US3827288A
Expired / Lapsed
US
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Digital servo control of random sound test excitation
Assignee: National Aeronautics and Space Administration
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Filing: 1972-03-16
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Granted: 1974-08-06
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Expires: 1992-03-16
Abstract
Abstract A digital servo control system for random noise excitation of a test object in a reverberant acoustic chamber employs a plurality of sensors spaced in the sound field to produce signals in separate channels which are decorrelated and averaged. The average signal is divided into a plurality of adjacent frequency bands cyclically sampled by a time division multiplex system, converted into digital form, and compared to a predetermined spectrum value stored in digital form. The result of the comparisons are used to control a time-shared up-down counter to develop gain control signals for the respective frequency bands in the spectrum of random sound energy picked up by the microphones.
Inventors
- 👤 J Fletcher
- 👤 R Nakich
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 19:59
CPC Classifications
G; G01; G01N; G01N29/00; G01N29/22
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
346 words
A method for controlling the generation of random sound energy in a reverberant acoustic chamber for the purpose of testing an object with a predetermined noise spectrum using a noise generator to produce a random noise electrical signal and a plurality of filters to separate said random noise signal into a plurality of narrow frequency band drive signals, a plurality of separate gain control means, a separate gain control means for each band drive signal, means for combining the outputs of said separate gain control means into a composite drive signal, and electropneumatic sound generating means for producing sound energy in said chamber in response to said composite drive signal, comprised of the steps of employing a plurality of sensors in said chamber to produce electrical signals, each sensor signal having frequency components of amplitudes which depend upon the location of the sensor in said chamber, obtaining a composite response signal from said sensor signals as an average of all said sensor signals, separating said composite response signal into a plurality of narrow frequency band signals corresponding to said narrow frequency bands into which said generated noise is separated, periodically comparing the energy level in each narrow frequency band signal of said composite response signal with a separately specified energy level of said predetermined noise spectrum to determine whether said response energy level of each channel is greater or less than said desired energy level for each channel, and incrementally adjusting the gain of said plurality of separate gain control means by one unit to drive the spectrum of noise being generated toward convergence with said desired spectrum, a given gain control means being adjusteD by one unit to increase gain if said response energy level of the narrow frequency band channel being controlled by said given gain control means is determined to be too low in the preceding step, and adjusted by one unit to decrease gain if said response energy level of the narrow frequency band channel being controlled by said given gain control is determined to be too high in the preceding step.
Claim 2
Independent Claim
346 words
A method for controlling the generation of random sound energy in a reverberant acoustic chamber for the purpose of testing an object with a predetermined noise spectrum using a noise generator to produce a random noise electrical signal and a plurality of filters to separate said random noise signal into a plurality of narrow frequency band drive signals, a plurality of separate gain control means, a separate gain control means for each band drive signal, means for combining the outputs of said separate gain control means into a composite drive signal, and electropneumatic sound generating means for producing sound energy in said chamber in response to said composite drive signal, comprised of the steps of employing a plurality of sensors in said chamber to produce electrical signals, each sensor signal having frequency components of amplitudes which depend upon the location of the sensor in said chamber, obtaining a composite response signal from said sensor signals as an average of all said sensor signals, separating said composite response signal into a plurality of narrow frequency band signals corresponding to said narrow frequency bands into which said generated noise is separated, periodically comparing the energy level in each narrow frequency band signal of said composite response signal with a separately specified energy level of said predetermined noise spectrum to determine whether said response energy level of each channel is greater or less than said desired energy level for each channel, and incrementally adjusting the gain of said plurality of separate gain control means by one unit to drive the spectrum of noise being generated toward convergence with said desired spectrum, a given gain control means being adjusteD by one unit to increase gain if said response energy level of the narrow frequency band channel being controlled by said given gain control means is determined to be too low in the preceding step, and adjusted by one unit to decrease gain if said response energy level of the narrow frequency band channel being controlled by said given gain control is determined to be too high in the preceding step.
Claim 3
Dependent Claim
79 words
A method as defined in claim 1 wherein said step of obtaining a composite response signal from said sensor signals as an average of all said sensor signals is comprised of the steps of decorrelating said sensor signals by delaying different ones of said sensor signals by different time periods such that no two are coherent, adding the delayed signals and dividing the sum signal by a number proportional to the number of sensor signals being decorrelated and averaged.
Claim 4
Dependent Claim
107 words
A method as defined in claim 1 wherein a given gain control means is comprised of means for multiplying a narrow band drive signal derived from said random noise signal by a second signal, and said second signal is controlled in amplitude to control gain in the last step, said last step being carried out by counting up an increment of one unit each time gain is to be increased, and counting down an increment of one unit each time gain is to be decreased, and converting the resulting value of gain control thus produced in digital form into analog form for use as said second signal.
Claim 5
Dependent Claim
117 words
A method as defined in claim 3 wherein said step of periodically comparing separately specified energy levels with the energy levels in respective narrow frequency band signals derived from said composite response signal is carried out by storing in digital form the values of said separately specified energy levels, averaging the amplitude of each narrow frequency band signal by converting it from ac to dc form, periodically sampling said narrow frequency band signals thus converted to a dc form, converting the amplitude of each sample into digital form, and comparing each sample in digital form with a specified energy level value in digital form stored for the narrow frequency band signal from which the sample was obtained.
