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| United States Patent |
5,029,510
|
|
Elion
|
July 9, 1991
|
Guitar control system
Abstract
A guitar control system using multiple string processing channels for
developing pitch and peak signals for a multiple of string vibrations.
Pitch data is multiplexed into a microprocessor along with the peak data
and the programmed microprocessor outputs processed sound information on
an address/data buss. Midi input/output, analog input/output and counter
circuitry are interactively connected with the data buss, and final audio
processing is derived from the analog output.
| Inventors:
|
Elion; Clifford S. (Van Nuys, CA)
|
| Assignee:
|
Gibson Guitar Corp. (Nashville, TN)
|
| Appl. No.:
|
467490 |
| Filed:
|
January 19, 1990 |
| Intern'l Class: |
G01H 003/18 |
| Field of Search: |
84/723,725,726,728,735-738,743,645,DIG. 9,742
|
References Cited
U.S. Patent Documents
| 4748887 | Jun., 1988 | Marshall | 84/646.
|
| 4817484 | Apr., 1989 | Iba et al. | 84/726.
|
| 4841827 | Jun., 1989 | Uchiyama | 84/622.
|
Primary Examiner: Shoop, Jr.; William M.
Assistant Examiner: Donels; J.
Attorney, Agent or Firm: Laney, Dougherty, Hessin & Beavers
Claims
What is claimed is:
1. A guitar control system comprising:
a multi-phonic string vibration pickup providing respective string outputs;
a plurality of string processing channels with harmonic rejection filter
each receiving input of a respective string output and each generating a
pitch output and a peak output;
input multiplexing means receiving each of said pitch outputs and providing
a multiplexed output;
a programmed microprocessor receiving input of said multiplexed output and
each of said peak outputs, and providing output of string related data on
an address/data buss;
a midi interface connected to said buss for converting string related data
for synthesizer input;
an analog input/output circuit connected to said buss;
a counter circuit connected to said buss and generating a filter output for
each string, with each filter output being conducted back to the
respective string processing channel for input to the respective harmonic
rejection filter; and
audio processing circuitry receiving output from said analog input/output
circuit and providing selected audio output.
2. A guitar control system as set forth in claim 1 wherein each of said
string processing channels is further characterized to include:
an input buffer and anti-aliasing filter receiving said input and
generating a first filtered output for input to said harmonic rejection
filter; and
a reconstruction filter receiving input from said harmonic rejection filter
and providing an output.
3. A guitar control system as set forth in claim 2 which is further
characterized to include:
a negative peak detector receiving said reconstruction filter output to
provide a negative peak output; and
a positive peak detector receiving said reconstruction filter output to
provide a positive peak output.
4. A guitar control system as set forth in claim 2 which is further
characterized to include:
a positive peak track/hold circuit receiving said reconstruction filter
output and generating a peak signal for input to said microprocessor.
5. A guitar control system as set forth in claim 3 which is further
characterized to include:
differentiating means receiving said negative peak output and generating a
pitch plus signal;
second differentiating means receiving said positive peak output and
generating a pitch minus signal; and
means for applying the pitch plus and pitch minus signals as inputs to said
input multiplexing means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to guitar/MIDI type systems and, more
particularly, but not by way of limitation, it relates to improved guitar
synthesis systems having greater versatility and feel.
2. Description of the Prior Art
There is a great amount of recent prior art that relates to the playing of
various musical instruments through a MIDI-musical instrument digital
interface system wherein an instrument signal is derived, digitized and
sound synthesized to produce an audio output. Various forms of effects may
be mixed with the final output sound. There have been various types of
guitar controllers developed in recent years; however, there are two basic
types of guitar controllers that find wide commercial application. A first
type is that which determines the pitch from the waveform of the guitar
output. The second is a type which utilizes some other parameter to
represent the pitch, i.e., usually the length of the string.
