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| United States Patent | 4457203 |
| Link to this page | http://www.wikipatents.com/4457203.html |
| Inventor(s) | Schoenberg; Steve A. (Clifton Park, NY);
Ellis; David G. (Ballston Lake, NY);
Aronstein; Jesse (Poughkeepsie, NY) |
| Abstract | A sound signal automatic detector used in a system with a micro computer
and display for automatically detecting an input sound wave, computing
from the detected sound wave the fundamental frequency of the sound and
displaying its value in a number of different formats. The sound signal
detector requires no attention on the part of a musician or other user
while it is in operation and comprises a sound signal transducer supplying
an amplifier having audio frequency bandpass characteristics compatible
with the sound signal frequency spectrum over which sound signals to be
analyzed extend. The bandpass characteristics of the amplifier preferably
are defined by a high pass filter stage followed by an automatic gain
control amplifier that in turn is followed by two stages of low pass
filtering. The low pass filter stages supply their output to an alternate
positive peak voltage and negative peak voltage detector circuit that
functions to derive an output signal which is representative of the
fundamental frequency of a input sound wave being analyzed. The output
from the automatic detection circuit is supplied to a micro computer which
then processes the signal and derives a number of different display
formats for use by an instrumentalist, vocalist, or other musician or like
person producing the sound for analysis and instruction purposes. |
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Title Information  |
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Drawing from US Patent 4457203 |
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Sound signal automatic detection and display method and system |
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| Publication Date |
July 3, 1984 |
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| Filing Date |
March 9, 1982 |
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Title Information |
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Description |
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TECHNICAL FIELD
This invention relates to a sound signal automatic detector method and
circuit and to the use of such detector together with a micro computer and
display in a system for automatically computing from a detecting sound
wave the fundamental frequency of the sound wave and displaying its value
in a number of different formats.
More particularly, the invention relates to a novel sound pitch detection
method and circuit and to the use of such method in an automatic system
further including a micro computer and display. The system is readily
operated in a hands-off manner by individual instrumentalists, vocalists
and other musicians or tuners of musical instruments in conjunction with a
widely varying number of musical instruments such as woodwinds, brasses,
pianos, harps, guitars, violins, percussion instruments and the like as
well as with the human voice for analysis and instruction or tuning
purposes. When placed in operation, the novel system listens to sound
waves emitted from any one of a number of widely different sound signal
sources such as those listed above and automatically detects the
fundamental frequency of a note. The results are then automatically
displayed in a format which can be preselected by the musician or other
user which will best assist the musician or other user in further
training, calibrating, tuning or otherwise improving the quality of the
sound being produced.
BACKGROUND ART AND PROBLEM
There are available to musicians, musical instructors and the like a number
of known different systems and methods for listening to and analyzing the
quality of sound waves being produced by musical instruments or the voice.
Some of these known prior art systems are typified by the disclosures in
U.S. Pat. No. 4,028,985, issued June 14, 1977 for a "Pitch Determination
and Display System;" U.S. Pat. No. 4,122,751, issued Oct. 31, 1978 for an
"Automatic Instrument Tuner;" U.S. Pat. No. 4,019,419, issued Apr. 26,
1977 for a "Tuning Device;" U.S. Pat. No. 3,896,697, issued July 29, 1975
for a "Device For Testing the Tune of Musical Instruments;" and U.S. Pat.
No. 3,722,353, issued Mar. 27, 1973 for an "Electronic Tuning Device for
Visual Tuning of Stringed Instruments." These are not all of the known
instruments and methods for analyzing sound signals as described briefly
above, but they do typify the type of equipment presently available for
sound analysis and teaching or tuning purposes. The difficulty with these
known equipments is that they are not easy to operate and simultaneously
calibrate while playing an instrument and provide read out displays that
are not easily interpreted by an operator, particularly a beginning music
pupil.
A primary goal of the present invention is to provide a musical instrument
sound signal automatic detection and display system which identifies
automatically a note being played without requiring assistance from the
instrumentalist playing the musical instrument. While the prior art
describes a number of automatic tuners which allegedly are capable of such
automatic operation, to the best of the inventors' knowledge such prior
art systems are commercially impractical and no devices are currently
being marketed which have an automatic identification feature comparable
to that made available by the present invention. The current, commercially
available, tuners all require that the musician or other operator specify
in advance the note he wishes to tune to, generally by setting a twelve
position switch to the desired note in advance of playing the note. Thus,
it is not possible to tune several different notes without requiring that
the operator remove his hands from the instrument he is playing to change
the note selector on the tuner. The system made available by this
invention does not require that the instrument operator specify the note
to be played in advance since a note being played will be determined
automatically by the novel detection and display system. This allows the
musician or other operator to play any note on his instrument or play
different notes, in any order, either in scales or at random to the best
of his ability without requiring that he break his concentration to
manipulate the sound signal automatic detection and display system.
