US2403983A - Representation of complex waves - Google Patents

Description

July 16, 1946.

W. KOENIG, JR

REPRESENTATION OF COMPLEX WAVES Filed April 3, 1945 2 Sheets-Sheet l FIG. I

EDA?

MA6NETIG TAPE mzoumcr OSCILLATOR \8 VARIABLE AMPLIFIER RECTIFIER SCANNING FILTER FREO-UENCY ANALYZER MODULA srNcH/w/v/zma CONNECTION T INVENTOR W KOE/V/G, JR BY ATTORNEY July-16, 1946. KOENIG. JR 2,403,983

REPRESENTATION 0F COMPLEX WAVES Filed April 3, 1945 2 Sheets-Sheet 2 FREQUENCY FREQUENCY Ar rokzysy Patented July 16, 1946 UNETED LSTATEfi PAT-17E" a?! 'QEFIICE Bell Telephone Laboratories,

Incorporated,

'New York, N..Y.,.a corporation of New York Application April 3, 1945, Serial No.-586,308

Claims.

This invention relates'to the analysis of complex Waves and more particularly to the production of complexavave spectrograms.

It has been proposed heretofore to record complex waves, such as speechwaves'for typical example, in theform of a spectrogram or pattern the dimensions of which have the sense of coordinate axes representing frequency and time respectively, The character of the spectrogram is such that the effective intensity, or envelope amplitude, of the wave component or components appearing in'anyparticularfrequency band at any particular time is indicated in the pattern at the coordinate position respective to the particular frequency band and time. The amplitude m y be indicated, for example; by the density or blackness of thepattern at the respective coordinate position; as disclosed in mycopending application SerialNo. 568 88G, filed December 19, 1944.

One of the objects of the present invention is to produce complex-wave spectrograms of certain novel types disclosed herein. Another object is to provide simplified and improved equipment for producing spectrograms of types known heretofore. including spectrograms of the contour type disclosed in the copending' application'of R. K. Potter, Serial No; 569,557;filed December 23, 1944.

A'further-object is to'facilitate accurate determination 'of the' envelope amplitude indicated i-n-a complex-wave spectrogram,

Principal features of the invention lie in means provided for translating the variationsin envelope amplitude detected 'in any particular frequency band into variations in recording'current.

In accordance with embodiments of the'invention hereinafter to be described in detail, a beam 'of l-ight is deflected across a multiply-apertured screen or'mask' more or less in proportion to the -varying envelope amplitude of aselected component,-' and thelight intermittently transmitted through theapertures is utilized tocontrol the application of "marking "current to a recording stylus.

The nature of the invention 1' and its various features; objects and advantages will appear more fully on consideration of the embodiments illustratedin the accompanying 'drawingsand the fc-llowingdescription thereof.

the'drawings:

Fig. 1 illustrates an analyzing and recording system.in accordance with the present invention;

Figs." Zto Zillustrate rotatable screens that are .utilized; in modifications of the Fig. 1 system, in

theplace of'a .stationaryscreen and light modulating disc shownin'Eig. 1;

Figs. 8 to 12 illustrate various types of spectrogram produced in accordancewith the invention; and

Fig, 13 illustrates an optional auxiliary for certain of the modified systems.

Referring more particularlynowto'the system illustrated in Fig. 1, there is included ama'gnetic recordcnreproducer shown diagrammatically 'as comprisingan endless magnetic tape I which is passedpontinuously at asuitable'constant speed between the pole-pieces of an" electromagnet com. prising a coil 3. The 'complex'waves of 'which'a pattern is to be forme'd'may' bespeech bearing waves. for example, received from a microphone circuits which can be connected at will to coil 3 by 'means of a switchi. With the latter in its upper operating position the'incoming waves are recorded on the'magnetic tape I. Theswitch. is then opened and therecorded waves'are thereupon reproduced electrically or'played'back, repeatedly, once for each complete revolution, or cycle of movement, of tape 1.