The first category usually makes use of a special pickup which is mounted
on a normal guitar, as is the case in the present invention. It is deemed
important to retain the "guitarness" or "feel" of the instrument and a
retrofittable hexaphonic magnetic pickup is utilized with such a pitch
detection system. A second category almost always requires that the
instrument is a somewhat altered guitar The guitar may have all strings of
one gauge, or the neck may be wired so that there are electrical contacts
on each fret, etc. Still other types of guitar source utilize sensors
connected to the individual strings or other obstructions that compromise
the visceral nature of playing the guitar.
SUMMARY OF THE INVENTION
The present invention includes a plurality of string processing channels
for determining the pitch and the peak characteristics, one processing
channel for each string of the guitar The pitch signals are applied in
parallel to an input multiplexing logic which prepares each of the pitch
signals for input to a microprocessor or microcontroller, and the
plurality of string peak signals are also applied as input to the
microprocessor. The microprocessor then functions to process output data
on a parallel buss supplied to each of a MIDI input/output, an analog
input/output and a counter. The MIDI circuitry then deals with the
external synthesizer and other effects circuitry. The analog input/output
provides a data output to audio processing circuitry and the counter
circuitry develops a string filter timing count for return back to the
string processing channels.
Therefore, it is an object of the present invention to provide a guitar
signal controller suitable for use with any MIDI-equipped synthesizer.
It is also an object of the invention to provide a guitar sound controller
that retains the guitarness and feel for playing the instrument.
It is still further an object of the present invention to provide a more
versatile interface that allows the user to control synthesizer and
effected guitar sounds from a single location.
It is yet another object of the invention to provide an improved method for
measuring as many as twelve simultaneous pitch periods.
Finally, it is an object of the present invention to provide a new level of
control for the guitar player wherein an effects loop controller can be
integrated with the MIDI converter hardware and control interface.
Other objects and advantages of the invention will be evident from the
following detailed description when read in conjunction with the
accompanying drawings which illustrate the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the guitar control system;
FIG. 2A is a schematic diagram of a first part of the string channel peak
detection circuitry;
FIG. 2B is the second part of the peak detection circuitry;
FIGS. 3A, 3B and 3C are a schematic diagram of the microprocessor control
section;
FIG. 4 is a schematic diagram of a high-speed input multiplexing circuit of
the invention;
FIG. 5 is a schematic diagram of the memory address decoding and weight
state generator circuitry; and
FIG. 6 is a schematic diagram of the pulse width modulation smoothing
filter and voltage control track and hold circuitry of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The guitar control system 10 includes a plurality of string processing
channels 12, one channel for each guitar string. In the present
discussion, six guitar strings are utilized and these are designated
herein as HE (high end), B, G, D, A and LE (low end). Each of the string
processing channels derived both a pitch output for input to input
multiplexing logic circuitry 14, and they derive a peak output for input
to a microcontroller 16.
The microcontroller 16 communicates by means of busses 18 and 20 with a
parallel array of circuitry. The MIDI input/output circuitry 22 provides
the interface to the synthesis equipment wherein the music or tone
selective sound is generated, and an analog input/output array 24 provides
output connection to the final audio processing circuitry. A counter
circuit 28 provides a plurality of string channel filter outputs 30 and
these are fed back via line 32 for input to the individual string
processing channels wherein they function as a clock controller, as will
be further described. The microcontroller 16 also provides string channel
reset pulses 34.
Referring now to FIG. 2A, guitar string input is applied at input terminal
36 for input to a buffer and filter amplifier 38, IC-type TL072P. The
input to terminal 36 is derived from a hexaphonic magnetic pickup mounted
on the guitar controller. Thus, there is a pickup adapted to transmit the
characteristic acoustic signal for each of the strings LE through HE, and
each of these string inputs is separately applied to its own individual
string processing channel such as that of FIGS. 2A and 2B.
String input at terminal 36 is then applied to the filter amplifier 38
which functions as an input buffer and an antialiasing filter. Output from
filter amplifier 38 is then applied via lead 40 to a harmonic rejection
filter 42. The harmonic rejection filter 42 consists of a type XR1003CP
integrated circuit 44 that receives the output on lead 40 at pin 8, and a
filter clock input at pin 2 thereby to provide a filtered output at pin 5.
The filter clock is derived for the respective string channel in counter
28 as previously described (FIG. 1).
Output from the harmonic rejection filter 42 is then coupled through
junction 46 to a reconstruction filter amplifier 48, another section of an
IC-type TLO72P. Output from reconstruction filter 48 is via line 50 to a
negative peak detector 52, IC-type 4LM1458N. A negative peak signal output
is then present on a lead 54.
Referring now to FIG. 2B, the peak signal on lead 54 is coupled through a
capacitor 56 whereupon a PITCH PLUS signal is present on a lead 57 and the
signal is also applied to the CLEAR input of a FLIP FLOP 58, a peak
de-glitcher, IC-type 74C74N. A SET pulse on Q output 60 provides the
de-glitching function.
Referring also to FIG. 2A, a second output lead 62 from filter amplifier 48
is applied in FIG. 2B to both a positive peak track/hold circuit 64 and a
positive peak detector 66. The positive peak detector 66, a section of
IC-type 4LM1458N, provides output to an inverter 68 to lead 70 as the
PITCH MINUS signal. The PITCH MINUS signal on lead 70 is passed through
another inverter 72 for input to the CP terminal of FLIP FLOP 58 as well
as to the track/hold circuit 64 at logic input pin 8. The track/hold
circuit 64 is an IC-type LF398N which receives input from lead 62 at pin
3, the logic input from lead 70 at pin 8, reference input at pin 7 and it
provides a PEAK output on lead 74.
FIGS. 3A and 3B illustrate the system central processing unit as it is
based upon a microprocessor 80, an INTEL type 80C196 integrated circuit.
The central processing unit (FIGS. 3A and 3B) handles all front panel
controls, MIDI communications, pitch conversion and includes a proprietary
1/2 duplex serial communications link for communications with the foot
controller (not shown). Therefore are also many allowances for future
product expansion. The microprocessor 80 communicates with the AD
(Address/Data) buss 82 for interconnection with each of data RAMS 84 and
86, IC types 62LP64-15, and address latches 88 and 90, IC types 74AC373N.
The AD buss 82 is also connected to a pair of program EPROMS 92 and 94, IC
types 27C255-20, and on FIG. 3C the AD buss 82 connects to a pair of
filter control counters 96 and 98, IC types 82C54. A BA buss 100 provides
interactive connection between the EPROMS 92, 94 and the data RAMS 84, 86
and address latches 88, 90. Finally, the AD buss 82 provides eight-lead
connection 102 to a serial interface 104 (see FIG. 3B), an IC type
SCN2681AC1N28.
The program for the microprocessor 80 resides in 32K bytes of EPROM
residing in EPROMS 92 and 94 and configured as 16K bytes of 16-bit program
memory and 32K bytes of static RAM. The memory map is as follows:
______________________________________
Memory Map
Address Description Buswidth WaitStates
______________________________________
OFFFFH
Program &
Data RAM 0 1
08000H
07FFFH
Program
EPROM 1 1
02000H
01FFFH
I/O 0 3
See I/O Map
00100H
000FFH
Monitor NMI
Routine 0 1
00000H
I/O ADDRESSING
01120H - 01123H
Display 0 3
01124H - 01127H
Peakset 0 3
01128H - 0112BH
FxSwitch 0 3
0112CH - 0112FH
VcaMux 0 3
01130H - 01133H
Count1 0 3
01134H - 01137H
Count1 0 3
01138H TestPort1 0 3
0113CH TestPort2 0 3
01140H - 01143H
DUART 0 3
______________________________________
A portion of AD buss 82 is also applied to peak READ-BACK buffer circuits
106 and 108, IC types 74HC.sub.244 N. The port P0 inputs to microprocessor
80 are from the individual string peak signals as derived on lead 74 of
FIG. 2B. Such a peak signal on a lead 74 is developed for each of guitar
strings HE through LE and each such signal is applied to a selected one of
ports P0 of microprocessor 80. The OL1-4 signals as applied to the HSI
inputs of microprocessor 80 are developed in the high speed input
multiplexer, as will be further described below.
Referring now to FIG. 4, there is illustrated the high speed input
multiplexer 14 (FIG. 1). The high speed multiplexer 14 receives PITCH+ and
PITCH- for input for each of guitar strings HE-LE and each is conducted
through an inverting gate 110a-f (IC types 74C132N). An inverted PITCH
SIGNAL is then applied to respective pairs of FLIP FLOPS 112a-f and 114a-f
with respective outputs being applied to the inputs of an EPLD multiplex
stage 116, IC type 22V10DC. The multiplexer 116 is programmed with the
multiplexing logic as it divides the 6 Mhz clockout from microprocessor 80
into two phases 180.degree. apart, CYCLE A and CYCLE B. Each cycle is
synchronous with the processor 80 sampling the high speed input (HSI) unit
as each cycle occurs once every sixteen "state" times. The EPLD
multiplexer 116 outputs four bits of data, CYCLE A, L2, L3, L4, to a latch
circuit 118a through 118d. The latched outputs from latches 118, type
74C174N FLIP FLOPS, are the respective pulses OL1-OL4 on the rising edge
of CLOCK B from EPLD 116 for presentation to the HSI unit of
microprocessor 80.
The upper three bits OL2, OL3 and OL4 represent peaks from the peak
detectors (FIG. 2B). That is, HIE, B, G during CYCLE A and D, A, LE during
CYCLE B, and the first bit OL1 represents the cycle, a high level for
CYCLE A and a low level for CYCLE B. The input multiplexing logic is
designed so that if no new edges occur on the input data, then no new
events are presented to the microprocessor 80. The time between the
positive and negative peaks can thus be measured, and subsequently the
pitch of the incoming note and the MIDI note number can be determined. The
HSI events are recorded by the microprocessor 80 in an 8-level deep,
20-bit wide FIFO. The FIFO contains the status of OL1, OL2, OL3 and OL4 at
the occurrence of the event as well as at the time of the event. When
microprocessor 80 services the HSI interrupt, it uses the storage status
information to determine which guitar string caused the interrupt, and the
peak status latch is then read to determine the polarity of the peak. The
pitch period is then calculated from the difference between the time of
this peak and the time of the previous peak of the same polarity. If that
peak is positive, then the processor reads the amplitude presented to it
by the track/hold stage 64 (FIG. 2B).
The program for the 6-to-4 high speed multiplexer 116 is as follows:
______________________________________
/** Inputs **/
Pin 1 = 6MHZ ; /*REGISTER CLOCK*/
Pin 2 = A1H ; /* */
Pin 3 = A1L ; /* */
Pin 4 = A2H ; /* */
Pin 5 = A2L ; /* */
Pin 6 = A3H ; /* */
Pin 7 = A3L ; /* */
Pin 8 = B1H ; /* */
Pin 9 = B1L
Pin 10
= B2H
Pin 11
= B2L
Pin 13
= B3H
Pin 14
= B3L
Pin 15
= BRESET
/** Outputs **/
Pin 16
= L1 ; /* */
Pin 17
= L2 ; /* */
Pin 18
= L3 ; /* */
Pin 19
= L4 ; /* */
Pin 20
= CYCLEA ; /* */
Pin 21
= CLKA ; /* */
Pin 22
= Q1 ; /* */
Pin 23
= Q2 ;
/** Declarations and Intermediate Variable Definitions
**/
/*
* The inputs A1L and A1H are separated by a 6 Mhz
*
* clock cycle.
* .fwdarw. !A1L & A1H pulses at the +ve going edge of
*1L
* This version of the algorithm thus gives channel
*
* requests on positive going edges of the input
*
*/
CHA1.sub.-- REQ = (!A1H & A1L);
CHB1.sub.-- REQ = (!B1H & B1L);
CHA2.sub.-- REQ = (!A2H & A2L);
CHB2.sub.-- REQ = (!B2H & B2L);
CHA3.sub.-- REQ = (!B3H & B3L);
CHA.sub.-- REQ = (CHA1.sub.-- REQ # CHA2.sub.-- REQ # CHA3.sub.-- REQ);
/** Logic Equations
**/
PRESET.OE = `B`0;
B3L.OE = `B`0;
Q1.SP = `B`0;
Q1.AR = `B`0;
Q1.OE = `B`1;
Q2.SP = `B`0;
Q2.AR = `B`0;
Q2.OE = `B`1;
CLKA.SP = `B`0;
CLKA.AR = `B`0;
CLKA.OE = `B`1;
CYCLEA.OE = `B` 1;
CYCLEA.AR = `B`0;
CYCLEA.SP = `B`0;
Q1.D = !(Q1);
Q2.D = ((Q1 & !Q2) # (!Q1 & Q2));
CLKA.D = ((!Q2 & CLKA) # (!Q1 & CLKA) # (Q1 &
!CLKA & Q2));
CYCLEA.D = ((!CLKA & CYCLEA) # (!Q2 & CYCLEA)
# (CYCLEA & !Q1) # (!CLCLEA & Q1 &
Q2 & CLKA));
L1.OE = `B`1;
L2.OE = `B`1;
L3.OE = `B`1;
L4.OE = `B`1;
L4 = ((CHA3.sub.-- REQ & CYCLEA & !BRESET) #
(CHB3.sub.-- REQ & !CYCLEA & !BRESET));
L3 = ((CHA2.sub.-- REQ & CYCLEA & !BRESET) #
(CHB2.sub.-- REQ & !CYCLEA & !BRESET));
L2 = ((CHA1.sub.-- REQ & CYCLEA & !BRESET) #
(CHB1.sub.-- REQ & !CYCLEA & !BRESET));
L1 = (CHA.sub.-- REQ & CYCLEA & ! BRESET);
______________________________________
Referring to FIG. 5, the memory address decoding circuit consists of a
memory decoder 120, a type PLS153 logic device, which also controls the
BUSWIDTH line to microprocessor 80 to allow dynamic configuration of the
buss. The microprocessor 80 (FIG. 3A) executes program and data cycles on
a full 16-bit buss for speed. Peripherals occupy the lower byte of the
16-bit data word on an effective 8-bit buss.
The logic device 120 also controls WAIT state generation and can be
configured to insert 0, 1, 2 or 3 WAIT states during program, data or I/O
cycles. Two outputs from the logic device 120 determine how many WAIT
states are generated during a given memory access. Outputs SET 1 and SET 2
are gated to the PRESET and CLEAR inputs of the JK FLIP FLOPS 122 and 124
by means of inverter gates 126, 128, 130 and 132. A logic high on ALE from
the microprocessor 80 as applied to gates 126-132 via lead 134 enables the
gates. If SET 1 is low during ALE, the FLIP FLOP 122 will be cleared, and
if SET 2 is low during ALE, the FLIP FLOP 124 will be cleared. In effect,
the cascaded JK FLIP FLOPS form a 2-bit counter and their outputs are
decoded by the inverter gate array 126-132 to drive the READY input of
microprocessor 80 high whenever both outputs of the counter FLIP FLOPS
122, 124 are low. The counter is clocked by the trailing edge of the
processor 6 Mhz output which occurs when the sample window of the READY
input of microprocessor 80 closes.
The WAIT states are selected in the following manner:
0 WAIT--state SET 1 and SET 2 are low, both outputs of counter FLIP FLOPS
122 and 124 will be cleared and ALE and the READY line will be high. No
chip select is assigned during 0 WAIT states.
1 WAIT--state SET 1 and SET 2 are high, both outputs of the counter FLIP
FLOPS 122 and 124 are preset during ALE and the READY Line will be driven
low. CSRAM is assigned to 1 WAIT state.
2 WAIT states--SET 1 is low and SET 2 is high, output QA of the counter
FLIP FLOPS is preset high and output QB is cleared low during ALE and the
READY line will be driven low. The READY line will remain low until the
counter is clocked twice by 6 Mhz causing counter outputs to increment and
overflow to zero. CSROM is assigned to 2 WAIT states.
3 WAIT states--SET 1 is high and SET 2 is low, output QA of the counter is
preset high and output QB is cleared low during ALE and the READY line
will be driven low. The READY line will remain low until the counter is
clocked three times by 6 Mhz causing the counter outputs to increment and
overflow to zero. CSSIO and CSPIO are assigned to three WAIT states.
Output CSPIO from logic device 120 is applied into an integrated circuit
140, type 74C138N, which outputs a VCAMUX signal through an inverter gate
142. Another output on lead 144 through a gate inverter array 146 develops
an FXSWITCH output for employ in the audio processing channels.
Referring to FIG. 6, output VCACONT from microprocessor 80 is applied to a
voltage controlled amplifier 150 in the effects loops of the system.
Effects levels are controlled in the system by voltage controlled
amplifiers (VCA). Voltages are generated by the microprocessor 80
pulsewidth modulation output (PORT P2.5). This output is a 27K HZ square
wave of varying duty cycle. It is smoothed by the pulse width modulation
smoothing filter 150 which converts the square wave into a voltage from
zero to five volts DC that is linearly proportional to the duty cycle of
the pulsewidth modulator.
The pulsewidth modulator is time division multiplexed by the microprocessor
80 and a control voltage multiplexer 152, an IC circuit type 74HC435. The
multiplexer 152 thereby multiplexes eight different voltages onto the
effects control voltage sample holds. Thus, outputs X0 through X7 from
multiplexer 152 are applied to one of the eight different effects control
voltage sample holds comprised of type TL074N amplifiers 154, 156, 158,
60, 162, 164, 166 and 16S.
The voltage controlled amplifiers 154-168 control the various audio effects
as generated through the audio processing circuitry 26. The audio
processing and effects may be carried out in any of several known schemes.
Thus, audio may be directed through left and right channels through serial
EFX loops or parallel EFX loops and further processed through stereo
output channels in well-known manner. Thus, as shown in FIG. 6, the
voltage controlled amplifier 154 outputs effects 1 and 2 left, while
amplifier 156 outputs effects 1 and 2 right. The amplifier 158 controls
output of guitar left while amplifier 164 effects control of guitar right.
Amplifiers 160 and 162 output effects 3 left and 4 left, respectively, and
amplifiers 166 and 168 output effects 3 right and 4 right. Subsequent
mixing of individual component signals is carried out by effects switching
and amplification in well-known manner.
The foregoing discloses a MIDI guitar control system that can function to
convert guitar signals to MIDI information for controlling any
MIDI-equipped synthesizer. The control system is capable of controlling
the levels and stereo position of four external effects loops as well as
guitar amplification channel or reverberation selection. The pitch
detection system utilized in the present system is optimized to extract
the frequency of the fundamental of the guitar signal, i.e., the first
harmonic, and the second and other upper harmonics of the input signal are
attenuated by a programmable cut-off frequency filter.
The use of a programmable filter has two advantages. First, as perceptible
tracking delays exist at low guitar frequencies, optimization of tracking
delays is achieved by tuning the guitar to higher pitches and compensating
for this in the pitch detection software before sending the note to the
synthesizer. Previous systems have had the option of stringing the guitar
with all strings being the same gauge, e.g., all strings tuned to high E
(329.7 HZ-3ms). The present system allows the user to define his own
tunings, such as Nashville-type tuning, which tunes the lower three
strings an octave higher. This has the advantage that the guitar is tuned
correctly, and normal guitar sound can be used in conjunction with the
synthesizer sound. Second, with the tracking filters, an initial
measurement of pitch can be made with the input filter set at an initial
"guess" frequency. As more accurate pitch readings are made, the filters
adjust to track the pitch and thus optimize the tracking.
The present control system takes advantage of information that is present
in both positive and negative peak periods. The second harmonic is a
problem in period detection, and the use of a peak period FLIP FLOP "locks
out" the influence of the second harmonic on the period detection
operation. Whereas prior types of pitch detectors have used custom VLSI or
six hardware counters to implement pitch period counters, the present
system takes advantage of the four high speed inputs (HSI) of the
microprocessor as it is complemented by multiplexing logic to provide what
may be called a cost effective system of period measurement.
Changes may be made in combination and arrangement of elements as
heretofore set forth in the specification and shown in the drawings; it
being understood that changes may be made in the embodiments disclosed
without departing from the spirit and scope of the invention as defined in
the following claims.
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