The lack of foreknowledge of a note being played, is responsible for the
difficulty encountered in designing a suitable sound signal processor or
"front end sound detector" which can separate the fundamental frequency of
a note being played from the harmonics normally present in a musical tone.
In some instruments, such as the oboe, the harmonics are many times
stronger than the fundamental. Additional complications are introduced by
the presence of background noise and by the wide variation in the
amplitude of different sound signals to be analyzed.
The conventional approach utilized in currently available tuners is to
extract the fundamental frequency of a sound wave being analyzed by using
a narrow tuned filter or phase locked loop, which is set in advance by the
musician for a particular note to be played. Obviously, such known
techniques could not be used in the present system due to lack of advance
knowledge of which notes will be present in a sound wave being analyzed.
Accordingly, the invention makes available a novel front end sound signal
detector, which automatically works over a wide range of frequencies. An
alternate peak detector is the principal element employed in this novel
front end sound detector. It can extract the fundamental frequency of any
input sound signal without advance knowledge of the approximate frequency
value, since its operation does not depend on tuned circuits. Automatic
gain control and automatic filter stages enhance the performance
sufficiently to make the resultant output processed signal really useful.
The only way that the musician or other operator of the system has to
specify in advance information about a note to be played is with a
low/normal range switch which extends the useable range of the detector to
include some very low notes at the expense of some increased sensitivity
to background noise. Even with the selector switch in the "low" position,
the full range of notes in the musical scale can be processed by the
system.
DISCLOSURE OF INVENTION
It is therefore a primary object of the invention to provide a sound signal
automatic detection circuit and method for use with a micro computer
display in a system for automatically detecting an input sound wave and
thereafter automatically computing from a detected sound wave the
fundamental frequency of the sound wave and displaying its value in a
number of different formats useful to a musician, an instructor, a student
of music, a musical instrument manufacturer or an instrument tuner. The
system is reasily operated in a hands-off manner by a user of the
equipment after being initially placed in operation and provides an output
indication of the quality of sound being produced in a number of different
display formats. The formats displayed may be selectively used by an
operator of the equipment according to his needs.
Another object of the invention is to provide a novel alternate positive
polarity and negative polarity peak voltage detector circuit for detecting
and deriving an output indication of the value of the fundamental
frequency of an input signal wave being analyzed.
A further object of the invention is to provide a system having the above
characteristics which employs a novel automatic narrow bandpass filter
arrangement for improving the signal to noise ratio of the system.
In practicing the invention, a sound pitch automatic detection circuit is
provided which comprises a sound signal transducer for converting a sound
signal to be analyzed into an electrical signal having corresponding audio
frequency characteristics and a generally sinusoidal varying wave shape.
The audio frequency electric signal is supplied to an amplifier having
audio frequency bandpass characteristics compatible with the sound
frequency spectrum over which the sound signal to be analyzed extends. The
amplified audio frequency signal is supplied to alternate positive
polarity and negative polarity peak voltage detector for detecting the
first major positive going peak voltage and the first major negative going
peak voltage which exceed respective positive and negative threshold
voltage values and which occur in each fundamental period of the generally
sinusoidally varying waveshape electric signal. An output electric signal
representative of the fundamental frequency of the signal being analyzed
is derived from the alternate positive polarity and negative polarity peak
voltage detector. In preferred embodiments of the invention bandpass
filter means are connected in the circuit to pass only a desired portion
of the audio spectrum to be analyzed to the alternate positive polarity
and negative polarity peak voltage detector. The bandpass filter
preferably comprises a high pass filter stage having its output supplied
to an automatic gain control amplifier which in turn supplies two
successive, automatically adjustable low pass filter stages. The low pass
filter stages automatically adjust their frequency response
characteristics to lower the frequency passed by the two stages until such
point that the amplitude of the output signal from the output of the two
stages begins to drop below the amplitude value of the signal set by the
automatic gain control circuit at which point further restriction of the
frequency response of the two low pass filter stages, ceases.
The sound pitch automatic detection circuit is included in an overall
system further including a micro computer responsive to the output from
the alternate peak detector for measuring the elapsed time required to
derive an integral number of cycles of the fundamental frequency output
signal, and for dividing the integral number of cycles by the elapsed time
to thereby obtain a frequency signal that is indicative of the value of
the fundamental frequency of the sound signal being analyzed. The system
further includes a display which is responsive to the output from the
micro computer for displaying the value of the fundamental frequency of
the sound signal to an operator of the system.
