to select which of the pick-ups is connected through to the amplifier 121. The circuit 207 has two further inputs, namely a microphone input and an auxiliary input. In use the logic circuit 208 causes the eight channels of circuit 207 to be enabled cyclically until a signal is detected at the output of comparator 126, indicating that a channel receiving an input has been selected. This channel is then held until a time-out period has expired after loss of the signal at the output of comparator 126.

Instead of the six l.e.d.s 14 of Figure 3, there are seven l.e.d.s 214, representing the seven notes of the C major chord, together with a single "sharp" l.e.d. 215 and two arrow-shaped "up" and "down" l.e.d.s 216, 217. In addition there are five "mode" l.e.d.s 218, 219, 220, 221 and 222.

The control logic circuit 208 has elements performing the same function of some of the logic elements shown in Figure 3. It has, however, more functions than can be obtained with the relatively simple circuit of Figure 3.

The counter 140, the digital comparator 141, the ROM 142, the address counter 143 and the decoder 148 are all 20-bit channel devices instead of the 16-bit channel devices used in Figure 3, to enable addition modes of operation of the tuning device to be implemented.

The control logic circuit 208 receives inputs from a three key mode-selection switch array. Switch 230 is used to select the mode of operation, and its associated logic circuitry operates in well known manner to set a register in the logic circuit 208 and to step the value held in the register for each operation of the switch 230. At power-up, the register is preset to calibration mode in which l.e.d. 218 is lit. In this mode, the other two switches 231 and 232 of the mode selection switch array can be used to change the absolute tuning of the circuit, by varying the divisor input of a frequency divider 233 which is interposed between a clock oscillator 234 and the logic circuit 208. The circuit is arranged to give a 1Hz change at 440Hz for each press of switch 231, 232 (up or down according to which switch is pressed), and, of course, a proportionate change at other frequencies. The l.e.d.s 214, 216, 217 are lit to show the degree to which the tuner has been tuned up or down.

A single press on the mode switch 230 shifts the mode of operation to "guitar" mode, in which l.e.d. 219 is lit. In this mode the circuit operates in the same manner as that described above in respect of Figure 3, except that, the individual l.e.d.s 214 are not lit at all, since the use of the analogue selector 207 and the corresponding control logic in circuit 208 ensures that only the required frequency of the string actually plucked need be tested for. L.e.d.s 216 and 217 indicate the state of tuning of the string plucked, both being lit when the string is correctly tuned.

A second press on the mode switch 230, sets the circuit into microphone mode, with l.e.d. 220 illuminated. In this mode the analogue selector is set to pass input from the microphone input only. The increased size ROM 142 stores data for the entire chromatic scale over a ten octave range and the circuit operates in this mode to light the l.e.d. 214 (with or without l.e.d. 215) indicating the nearest note to that input via the microphone, with either of l.e.d.s 216 or 217 lit to show if the input is slightly sharp or flat relative to the true tuning of the note indicated.

The next press of the mode switch 230 sets the circuit to "output" mode, in which no measurement functions are undertaken but an output signal of any of 120 output frequencies available is output to a socket 240. For this purpose there are provided twelve reference oscillators 241, each tuned to a different note of the chromatic scale in the highest octave. A 1-of-12 selector 242 controlled by the logic circuit 208 selects which one of the oscillators' outputs is passed to the output via a divider 243 and a square-to-sine wave converter 244. When this mode is first entered the logic circuit 208 is set to set selector 242 and divider 243 to pass a default note, e.g. middle C (256Hz) or A (440Hz). Each press of switches 231 or 232 raises or lowers the pitch by one semitone. The note being output is displayed on the l.e.d.s 214, 215.

Another press of switch 230 activates "reference" mode. In this mode, which can operate only if there is a plug in the auxiliary input (the latter having an associated switch connected to the logic to detect this condition) . The frequency of a signal input via the auxiliary input is now compared with a 20-bit data signal stored in a RAM device 250, the RAM device having been selected by a data selector 251 interposed between the ROM 142 and the digital comparator 141. The "up" and "down" l.e.d.s are used to indicate whether the input frequency is higher or lower than the frequency represented by the signal stored in RAM 250.

RAM 250 can be loaded by injecting a signal into the auxiliary input when any mode other than "reference" mode is selected. Insertion of a plug into the auxiliary input socket overrides all these other modes and causes the circuit to enter "store" mode in which causes the count generated in one operating cycle in counter 140 to be loaded into RAM 250 (which should be a non-volatile RAM to ensure that the signal remains stored).

The "reference" and "store" modes are used when it is required to use two or more different tape recorders in recording successive tracks of a multi-track recording. A reference note is recorded using the first tape recorder, this is played back into the tuner circuit using the "store" mode, and is subsequently played back in "reference" mode on the other recorders to enable the speed controls of these other recorders to be matched accurately to the first.

Another press of the mode switch 230 puts the circuit into "basic" mode, in which all the mode l.e.d.s are extinguished. This mode is the same as "microphone" mode, except that it receives input from the pick-ups rather than from the microphone input. It can be used for tuning strings to any required non-standard notes.

Finally, a "chord" mode can be selected by a further press of the mode switch 230. This causes the "cal" and "guitar" l.e.d.s 218, 219 to be lit simultaneously. Now, the mode switch 230 can be held down and the "up" and "down" switches 231, 232 can be used to select the chord required. In this phase of operation the up and down l.e.d.s 216, 217 are used to indicate major or minor and the l.e.d.s 214, 215 are used to indicate the chord selected. Successive presses of the switches 231, 232 cause the selected chord to change through the entire range available, starting for example at a standard chord, say C major.