With switch 5.121 its 'lowerposition'as shown, the WaVGSSOIEDIOdUCBd are passed to'a frequencyianalyzer or scanner of'the heterodyne type comprisinga modulator 1,W1'li01l is supplied with beating oscillations'from" an oscillator 8, and

bandepass or scanning filter '9 which is conn cted to receive the wave output from modulator "a. Modulator l efifectively translates the applied band of speech bearing waves to a'higherjposition in the frequency range depending on the frequency of the beating oscillations, and the latter frequency is varied continuously from one limiting value to another such that the translated band progressively shifts infrequencyposition, The total'shift of the'band is comparable with its width. Scanning filter il'has a relatively narrow pass band the mean frequency of which is such that as the translated'band wave shifts in frequency. filter 9 selects progressively different component frequency bands therefrom. .In eifect, the pass band of filter 9 moves gradually across the frequency range occupied by the speech bearing' waves and. admits the wave components appearing in the. different bands. The waves selected by filter 9 are passed to an amplifier-rectifier it, the constants of which are so chosen that the unidirectional output voltage is more-0r less proportional to the envelopeamplitude or efiective intensity of the selected waves. This voltage may be taken also as an approximate measure of the power content of the selected wave band.

The pattern recorder is illustrated diagrammatically in Fig. 1 as comprising an endless moving belt l2 of sensitized paper and a rotating threaded shaft IS on which rides a traveling nut I4 that carries the recording stylus [5 across the strip of paper. The latter may be dry facsimile paper, preferably one with a titanium oxide coating and carbon backing, such as the Teledeltos Grade H facsimile paper developed by the Western Union Telegraph Company. Belt I2 is driven at constant speed in synchronism with tape I by means of a motor or the like (not shown) connected to belt drum l6. Stylus I5, which may be a stainless steel wire mils in diameter for specific example, bears lightly against the recording surface of the facsimile paper and in the course of production of a spectrogram it is driven slowly across the paper, that is, longitudinally of the drum l6. Whenever and so long as electric current of sufficient intensity is supplied to stylus IS, the current passes through the stylus and the facsimile paper to drum it, which has a grounded conductive surface, and by virtue of the current passing through the point of contact of stylus l5 a mark is made on the paper.

The progressive change in the operating frequency of oscillator 8 is electrically or mechanically geared with the progressive change in the position of stylus so that as the stylus moves once across the facsimile paper, the oscillator frequency progresses from its one limiting value to the other. This operation is completed only after many revolutions of the belt l2 or in other words only after many reproductions of the recorded waves. In one instance in practice, for example, in which a 3500-cycle band of speech waves was to be recorded the parts were so arranged that the complex waves were reproduced 200 times while stylus I5 moved once across the facsimile paper. Disregarding the slight change in the frequency of oscillator 8 that takes place during each reproduction of the speech waves and the corresponding slight change in the frequency band selected by filter 9, it will be understood that during each reproduction of the recorded waves the filter 9 selects a definite predetermined frequency band while the stylus l5 traverses a respectively corresponding path substantially longitudinally of the facsimile paper, 1. e., lengthwise of the belt. The mechanism for supplying current to stylus I5, which will be described presently, is such that along each path on the paper the stylus leaves a trace that is interrupted in a variable manner depending on the varying envelope amplitude of the respectively corresponding band of waves selected by filter 9.

The Fig. 1 system includes also a mirror galvanometer comprising a mirror 2| and a driving coil 22 both mounted for limited rotary movement about a vertical axis. Coil 22 is connected to the output terminals of amplifier-rectifier l0, and the mirror 2| is therefore deflected from its rest position more or less in proportion to the envelope amplitude of the wave components that are selected by filter 9 at any time. Light from the vertical filament of an incandescent lamp 23 is directed through an optical system symbolized by lens 24 to mirror 2| from which the light is reflected in a beam 26 that varies in horizontal direction according to the varying deflection of mirror 2|. Disposed horizontally across the path traversed by beam 26 is a semicylindrical lens 2'! which extends radially along the face of a rotary screen 28. Interposed between lens 21 and screen 28 is a stationary screen 29 in the form of an elongated mask that has a multiplicity of t fansverse slits 30 spaced apart at different distances from the axis of rotation of screen 28. The latter is disposed in the focal line of lens 2"! and it serves to chop or interrupt intermittently any light that passe through the openings 30 to an elongated photoelectric cell 3i. Screen 28 may comprise a multiplicity of transparent and opaque sectoral portions disposed in alternation, in which case it is disposed between screen 23 and photoelectric cell 3i as shown, although alternatively it may comprise alternate light reflecting and light absorbing portions, the photoelectric cell 3| in such case being so disposed as to receive the interrupted reflected light. In either case the varying light emanating from the screen 28 and reaching the photoelectric cell 3i gives rise to electric currents of corresponding varying intensity in the photoelectric cell circuit 32. The currents are intensified by an amplifier 33 and then transmitted to the stylus l5.