In operation, the micro computer is programmed to sequentially compute
several measured values of the fundamental frequency of the sound signal
being analyzed and thereafter stores the computed fundamental frequency
measured value. The micro computer also includes a comparator for
comparing several computed measured values of the fundamental frequency
for correspondence to determine that the several values all lie within the
same range plus or minus a given tolerance and thereafter gates out the
computed measured fundamental frequency values to the display in response
to the several computed measured values lying within the same range within
the acceptable tolerances.
The micro computer further includes a musical note memory having the
frequency value of recognized musical notes comprising the musical scale
stored therein. A musical note comparator within the micro computer is
used to compare the computed measured value of the fundamental frequency
of a sound wave being analyzed to determine the frequency value of the
nearest recognized musical note and to derive an output error signal
representative of the difference in frequency between the sound signal
being analyzed and the nearest recognized note in the musical scale. The
display is responsive to this error signal so as to display to an operator
of the system the difference in frequency between the note that he is
playing and the nearest recognized note in the musical scale. The display
also identifies the nearest recognized musical note as determined from the
musical note memory.
The micro computer further includes a relative calibration factor
computation circuit and memory which is responsive to the measured
frequency memory and to the musical note memory for dividing the frequency
value of the nearest recognized musical note by the stored computed
measured value of the fundamental frequency of the sound signal being
analyzed and to derive the store in a memory a relative calibration factor
equal to their quotient. Selectively operated user controlled multiplier
means are included in the micro computer for selectively multiplying
subsequent computed measured fundamental frequency values of a sound
signal being analyzed by the relative calibration factor and the display
gate is actuated to display the output from the multiplier to the operator
of the system.
In addition to the above features, key select means are provided which are
selectively operable by an operator of the system and are connected to
control the micro computer for displaying to the operator the
identification of the note closest to that of the computed measured value
of the fundamental frequency of a sound signal being analyzed in the
appropriate notation or key which is most convenient for the operator.
Actuator means are provided which allow the operator to determine the
notation or key selected and also to change the notation or key by
advancing the key selected by one or more notes at a time.
BRIEF DESCRIPTION OF THE DRAWINGS
These and many other objects, features and attendant advantages of the
invention will be better understood from a reading of the following
detailed description when considered in connection with the accompanying
drawings wherein like parts in each of the several figures are identified
by the same reference numbers; and wherein:
FIG. 1 is a functional block diagram of one embodiment of an overall sound
signal automatic detection and display system according to the invention
and which comprises a front end sound signal detector, a microcomputer and
a display;
FIG. 2 is a functional block diagram of one form of an alternate peak
detector suitable for use as part of the sound signal detector in the
system of FIG. 1;
FIGS. 3A through 3D are a series of wave forms which illustrate the
operation of the alternate peak detector shown in FIG. 2;
FIG. 4 is a detailed circuit diagram of the input stage, the bandpass
filter amplifier stage, the alternate peak detector and output stages of
the automatic sound signal detection system shown in FIG. 1;
FIG. 5 is a more detailed functional block diagram of the essential
portions of the micro computer used in the system of FIG. 1;
FIG. 6 illustrates one format for a suitable display for use with the
system of FIG. 1;
FIG. 7 is a functional block diagram of a preferred form of automatic sound
signal detection and display system according to the invention and
constitutes the best known mode of practicing the invention at the time of
filing this application;
FIG. 8 is a detailed circuit diagram of the input preamplifier, high pass
filter and automatic gain control stages of the system shown in FIG. 7;
FIG. 9 is a detailed circuit diagram of one of the automatically adjustable
low pass filter stages employed in the system of FIG. 7 and FIG. 11
illustrates its operation; and
FIG. 10 is a detailed circuit diagram of a preferred form of alternate peak
detector utilizing a multiplexer employed in the system of FIG. 7 and
FIGS. 12 and 12A illustrates its operation.
BEST MODE OF CARRYING OUT THE INVENTION
FIG. 1 of the drawings is a functional block diagram of an overall sound
pitch automatic detection and display system constructed in accordance
with the invention. In FIG. 1, a microphone is shown at 11 for converting
sound waves to be analyzed into electrical signals that are supplied to
the input of a first stage audio amplifier 12. The microphone 11 may
comprise any conventional, commercially available microphone for picking
up sound waves and converting the sound waves into an electrical signal of
corresponding frequency to the frequency of the sound waves. The
microphone 11 and first stage audio amplifier 12 should be tailored to
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