Claim 6
Dependent Claim
68 words
A method as defined in claim 4 wherein said step of periodically comparing separately specified energy levels with the energy levels in respective narrow frequency band signals is so carried out that equality is interpreted to mean that a predetermined one of two values compared is greater, thereby causing the resulting gain control to continually seek a condition producing equivalence and not lock on a condition producing equivalence.
Claim 7
Dependent Claim
297 words
In apparatus for controlling the generation of random sound energy in a reverberant acoustic chamber for the purpose of testing an object with a predetermined noise spectrum, the combination of, means for generating a noise signal, filtering means for separating said noise signal into a plurality of narrow frequency band drive signals, summing means for adding signals to provide a composite signal, a plurality of voltage variable gain control means for coupling said drive signals to said summing means, an electropneumatic sound generating means responsive to said composite signal for producing sound energy in said chamber, said sound energy thus having a spectrum according to said noise signal as modified by said voltage variable gain control means, a plurality of sensor means in said chamber for producing electrical signals, each having frequency components of amplitudes which depend upon the location in said chamber of the sensing means producing it, means for producing a composite response signal from said sensor signals as an average of all said sensor signals, filtering means for separating said composite response signal into a plurality of narrow frequency band signals corresponding to said narrow frequency bands into which said generated noise is separated, means for storing desired values of energy lEvels of said predetermined noise spectrum, one value for each narrow frequency band into which said composite response signal is separated, means for periodically comparing said stored values of desired energy with energy levels of corresponding narrow frequency band signals, and means for producing a different gain control voltage for each gain control means, said gain control voltage means adjusting the voltage of a given voltage variable gain control means by one unit during each energy level comparison to drive the spectrum of noise being generated toward convergence with said predetermined noise spectrum.
Claim 8
Dependent Claim
297 words
In apparatus for controlling the generation of random sound energy in a reverberant acoustic chamber for the purpose of testing an object with a predetermined noise spectrum, the combination of, means for generating a noise signal, filtering means for separating said noise signal into a plurality of narrow frequency band drive signals, summing means for adding signals to provide a composite signal, a plurality of voltage variable gain control means for coupling said drive signals to said summing means, an electropneumatic sound generating means responsive to said composite signal for producing sound energy in said chamber, said sound energy thus having a spectrum according to said noise signal as modified by said voltage variable gain control means, a plurality of sensor means in said chamber for producing electrical signals, each having frequency components of amplitudes which depend upon the location in said chamber of the sensing means producing it, means for producing a composite response signal from said sensor signals as an average of all said sensor signals, filtering means for separating said composite response signal into a plurality of narrow frequency band signals corresponding to said narrow frequency bands into which said generated noise is separated, means for storing desired values of energy lEvels of said predetermined noise spectrum, one value for each narrow frequency band into which said composite response signal is separated, means for periodically comparing said stored values of desired energy with energy levels of corresponding narrow frequency band signals, and means for producing a different gain control voltage for each gain control means, said gain control voltage means adjusting the voltage of a given voltage variable gain control means by one unit during each energy level comparison to drive the spectrum of noise being generated toward convergence with said predetermined noise spectrum.
Claim 9
Dependent Claim
56 words
Apparatus as defined in claim 6 wherein said means for producing a composite response signal from said sensor signals as an average of all said sensor signals is comprised of means for delaying different ones of said sensor signals for different time periods, and means for adding said sensor signals after passing through said delay means.
Claim 10
Dependent Claim
80 words
Apparatus as defined in claim 6 wherein said means for producing a different gain control voltage for each gain control means is comprised of means for counting up an increment of one unit each time gain is to be increased, and counting down an increment of one unit each time gain is to be decreased, and means for converting the resulting value of gain control thus produced in digital form to analog form for use as said gain control voltage.
Claim 11
Dependent Claim
108 words
Apparatus as defined in claim 8 wherein said desired values of energy levels of said predetermined noise spectrum are stored in digital form and said comparing means includes means for converting each narrow frequency band signal to a dc signal proportional to the energy thereof, means for periodically sampling the energy of each of said narrow frequency band signals thus converted to dc form, means for converting the amplitude of each energy sample into digital form, and means for comparing each energy sample in digital form with a desired energy level stored in digital form for the narrow frequency band signal from which the energy sample was obtained.
Claim 12
Dependent Claim
68 words
Apparatus as defined in claim 9 wherein said means for comparing each sample in digital form with a desired energy level in digital form includes means for interpreting a condition of equality to be one of inequality with a predetermined one of two values being compared greater, thereby causing the resulting gain control to continually seek a condition producing equivalence and not lock on a condition producing equivalence.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-08-05 | 1978-02-04 | 1978-08-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-08-05 | 1982-02-04 | 1982-08-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-08-05 | 1986-02-04 | 1986-08-06 | $7700.00 | Window Closed / Lapsed |