Electronic music system and stringed instrument input device therefor2010-03-02 00:00:00with OP and produces an output signal only when NP is greater than or equal to OP.
The second condition tested by NP tester 40 is whether NP is greater than the highest valued offset voltage provided by the offset voltage source 28. The reason for this test is that when all of the strings of the guitar are open, the systemsamples only zero voltages on all of the strings and will produce during each sampling cycle an NP signal equal to the highest offset voltage, of 2.4 volts. This voltage does not represent a desired tone and, therefore, should not be transmitted to thesynthesizer.
The parts of the NP tester 40 used to test whether NP is greater than the highest offset voltage consists of a comparing operational amplifier 84 having NP supplied to its non-inverting terminal and a reference voltage supplied to itsnon-inverting terminal which reference voltage is greater than the highest offset voltage and less than the lowest fret voltage, the reference voltage in the illustrated case being taken to be 4.0 volts. Thus, it will be understood that when a string ispressed against a fret NP will be greater than the 4.0 volt reference voltage to produce a high output from the amplifier 84. Oppositely, when no string is pressed against a fret NP will be equal to the highest offset voltage of 2.4 volts, which is lessthan the 4.0 volt reference, to cause the output from the amplifier 84 to be low.
The outputs of the two test amplifiers 78 and 84 are connected to one another and to an output line 86 by two diodes 88, 88, as shown, to provide an AND gate circuit whereby a high or OK signal appears on the output line 86 only when the outputsfrom the two amplifiers 78 and 84 are high, thereby indicating that both conditions tested by the NP tester are satisfied. The OK signal appearing on the output line 86 is in turn transmitted through an AND gate 90, when enabled by control signal T1, tothe sample and hold circuit 42.
Before leaving the NP tester 40, it should also be noted that NP has a value greater than the highest offset voltage when at least one of the strings of the guitar is pressed against a fret. Therefore, the output of the amplifier 84 is anindication of whether or not a string is pressed into contact with a fret. When the output of the amplifier 84 is high it constitutes a string down or SD signal which is transmitted to the flip-flop 45 to indicate the string down condition.
The sample and hold circuit 42 includes a memory or holding capacitor 92 to which NP is transferred from the cycle peak detector 38 through a transfer gate TGD controlled by the illustrated TRAN signal provided by the AND gate 90. The voltageappearing on the storage capacitor 92 is in turn supplied by a voltage follower operational amplifier, preferably having dual FET input terminals as shown, to the line 96 for transmission to the synthesizer 10 as the input signal thereto.
As mentioned, the synthesizer 10 may be of any well known construction and basically is a tone generator for producing an output audio frequency signal having a fundamental frequency controlled in response to the voltage level of the inputvoltage signal. By way of illustration, the synthesizer 10 in FIG. 2 is shown in more detail to include an
exponential amplifier 98 to which the input signal appearing on the line 96 is applied. The input signals appearing on the line 96 vary linearlywith tone values as measured by musical intervals between the tones. That is, the input signal, for example, increases by 100 mv. for each semi-tone increase in musical tone value. The frequencies of the tones, however, vary
exponentially with changesin tone values, and amplifier 98 amplifies the incoming voltage signal by a gain varying
exponentially with input voltage to produce an output signal therefrom directly related in voltage level to the desired output tone frequency.
The signal provided by the
exponential amplifier 98 is in turn supplied to a voltage controlled oscillator 100. The output of the voltage contr...
Electronic musical instrument with exponential keyboard and voltage controlled oscillator2010-02-26 00:00:00voltage, from an
exponential voltage divider, for controlling the frequency of a voltage controlled oscillator, which produces a frequency which is directly proportional to the control voltage and inversely proportional to a reference voltage. The reference voltage compensates for variations in the level of the supply voltage, so that the oscillator frequency is independent of the supply voltage.ClaimsWhat is claimed is:
1. An electronic musical instrument having a voltage controlled oscillator for producing a sound signal having a frequency proportional to a control voltage applied to it, akeyboard having a plurality of keys, a plurality of switches, one for each of said keys, each adapted to be operated by depression of its associated key, and a voltage divider connected with said switches for connecting a control voltage to saidoscillator which corresponds to the position of the key associated with an operated one of said switches, said voltage divider comprising a plurality of resistance elements connected in series, each of said elements having different resistance valueswhich bear an
exponential relation to the resistance values of the adjacent connected resistors such that the voltage at successive junctions of said resistance elements correspond to a geometric series, said resistance elements being formed of the samematerial and being physically located in close physical juxtaposition with each other, so that all said resistors are maintained at approximately the same temperature, with approximately constant relative resistances.
2. Apparatus according to claim 1 wherein said resistance elements are formed simultaneously as portions of a single integrated thick-film circuit.
3. In an electronic musical instrument having an electrical power supply, a voltage controlled oscillator for producing a sound signal having a frequency proportional to a control voltage applied to it, a keyboard having a plurality of keys, aplurality of switches, one for each of said keys, each adapted to be operated by depression of its associated key, and connecting means connected with said switches for connecting a control voltage to said oscillator which corresponds to the position ofthe key associated with an operated one of said switches, the combination comprising a reference voltage generator connected to said electrical power supply for producing a reference voltage, and means connecting said oscillator to said reference voltagegenerator, said reference voltage generator being adapted to produce a shift in the level of said reference voltage in response to a change in the level of voltage of said electrical power supply, said shift having a magnitude and direction tending tocompensate for said change in power supply voltage level, whereby said oscillator frequency is substantially independent of said change.
4. Apparatus according to claim 3, wherein said reference voltage generator comprises an inverter having an input connected with said power supply.
5. Apparatus according to claim 4, wherein said oscillator comprises an integrator for integrating a voltage derived from said voltage divider, a comparator connected to said integrator and operative to compare an output produced by saidintegrator with said reference voltage, and means connected with said comparator and operative upon a comparison of said integrator output and said reference voltage for resetting said integrator for a subsequent cycle of integration.
6. An electronic musical instrument having a voltage controlled oscillator for producing a sound signal having a frequency proportional to a control voltage applied to it, a keyboard having a plurality of keys, a plurality of switches, one foreach of said keys, each adapted to be operated by depression of its associated key, a voltage divider connected with said switches for connecting a control voltage to said oscillator which corresponds to the position of the key associated with anoperated one of said switches, said voltage divider comprising a plurality of resistance elements connected in series, each of said elements having resistance values which bear an
exponential relation to the resistance values of adjacent connectedresistors such that the voltage...