In the operation of the Fig. 1 system the beam 26 sweeps back and forth along the screen 29, following the variations in envelope amplitude of the wave components selected by the frequency analyzer, The several slits 30 are respective to different discrete values of envelope amplitude. for beam 26 is incident on a given slit only when and so long as the envelope amplitude has a predetermined particular value. The light momentarily passing through a .particular slit 3!} tends to produce in circuit 32 a unidirectional current pulse of corresponding duration. The screen 28. however, is rotated at a speed such that the light reaching photoelectric cell 3| is interrupted repeatedly at a high rate such as 10,000 times per second for example. The result is that the current supplied to stylus I5 is alternating in character, which is substantially more effective in marking the facsimile paper than a unidirectional current. While the frequency analyzer selects the waves in a particular component frequency band, therefore, the stylus l5 traverses the corresponding longitudinal ath on facsimile paper [2 and produces a mark whenever the envelope amplitude of the selected wave passes through one of the predetermined values.

Fig. 8 illustrates the type of spectrogram that is produced by the Fig. 1 system, assuming that the width of the slits 30 is small in comparison with the distance between them. The marks made in the course of successive reproductions align themselves, it will be observed, to form contour lines such as 31, 38, 39, in Fig. 8. Each contour line is identified with a particular value of envelope amplitude. The envelope amplitude pertaining to any particular frequency band and time may be determined by noting what contour line, if any, passes through the corresponding coordinate point On the spectrogram, or by interpolating with reference to the adjacent contour lines. One will observe i Fig. 8 several regions where the beam 26 repeatedly dwelt on a particular slit 30 long enough to produce horizontal lines of appreciable length. In such regions the contour line takes on the appearance of a band.

Th width, number and spacing of the slits 30 can be adjusted to provide a variet of difierent effects. If the width of the slits 30 is made equal to the spacing between them, for specific example, all of the contour lines will appear as bands or, in other words, successive contour zones in the spectrogram will appear alternately light and shaded, respectively. If the Spacing between slits is small compared with the width of the slits the resulting spectrogram comprises light contour lines 011 a In taccordancawith a further. modification of= 'theIZE'ig. l:system, the :screens 28 -and .z2.9iare -zre .placedjoy asingle.'rotaryscreen-cf the kind illustratedsin'fFig. 2. The shaded' areas inJiig. 2 rep- :resent;transparentportions of thescreen. .These iportions define; in part, .a multiplicity of marrow concentric:light-chopping bands-4 I. The several bands-Al are identified with:respectively correspondin different values of -envelcpeamplitude and beam deflection, land their presence results 1111 the formation, of corresponding .contour lines inthe spectrogram substantially as illustratedv in .Fig. 8. The intervening annular zones. 42, :which are identified with respectively -corresponding different ranges" of enve1ope amplitude-values and of (beam "deflection, are opaque-iexceptfor occasional sets of closely spaced, .ra-di-al transparent portions-43. The severallsets of transparent portions-43 are uniformly spaced aroundeach zone -4 2,.-but their angular-separation (1801'885851131'0- ."gressive ly from aemaximum in theinnermost'or low-amplitude zone. Whenever and so long 3.313136 .light beamzfi impingesrononecf the zones 42, it gives; rise in circuit 32-toa succession of .current pulses, each. of anfalternating character adapted for efiective marking: of the facsimile paper, .and.

the timecinterval betweenpulses depends on the :radius Ofthepart-icular rzone. :Theumarks .pro-

duced by the stylus ii in any giveniong-itudinal path are-spaced.inproportion to-thetime separation eftthe currentpulses, and;they.-are substantiallyuniform. in size. Thus reachrange .of .en-

velope amplitude is identified with :a .particular .zone- 42,. with .a particular manner of. modulation of the .marking circuit, via, a particular-spacing.

the marksappearingin the maximum amplitude 2 .regions of .the spectrogram are =longitudinally continuous.

The-rotary screen illustrate-d in Fig. 3 z-issub- .stantiallyithe. sameas that shown in .Fig. 2,. ex-

cepting for :omission of the light chopping-rings 4 I and inequality of thew-idth of the several. zones 42. The latter are graded logarithmically from .minimumwidth in the innermost zone-.to maximum width in the outermost: zone. There being five ofthe. zones 42, thespectrogram-exhibits "five i6 distinctly .difierent :interedot spacings, and five .dififerent logarithmically related ranges :of envelope amplitude ear gindicated in :thespectrogram. The general appearance of the: spectro- 5 ggram is illustrated in Fig. 9, which pictures "a fragment 10f a speech spectrogram. The Joand width of the scanning filter 9 employed inz-obstaining 1 this. spectrogram Was approximately ,300 cycles, or .wide enough to suppress detail of the harmonic structure. The marks may be. caused to so align -.themselves as.toformrshading lines of variousslopes. Thus, .by: maintaining ,thepperiod- .of rotation of the .screen in:- accurate .har- .monic-.relat-ion to the period of movement'of .belt -.l.2,. all.ofthese shadinglinesmay he made vertical. .By maintaining afixedinharmonic relationfhowever, .theshading' line maybe made to slopedif- .ferently for each.different.oontour zonetin the spectrogram. This is illustrated diagrammatically, in. Fig. 1.0. Theamplitude range pertaining .toiany given. zone-it is evident, can be identified by the inclination of th shading lines, andbythe spacing of the shading lines. Therate.of.rota- -tion of the screen may beallowed to vary-slightly if it .be. desired to: prevent the formationrof. such shading-lines.

Figs. 4 .and -5 -.illustrate rotary screens 'of .a typesuchthat thelength of the markmadeby .stylus .l.5 issensibly dependent .on theiamou-nt of deflection of beam .26 .and thereforealso on .the .envelope amplitude. Eachofthese screens may .be regardedas -.beingrdivided into an integral numberzof eq-ual sectors in. each of which .the light-chopping striationstll l extend from. the .leading edge of :thesectorwarcuatelyi towardthe .trailingedge to an :extent that increases aprogress-ively .with progressive increase -.-in distance from theaxisofrotation. In Fig. .4: theprogres- .sive .increase in -.arcuate extent is substantially cntinu'ous whereasin Fig. it.take .place in several distinct steps. .Wherever .the beam -.-of -light 26 strikes it .will ,be transmitted through the. screen, modulated. atthechopping.frequency, -at regularly-recurring times,.heginning each time 45 -as -the -leading.ecige of .a :sectorpasses through .,the beam .and continuing for a period that .de- :pends .on the position .of. the .beam. .TI'hermarks producedbystylus l5 are made-likewisev atregularly recurring. intervalsand their lengths .are -50.correspon'dingly variable, cbeing .least for low values of envelope amplitude andprogressively greater for higher values thereof. The. character and appearance of the spectrogram depends on "how fa'stithe .screenlis rotated and onlthe .con- ;55 stancy offits speedin. relationto that of-belt. l2.

-If an exact -harmonic espeed relation .is ,main- .tained one obtains a spectrogram .of .the kind represented in Fig. 11, in which the-markspertaining to successive time intervals-are aligned in corresponding successive frames. If the speed relationis allowed to vary, the alignment of the le'ftehan'd extremities of the. marks shown in'Fig. 11 will.not bev maintained. 'Thelength ofeach line, however, will remaincameasure of.the en- .velope amplitude pertaining to the particular Q frequency band. .andtime indicated .by .itscoordi- .nate, position. .Dependingon the relation of .the various factors noted above..Fig. .lLmayhe taken as an .unmagnified representation .of. the spectrog'm ,gram .or as .a greatly magnified representation.

.In the .latter case.- the spectrogram, .held at.- normal viewing distance, wouldiappearas a half tone picture.

Thev rotary screenillustrated inEi 6. is vclosely r'lfirelated to thatdescribed .withreference .to Fig.

4. The light-chopping striations extend radially inward from the periphery and vary in length continuously at logarithmic rate in both circumferential directions from a minimum length at the left to a maximum length at the diametrically opposite point. The central opaque section of the screen is roughly heart-shaped. The spectrogram obtained by using the Fig. 6 screen is similar to that illustrated in Fig. 11 except that the horizontal lines in each frame along the time axis are symmetrical about a vertical axis.

Each horizontal line in a spectrogram of the type described with reference to Fig. 11, it will be understood, is produced by a continuous series of light-chopping striations of corresponding arcuate extent. By breakin the continuous series into several spaced sets of striations, each horizontal line in the spectrogram can be made to appear as a dotted line, the number of dots to be counted in any line being a measure of the envelope amplitude. Fig. 12 illustrates such a spectrogram and Fig. 7 shows an appropriate type of screen.

In certain analytical work it may be desired to have in addition to the spectrogram a record of the average power or envelope amplitude, or of the total energy, associated with each of the bands selected by the analyzer. If the spectrograph is so designed that the power contentor envelope amplitude i represented by a proportional number of dots the desired record can be had by recording the total number of marking current pulses that appear during each reproduction of the recorded waves. For this purpose the current pulses may be applied to a counting the beginning of the next the accumulated charge is caused to operate the amplitude recording apparatus. Such an auxiliary to the spectrograph is illustrated diagrammatically in 'Fig. 13, which shows a pulse accumulator 45 connected to photoelectric cell circuit 32, and a switch 46 which may be operated manually or automatically at the proper time to apply the accumulated charge to deflecting coil 24. A mark is thereby made at the end of each line in the spectrogram, and the character of the mark varies according to the total number of dots in the line.

It will be understood that the embodiments herein disclosed are in some respects only illustrative of preferred forms and that the invention i susceptible of embodiment in various other forms within the spirit and scope of the appended claims.

What is claimed is:

surface a visual representation of complex waves in the form of a pattern the dimensions of which have the sense of a frequency axis and a time axis, respectively, frequency analyzer means opill I ordinate position respective to each.

1. In a system for producing on a record light to said aperture means selectively according 2. A system of the kind described comprising means for repeatedly reproducing a complex wave, frequency analyzer means for selecting during each successive reproduction the wave components appearing in a respective different component frequency band, a rotating screen, means for directing a beam of light to said screen, means for displacing said beam relative to and across said screen under the control of the selected components to different positions respective to each different effective intensity of the selected components, a photoelectric device exposed to the light incident on and emanating from said screen, means for modulating the light emanating from any of a multiplicity of annular regions concentric with the rotational axis of said screen comprising screen portions of dissimilar optical character disposed in alternation around each said annular region, the several said annular regions and the said portions thereof being of such size and spacing that the modulation of said light is distinctively different for ifferent displacements of said beam, and stylus means for marking on a record surface along successively different collateral paths during respective different reproductions of the said complex waves, said stylus means being responsive to electrical currents produced by the exposure of said photoelectric device to said modulated light.

3. A system in accordance with claim 2 including means, comprising said screen, for modulating said light in substantially the same manner throughout each of different ranges of displacement of said beam, the manner of modulation differing distinctly from any one of said ranges to another.

4. A system' in accordance with claim 2 including modulating means, comprising said screen, for impressing on the said emanating light a series of spaced pulsations, the duration and spacing of the pulsations being different for different ranges of displacement of said beam.

5. A system of the kind described comprising means for repeatedly reproducing a complex wave, frequency analyzer means for selecting during each successive reproduction the wave components appearing in a respective different component frequency band, a rotating screen, means for directing a beam of light to said screen, means for displacing said beam relative to and across said screen under the control of the selected components to different positions respective to each different effective intensity of the selected components, a photoelectric device exposed to the light incident on and emanating from said screen, means comprising said screen for varying the intensity of the emanating light in pulses of alternating character the time separation of which changes progressively with progressive change in the extent of displacement of said beam, and stylus means for marking on a record surface along successively different collateral paths during respective different reproductions of the said complex wave, said stylus means being responsive to electrical current produced by the exposure of said photoelectric device to said modulated light.

6. A system in accordance with claim 5 in which the said time separation progresses substantially in discrete steps.

7. A system in accordance with claim 5 in which the said time separation progresses substantially continuously.

8. A system of the kind described comprising means for storing complex waves, means for repeatedly reproducing the stored waves, frequency selective means for derivin from the reproduced waves an effect that varies during each successive reproduction in accordance with the variation in eifective intensity of the wave content of a different component frequency band, current-responsive stylus marking means movable relative to and across a sensitized surface along a multiplicity of collateral paths in succession, each of said paths being respective to a difierent component frequency band and each being followed by said marking means while the said effect is being derived from the said respective frequency band, means for producing a beam of light that is displaced variably in conformity with the variations in said derived effect, photoelectric means positioned to receive the said beam, a screen interposed in the path of said beam, said screen having apertures spaced apart to pass said beam selectively in dependence on the extent of displacement thereof, and means for applying the currents produced by said photoelectric means to control the response of said current-responsive marking means.

9. A system in accordance with claim 8 in which said screen is stationary.

10. A system in accordance with claim 8 in which said screen comprises a rotatable element having a multiplicity of spaced apertures in each of a multiplicity of rings concentric with the axis of rotation, said system including means for rotating said element at a speed such that the light incident on each ring is modulated at audio frequency.

WALTER KOENIG, JR.

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