US2239042A - Wave recording and reproduction - Google Patents

Description

April 22, 1941. J. o. KLEBER FETAL WAVE RECORDING AND REPRODUCTION 2 Sheets-Sheet 1 Filed June 12, 1939 X V T dized range+ FREQUENCY n J SEW H ROD v V I 0 S 1 n T EL D! R X M M w VKO T m 1 F 0m N m N u o finwfi M m MM D I F a JM 1 2 R VUT CC u n ll I k F F f Xw m m 0 0 B.N\ .BW 3 F F April 1941. J. o. KLEBER ETAL 2,239,042

WAVE RECORDING AND REPRODUCTION Filed June 12, 1939 2 Sheets-Sheet 2 tmJ p 1g 1 -Q w F a Fig/0. 54 4 5 'L d) A 50 A v v.

INVENTORS I I A TTORNE y Patented Apr. 22, 1941 UNITED STATES Parent orricr.

WAVE RECORDING AND REPRODUCTION Jackson 0. Kleber, Long Island City, N. Y.,' and Lincoln Thompson, Stamford, Conn, assignors to The Sound Scriber Corporation, Stamford, Conn, a corporation of Connecticut Application June, 12, 1939, Serial No. 278,572

1'2 Claims.

This invention relates to wave transmission methods and means, particularly as applied to the recording and reproduction of sound waves or other waves in low speed record tracks.

In order to compress as much record as possible into a given length of record track, when making a record of sound or other waves, it is desirable to make the recording stylus or other recording device trace the track at a relatively low speed. For example, when a sound record disk rotates at the commercial speed of 33 revolutions per minute, more than twice as much record can be included in a given length of groove as at the commercial speed of 78 revolutions per minute.

Difliculties arise, however, when the linear speed of the record track is low. In the case of a disk record, thetrack speed is proportional to the radius of curvature of the track, and the speed of the track is so much lower at its inner end than at its outer end that the record is excessively compressed and sufiers serious attenuation or loss of the higher frequency components in the reproduced waves at the disk speed of 33 revolutions per minute. The wave lengths of the components of a complex wave recorded in the track, become progressively shorter as the ire quencies of the components increase, until at the higher frequencies and the lower track speeds, the reproducing stylus appears to be unable to follow faithfully the fine structure of the recorded waves representing the components of higher frequency, and the reproduced waves are correspondingly distorted or incomplete. 7

Further difficulties are encounteredif an attempt be made to increase the amplification of the recording current to avoid loss of the higher frequency components. The lower frequency components in this case are recorded and reproduced in such excessively large amplitudes, while the higher frequency components are, in general,

reproduced in such small amplitudes at the low track speeds, that the higher frequency components are seriously masked or completely obliterated by the more powerful lower frequency components. I

Owing to the relatively short wave lengths of the higher frequency components in the record track at low track speeds, the peaks of these components tend to block the passage of the reproducing stylus along the groove and; tend to squeeze the stylus out of the groove as the amplitudes of the higher frequency components increase. In this way the reproducing stylus may be forced to jump completely out of the groove.

In some cases the jump may be so violent that the stylus does not return to the same turn of the groove. Squeezing of the reproducing stylus tends to distort, interrupt and otherwise mutilate the reproduction of the desired waves.

Similar difiiculties may be experienced at various low speeds of rotation of the disk type of record, and also with other types of records operating at relatively low track speeds.

An object of the present invention is to provide simple and convenient methods of and means for transmitting waves so that the waves are adapted for recording and reproduction in more intelligible and useful form and so that one or more of the above mentioned difficulties may be reduced or avoided.

Another object is to compactly reccrdwaves, for example sound waves, in such a manner that the waves reproducible from the resulting record exhibit less objectionable distortion, loss of identity, or mutilation when compared with the original waves, than would occur when employing the usual methods of recording at corresponding track speeds.

Another object is to apply the methods and means, referred to above, to records of the disk type.

Another object is to provide a recording circuit and a reproducing circuit adapted selectively to transmit waves without incurring shock excitation dimculties.

Other objects are to provide simple and eliicient methods of and means for varying the recording characteristics of a wave recording system automatically with change of track speed; to provide a simple and efiicient amplifying system in which the characteristics of the amplifier may be varied readily, either at the amplifier or at a place remote from the amplifier; and generally to im- 7 the direction of the groove at the prove the transmission and other characteristics of wave recording and reproducing systems utilizing relatively low track speeds or utilizing wave lengths in the'record track which are short as compared with the dimension of the reproducing stylus or other reproducing pick up measured in place being traced.

In accordance with one aspect of the present invention, sound waves or other waves to be recorded, are given a preliminary compensation or distortion in a predetermined manner during transmission through a section of the wave path between the source of waves and the recorder, so that certain of the waves or components of different frequency are transmitted to the recorder with relative amplitudes differing from their original relation and so that the waves are recorded in a form adapted for reproduction as a more faithful, more intelligible, or otherwise more useful copy of the original waves.

When the invention is employed for recording on disk records, the waves may be compensated or distorted in portions of the track of smaller radii or of lower track speed, by recording the higher frequency components with a greater amplitude in proportion to that of the lower frequency components than occurs in the waves from the original source, while the waves are recorded in portions of the track of larger radii or higher track speed, either with less compensation or without any compensation. The band of higher frequency components being recorded at the greater amplitude, is preferably increased in width with decrease of track speed, or conversely, the band width is decreased with increase of track speed by changing the transmission characteristic of the wave path. In order to control the relative amplitudes of components of the waves being recorded and the width of the band having increased amplitude, one or more cams may be provided to vary the transmission characteristic of the path in predetermined relation to the recording mechanism, to automatically and progressively change the amount of compensation in the recorded wave with change of track speed, thus varying the transmission of the'recording current with frequency according to a predetermined family of curves. By substituting for one cam, another of different contour, a change may be made from oneto another predetermined set of curves, so that various different characteristics may be obtained in the reproduced waves without requiring replacement of the impedance elements. A similar cam arrangement may be employed for varying the relative amplitudes of components of the waves reproduced from a record with changes of track speed.

The band of higher frequency wave components recorded with increased amplitude, is preferably limited to a predetermined upper level or maximum gain, thus minimizing objectionable squeeze of the reproducing stylus. When the track speed becomes so low that the compensated higher frequency components of larger amplitude tend to produce a record which might objectionably squeeze the reproducing stylus, as referred to above, the cam is preferably provided with such a contour as to reduce the amplitude of the higher frequency components at the low track speed to minimize objectionable squeeze, while maintaining the amplitude large enough to insure more intelligible reproduction than in the case where the different frequency components are recorded with the same amplitude relation as in the original'waves.

In a convenient form of the invention, an amplifier is provided with a negative feed back, having a selective circuit so combined therewith that the resulting, amplification, in terms of the ratio of output to input of the amplifier, may be made greater for the components of one frequency than for those of another frequency. The negative feed back circuit includes a coupling circuit between the output and input circuits. A selective circuit is so associated with this feed back circuit as to selectively reduce the negative feed back efiect for components of a certain frequency or frequencies, thus causing an increased amplification thereof. The selective circuit thus serves as a selective neutralizer for the negative feed back coupling for selectively uncoupling the feed back and thus 7 but may be of any other suitable type.

.cator 35 is connected in parallel with the recorddistorting the waves transmitted through the feed back and the amplifier. By employing reactance of only one sign in the selective circuit, shock excitation difliculties may be avoided. The need of a volume control for the uncompensated components is also avoided, and more flexible, eiiicient and convenient control and operation of the amplifier is possible than when ordinary selective networks outside of the amplifier are employed to control the selective transmission of the current.

These and other objects and features of the invention will be understood more clearly from the following detailed description in connection with the accompanying drawings and the appended claims.

In the drawings,

Fig. 1 is a schematic diagram of one form of circuit illustrative of the invention.

Fig. 2 shows curves representing decibels of gain for current reproduced at different track speeds from a record without high frequency compensation.

Figs. 3 and 4 show curves representing decibels of gain for compensated recording current with difierent adjustments of the compensation circuit of Fig. l or '7.

Fig. 5 shows a different form of compensating circuit for substitution in Fig. l or 7.

Fig 6 shows curves obtainable with the Fig. 5 circuit.

Fig. 'l is a schematic diagram of a push-pull amplifier circuit adapted for substitution in Fig. l.

Fig. 8 is a schematic diagram of a reproducing circuit.

Fig. 9 shows a curve representing decibels of gain in the compensated amplifier of Fig. 8.

Fig. 10 is a schematic diagram of a wave transmission circuit adapted for substitution in Fig. 1, and having a selective shunt across the line to compensate the recording current.

Referring to Fig. 1, the microphone or other source of waves I to be recorded, is coupled with the pre-amplifier 2, labelled A1, coupled in turn with the transmission control amplifier 3, A2, coupled with the power amplifier 4, A3, coupled with the recording head 5, RH, having the recording stylus 6. The recording head 5 is shown as being of the usual inductive impedance type,

An indiing head 5 to show the amplitude of the waves being recorded.

The constant speed motor 7, M, rotates the feed screw 8 to feed the recording head toward the center of the record disk blank, [0, or in a reverse direction by reversing the rotation of the feed screw 8. The disk I 0 is supported on the usual turn table I I, having the constant speed drive shaft 9 for rotating the disk in a clockwise direction.

The amplifier 3 has the input transformer coupling or impedance l2 and the output transformer coupling or impedance l3. The input circuit M of the amplifier, connected from the cathode P5 to the control element or grid [6, includes in series in the order named, the resistance ll, the negative feed back coupling resistance 18, and the secondary coil of the input transformer The output circuit l9, connected from the cathode l5 to the anode 20, includes in series in the order named, the resistance ll, the source of current 2| for positively polarizing anode 28, and the primary coil of the output transformer l3.

The desired amount of negative polarizing potential for grid I 6 to insure of linear amplification, is obtained by adjusting resistance l1. The capacity 22 shunting the resistance l1, bypasses alternating current components around the resistance.

The variable resistance 23 in series with the low impedance blocking condenser 24, is connected from the output circuit I9 at the anode 26, to the input circuit I4 at the terminal of resistance l8 remote from resistance 11. The se-v lective compensating circuit 25, shunted aroundcoupling resistance I 8, includes impedance ele ments consisting of the variable capacity condenser 26 in series with the variable resistance 21.

One end of the rack bar28 is attached to the recording head 5, the other'end' being slidable longitudinally through the fixed guide 29, while the head 5 is fed across the disk Ill. Rack teeth 30 along one edge of bar 28, mesh with one or more pinions 31, 3|, etc., fast to one or more shafts 32, 32, etc., free to rotate in and supported by the stationary frame 33. One or more cams 34, 34, etc., removably-supported on shafts 32, 32, etc., respectively, may be locked thereto by hand screws 36, 36, etc. One or more cam-following plungers 31, 31, etc., are free to slide longitudinally while guided by the frame 33, the plungers being pressed endwise into contact with the cams 34 by the springs 38, 38, etc., compressed at one end by the frame 33 and at the other end by the collars 39, 39, etc., fastened to the plungers 31. Rack teeth 40 along the edge of each plunger, mesh with a pinion 41, fast to each shaft 42, jour:

naled in frame 33. Rotation of one shaft 42, varies a the capacity of condenser 26, and rotation of an-' other shaft 42, varies resistance 21.

When the recording head 5 feeds toward the center of disk ID, the rack bar 28 causes the rota tion of pinions 3| and earns 34 in a clockwise direction, thereby controlling the longitudinal position of plungers 31, which in turn control the rotational positions of pinions 4| and shafts 42, and the corresponding adjustments of condenser 26 and resistance 21, so that the compensation circuit 25 automatically may be given a desired predetermined adjustment by cams 34, at each part of the record track to correspond with the linear speed of the track, the adjustment of circuit 25,

being synchronized with the movement of the recording head 5. Condenser 26, resistance 21, or any other unit, when there are added units as referred to hereinafter, may be varied, or may be held at a fixed value by a cam 34 having a circular contour of suitable diameter.

The usual recording conditions of ordinary recorders may be simulated, if the amplifiers A1, A2, A3, operate as ordinary amplifiers without special provision for frequency selectivity, This result may be obtained with the Fig. l circuit, if resistance I8 be first adjustedto a very low or zero.

value, while resistance 23 is made so high as to act as an open circuit, the amplifier A2 performing as an ordinary amplifier without feed back, and the cam control mechanism consequently be ing ineffective to produce any control over the recording current. Assuming sound or other waves within the usual recording frequency range,

originating at constant amplitude at the source- I, are transmitted to amplifiers A1, A2, A3, and the recording head 5, the resulting record track when played back in a reproducing operation, reproduces waves with a gain shown by thecurves T, V, X, Fig. 2, corresponding, respectively, with the maximum track radius or speed. range T, the in? termediate range V, and the minimum range X, Fig. 1.

. While the ideal reproduction characteristic for most purposes might be a horizontal line through-- out the utilized frequency range, it will be seen that the actual reproduced waves suffer from serious attenuation or complete loss of the higher frequency components at the low track speeds. The loss of waves shown by the curve X, Fig. 2,. is so serious in the case of a speech record, for example, that there may be an almost complete loss of intelligibility, thus making it necessary when intelligibility is desired, to uneconomically limit the recording area, when recording by the old method, to an area of the disk having a relatively large radius.

In order to improve the reproduction of higher frequency waves in accordance with the presentinvention, the resistance 23 is first adjusted to permit appreciable current to pass from the output circuit IE! to the input circuit l4, the coupling resistance l8 being made large enough in relation to resistance 23 to provide an efiicient negative feed back action, whileresistance 21 is first made so highthat compensation circuit 25 exerts no appreciable effect on the feed back. The compensation circuit 25 may then be adjusted to any desired value to selectively shunt the resistance coupling I8 and thereby to give the amplifier 3 a frequency selective characteristic or in other Words a predetermined distortion characteristic having the desired compensating effect. It will be seen that circuit 25, by virtue of its shunting action, is adapted to selectively neutralize or uncouple the negative feed back coupling I8, thereby causing a selective increase in amplification;

The impedance characteristic of the condenser 26 in series with the resistance 21, as an uncoupling circuit, has been found to be especially eifective and convenient for a wide range of adjustments of the transmission level of the components of different frequency to be recorded. One advantage is that the use of a selective circuit having only one kind of reactance therein,

' makes it possible to avoid shock excitation effects,

thus improving the quality and intelligib ility of the reproduced waves. Another important advantage is that the impedance of circuit 25 at any given setting can be made to decrease smoothly as the frequency increases, so that the resulting amplification increases smoothly for the'higher frequencies to be recorded. A further advantage is that the low frequency components which need no increased amplification for the low track speeds, remain unaffected by the compensation circuit 25. The need for an extra volume control for the amplifier is thus avoided. A still further advantage with this form of circuit, is that the point on the frequency scale where waves of increasing frequency begin to receive an increase of amplification, may be readily adjusted up or down scale by merely adjustingthe value of condenser 26 or resistance 21. The slope of the curve of increasing amplification may be conveniently adjusted within wide limits by adjusting resistance 21. Since no inductance is needed in this form of compensation circuit, the problem of stray magnetic fields and magnetic shielding is avoided. The type of amplifier shown in Fig. 1 is particularly adapted to have its compensation control circuit 25 placed at a distance from the other parts of the amplifier circuit for convenient remote control.

Cams 34, 34, are given such contours that they 4'- progressively and smoothly adjust condenser 28, or resistance 21, or both, to provide the desired selectiveamplification. at the various track speeds.

In many cases it ispreferable to simplify the circuit 25 and its controlv byadjusting: resistance 21. to afixedsmall or zero value throughout the recordingjoperation; adjustment of; the capacity of? condenser: 2t alone being relied; upon. for ob taining the. desired compensation: for the. higher frequency components in. the rC01d8d WaV8;.

Fig; 3 shows a typical. family of" curves representing the: decibels of gain of amplifier 3 plotted against frequency for different adjustments of condenser: 26 when resistance 2} is: zero. The: utilized frequency range. may extend, for example, from 50 cycles to- 10,009 cycles per. second, but: maybe. more than this, or may be considerablyless.

Curve. '1. shows the gain; with. condenser- 26 at. its, zero value. wherein. the. compensation circuit 25. isopen, as in Fig; L, so that the negative: feed back action is at a substantially constant maxi mum value. throughout the utilized. frequency range, thus providing substantially distortionless transmission. of the waves through the amplifier, the amplification. being at. a: relatively low value. Curves U, V, W, X, show the; gain, respectively, when using the four successive values of the caparity of condenser 26, obtainedwhen. the shaft 42, Fig. 1, rotates in.'a clockwise directionv to connect, first, one condenser in. circuit, then two in parallel, then three, and. finally four condensers 25 in parallel, shunting the negative feed back coupling resistance [8. Condenser 26 obviously may be. made to change its value-as smoothly as desired, by making the stepssmaller, or by any 7 other well: known expedient.

The adjustment of. circuit 25 to give the substantially flat or distortionless amplifier characteristic, may be utilized for track speeds which are high enough to give satisfactory reproduction of the higher frequency waves, for example, for the range of track speeds within the. outer zone '1 of disk ID, