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Description  |
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BACKGROUND OF THE INVENTION
This relation relates to the field of electronic musical instruments and,
more particularly, to a musical instrument responsive to an analog signal.
The analog signal may be generated in response to the reception of energy
within the audible range.
Electronic organs usually have a plurality of operator-selectable tone
generators capable of providing musical sounds, as clarinets, flutes,
oboes, drums, violins, etc. These electronic instruments usually include
decoding circuitry for decoding various notes and octaves. The decoding
circuitry is responsive to the operator-controlled switches, the stops and
the keyboard.
We have developed a musical instrument similar to an electronic organ, but
rather than being responsive to operator-controlled switches and a
keyboard, our instrument is responsive to audible energy imparted to a
microphone by the operator.
SUMMARY OF THE INVENTION
A microphone is coupled to a frequency multiplier which provides a signal
to a phase locked loop to generate an analog voltage proportioal to the
frequency of the audible energy imparted to the microphone. The analog
voltage is applied to a gate signal generator wherein the signal is
converted to a succession of digital words. The digital words are decoded
to provide octave and note of scale information which then gates selected
tone generators.
It is a feature of the present invention to provide an analog signal
responsive to audible energy for controlling an electronic musical
instrument.
It is a feature of the present invention to provide a gate signal generator
having an octave and note of scale decoder which is responsive to an
analog signal.
Yet another feature of the invention is to provide an electronic musical
instrument wherein the developed tone gating signals are responsive to
audible energy imparted to a microphone.
Yet a further feature of the present invention is to provide a simplified
gate signal generator that provides octave and note decoding with a
minimum of parts.
Other features of the invention will become apparent when considering the
specification in combination with the drawing in which:
DRAWING
FIGS. 1A and 1B are block diagrams of the musical instrument;
FIG. 2 is a schematic diagram of the octave decoder shown in FIG. 1B; and
FIG. 3 is a schematic diagram of the note of scale decoder shown in FIG. 1B
.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to FIGS. 1A and 1B, electronic musical instrument 10 is shown.
The operator of the instrument speaks, sings or hums into microphone 12 to
produce an analog voltage 14, the amplitude being proportional to the
frequency of the audible energy provided to microphone 12. The amplitude
of the audible energy at microphone 12 is represented by the signal from
level output 16.
The analog voltage 14 is connected to gate signal generator 18 which
provides octave and tone gate signals for the frequency represented by the
amplitude of the analog voltage 14. The gate signals generated are applied
to the analog gates 20 which gate the outputs of the plurality of tone
generators 22 to provide a corresponding tone responsive to the amplitude
of the analog signal 14. The tones are provided to level set circuit 24.
The amplitude of the tones on the output of the level set circuit 24 is
proportional to the amplitude of the level output 16. Amplifier 26
amplifies the tones from level set circuit 24 and provides the amplified
signal to speaker 28. Depending upon the harmonic content of the tones
produced by tone generator 22, musical instrument 10 may have a variety of
different musical sounds, as a clarinet, flute, oboe, drum, violin, etc.
Irrespective of the tones produced, the output from speaker 28 is
proportional to the frequency and the amplitude of the audible energy
imparted to microphone 12.
Microphone 12 is responsive to energy having a frequency between
approximately 100 and 1600 Hz. The output of microphone 12 is coupled to
amplifier 30 which provides amplification of the signal within the audible
range. The output of amplifier 30 is provided to a band pass filter 32
which removes all frequencies less than 100 Hz and greater than 1600 Hz.
The signal from band pass filter 32 is applied to a full wave rectifier
34. The full wave rectifier rectifies the signal from band pass filter 32
into a signal having a single polarity. The output of the full wave
rectifier 34 is applied to low pass filter 36 which removes all high
frequencies generated as a result of the rectification. The output of
filter 36 is a voltage having an amplitude which varies in accordance with
the energy imparted to microphone 12. The output of the full wave
rectifier 34 is also provided to frequency multiplier 38. The frequency
multiplier 38 multiplies the frequency of the input signal by an integer
N, as 2. Frequency multiplier 38 speeds up the response time of the
circuit. The signal from the frequency multiplier 38 is applied to phase
detector 40. Frequency multiplier 38 is also coupled to low pass filter
36. The frequency multiplier 38 is not operative unless the signal from
full wave rectifier 34 exceeds a threshold voltage established by the
variable resistor 42. Thus, the audible energy to microphone 12 must be
sufficiently great to overcome the threshold voltage determined by
variable resistor 42, as set by the operator.
The frequency of the signal from frequency multiplier 38 determines the
amplitude of analog output 14. Phase detector 40 compares the frequency
from frequency multiplier 38 to a phase locked loop frequency on line 44.
The difference in frequencies is represented by an analog voltage provided
on output line 46. The analog voltage on line 46 is provided to an
augmenting integrator 48 which amplifies and integrates the signal on line
46 to provide analog output 14 at its output 50. To provide the phase
locked loop voltage on line 44, the analog voltage 14 is coupled to a
voltage-controlled oscillator 52, nominally 4 KHz, which generates a
signal on line 54, the frequency of which is dependent upon the amplitude
of the analog output 14. Specifically, when there is no difference between
the frequency of the signal from multiplier 38 and the frequency of the
signal on line 44 (i.e., the input of augmenting integrator 48 is zero),
the frequency of the signal on line 54 is a whole number multiple of the
frequency from frequency multiplier 38. The signal on line 54 is provided
to frequency divider 56. The frequency divider 56 divides the whole number
signal on line 54 by a fixed value. Thus, the voltage from analog output
14 follows or "tracks" the frequency from frequency multiplier 38.
Auxiliary outputs 58 are also provided from frequency divider 56. Each
auxiliary output signal represents a whole number division of the input
frequency and may be used in a manner which will become apparent below.
The analog voltage 14 varies between 0 and approximately 10 volts,
representing a frequency of approximately 100-1600 Hz. A/D converter 60 is
clocked by clock 62 and generates 8-bit words representative of the
amplitude of the analog signal. As is characteristic of most A/D
converters, A/D converter 60 provides a succession of 8-bit words each of
which is shifted to the right one position when the analog voltage input
is divided in half. Thus, if the 8-bit word 10000000 represents 10 volts,
the 8-bit word 01000000 represents 5 volts and the word 00100000
represents 2.5 volts.
Octave and frequency have a similar relationship in that the frequency of a
note in the musical scale in one octave is exactly twice the frequency of
the same note in the next lower octave.
The three most significant bits of each 8-bit word provide octave
information of the signal imparted to microphone 12, and the note within
the octave is available from the entire 8-bit word, as will be explained
in greater detail below.
Octave decoder 64 determines which one of three octaves each 8-bit word
represents. Octave information is provided to analog gates 20 by line 66
from octave decoder 64. Octave decoder 64 also provides a five-position
window which acquires a binary code representing the note in the musical
scale. The window selects five of the eight bits and the five bits that
are selected depend on which octave has been decoded. The signals from the
window are provided to note of scale decoder 68 by line 70 and convert the
5-bit code from the octave decoder to a 12-bit code representative of each
note in the musical scale. The signals representing the notes are applied
to analog gate 20 and control the gates in the well known manner. Analog
gates 20 gate the signals from the tone generator 22 in the well known
manner.
Referring to FIG. 2, the operation of octave decoder 64 will now be
described. During the description it is helpful to recall that a binary
word, as 10001000, which represents a note in one octave, will be shifted
one place to the right (i.e., 01000100, and will represent the same note
in the next lower octave since the analog voltage representing the latter
note is half that of the former. The six NAND gates in the octave logic
circuit 70 provide 3-bit words 001, 010 and 100, indicative of octaves I,
II and III, respectively. Although the octave logic circuit is shown to
provide only three octaves, a greater number of octaves may be provided by
increasing the word size from A/D converter 60 or providing for a more
complex decoding circuitry. Comparators 72, 74, 76, 78 and 80 provide the
five-position window which acquires note information and provides that
information to lines a, b, c, d and e (and their inverted signals). The
five comparators are analogous to a five-pole, three-position switch that
selects: bits 4-8 and provides information regarding those bits to lines
a-e for octave I; bits 3-7 and provides information regarding those bits
to lines a-e for octave II; bits 2-6 and provides information to lines a-e
for octave III. Thus, lines a-e and lines a-e always contain information
regarding a note in the musical scale irrespective of the octave
information provided by the three most significant bits.
Similarly constructed comparators 72, 74, 76, 78 and 80 are best understood
by considering the operation of comparator 72. NAND gates 84, 86 and 88
are provided with octave I, II and III information. Depending upon the
octave represented, a single one will be provided to one of the NAND
gates. The NAND gate receiving the one is enabled, and the output a and a
represent the state of the bit coupled to the enabled NAND gate. Thus, if
bit 2 were one, indicating octave II, NAND gate 86 would be enabled,
providing bit 3 information to a and a.
Referring to FIG. 3, the information from lines a-e and a-e is provided to
note of scale decoder 68. The note of scale decoder translates the a-e and
the a-e information from octave decoder 64 into signals for switching the
twelve notes of each scale. Although any particular decoding scheme can be
employed to accomplish the translation, the decoding scheme provided by
NAND gates 89-105 and their corresponding interconnection between lines
a-e and a-e provide a simplified method of decoding. The outputs of NAND
gates 90, 91, 96, 97 and 100-104 are coupled through inverters 106, 107,
110, 111 and 113-117, respectively. NAND gates 92 and 93, 94 and 95 and 98
and 99 are each coupled together by NAND gates 108, 109 and 112,
respectively. The decoding sequence of NAND gates 90-104 is shown by the
binary notation within the gate. For example, referring to NAND gate 94, a
code of 11001 provides an output pulse from NAND gate 94. Referring to
NAND gate 96, an output pulse is provided for the input signal of 1011 as
well as 1000.
Signals representing each of the twelve notes of the musical scale are
provided for NAND gates 106 and 107 and may be applied to any well known
analog gate circuit. The information regarding the note of scale is
combined with the octave information by analog gate 20 to gate the tones
from the tone generator 22.
The construction of other embodiments will be apparent. For example, the
auxiliary outputs 58 of FIG. 1A could be combined in well known stop
switches (not shown) and then provided to filters and audio amplification
systems. In this case, analog voltage 14 would not be used, and unusual
musical tones could be provided.
Finally, the electronic musical instrument may be operated as above or as
an accompaniment to a well known electronic organ.
* * * * *
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