When the mode switches have been released and a string is plucked, the l.e.d.s 216, 217 indicate whether the string is tuned relative to the tuning required for the appropriate note of the selected chord.

It is to be understood that, although the above described logic circuits have been mentioned as forming part of a tuning aid built into an instrument and using an independent pick-up, its principles are also applicable to a separate instrument which receives its input from the normal pick-up on an instrument or from a microphone.

Many variations are possible within the scope of the present invention, so that tuning aids in accordance with the invention can be provided for electronic keyboard instruments, wind instruments, acoustic stringed instruments and many others. The tuning aid may include its own pick-up or microphone, but need not necessarily do so. It may also include its own power source, but, again, this is not essential.

Claims

1. A tuning aid for a stringed instrument comprising input circuit means for receiving an oscillatory electrical signal from the instrument to be tuned, conversion means for deriving a first multibit digital signal dependent on the frequency of said signal, reference frequency means for successively producing a plurality of reference multibit digital signals representing reference frequencies, digital comparator means for comparing said first multibit digital signal with said reference multibit digital signals in turn, and display means controlled by said comparator means for indicating the relationship between said frequency and said reference frequencies.

2. A tuning aid as claimed in claim 1 in which said display means comprises first and second display devices indicating respectively when said frequency is above or below a selected one of said reference frequencies.

3. A tuning aid as claimed in claim 1 in which said reference frequency means comprises a memory device and an address counter, said memory device being programmed at different addresses with data corresponding to a plurality of different frequencies, the outputs of the memory device being connected to one set of inputs of the digital comparator means, and control means being provided for said address counter which operates to step the address counter until a change in state of an output of the digital comparator means is detected by the control means.

4. A tuning aid as claimed in claim 3 in which said memory device is a read-only memory device, preprogrammed with said data.

5. A tuning aid as claimed in claim 1 in which said conversion means comprises first counter means for counting a predetermined number of cycles of said oscillatory electrical signal, enabling means connected to said first counter means, and a second counter means connected to said enabling means and to a clock pulse source, said second counter means counting the number of pulses received from said clock pulse source during the time taken for the first counter to count said predetermined number of cycles.

6. A tuning aid as claimed in claim 1 in which said display means comprises a plurality of display devices representing different frequencies respectively, decoder means being provided for activating an appropriate one of said display devices when said oscillatory electrical signal is tuned to that frequency.

7. A tuning aid as claimed in claim 6 in which said display devices correspond respectively to standard guitar open-string frequencies.

8. A tuning aid as claimed in claim 6 in which said display devices correspond respectively to the notes of the C major scale, an additional display device being provided to indicate when the oscillatory electrical signal is tuned to a frequency differing from one of the notes of the C major scale by a semitone.

9. A tuning aid as claimed in claim 1 further comprising a pick-up device arranged to detect vibration of a string of the instrument and generate said oscillatory electrical signal.

10. A tuning aid as claimed in claim 9 in which said pick-up device comprises a plurality of pole pieces associated respectively with the strings of the instrument, and a single winding in which said oscillatory electrical signal is induced, irrespective of which string is plucked.

11. A tuning aid as claimed in claim 9 in which said pick-up device incorporates a plurality of windings associated with respective strings of the instrument, an analogue signal selector circuit being provided by means of which only the oscillatory signal from the winding of a string which is vibrating is passed to said conversion means.

12. A tuning aid as claimed in claim 1 further comprising battery voltage detection means connected to said display means and operating to activate said display means to indicate the fall of the battery voltage below a set level.

13. A tuning aid as claimed in claim 1 including means for providing an output reference frequency signal to a socket on the tuning aid.

14. A tuning aid as claimed in claim 13 in which said output reference frequency signal is a fixed frequency signal.

15. A tuning aid as claimed in claim 13 in which a plurality of reference frequency oscillators isprovided, said oscillators operating at frequencies corresponding to the note of a chromatic scale, and a selector being provided for selecting which one of the oscillators provides the output.

16. A tuning aid as claimed in claim 15 in which there is further provided a frequency divider connected between said selector and the output socket, said frequency divider being adjustable to divide the selected oscillator frequency to reduce the output frequency by a selected number of octaves.

17. A stringed instrument having a tuning aid, said tuning aid comprising a pick-up sensitive to vibrations of the instrument's strings and producing an oscillatory electrical signal of frequency dependent on such vibrations, logic circuit means connected to said pick-up to receive signals therefrom and display means connected to logic circuit means and arranged to indicate when a string is vibrating at a frequency appropriate to that string.

18. A stringed instrument as claimed in claim 17 in which said display means comprises a plurality of display devices associated respectively with the strings of the instrument, said logic circuit means activating a particular one of such display devices when the oscillatory electrical signal frequency is at or near the frequency appropriate to the associated string, and a plurality of further display devices, said logic circuit means activating said further display devices in accordance with the frequency relationship between the frequency of said oscillatory electrical signal and the appropriate frequency.

19. A stringed instrument as claimed in claim 18 in which said plurality of display devices are disposed in an underlying relationship with the respective associated strings.

20. A stringed instrument as claimed in claim 19 in which the tuning aid has a row of pole pieces forming part of said pick-up, said display devices being arranged in a spaced, parallel row, and the further display devices being arranged in a group separate from said row of display devices.

21. A stringed instrument as claimed in claim 17 in which the logic circuit means includes conversion means for converting said oscillatory electrical signal into a first multibit digital signal, reference frequency means for successively producing a plurality of reference multibit signals representing reference frequencies and digital comparator means for comparing said first multibit digital signal with said reference multibit digital signals in turn, said display means being controlled by said comparator means.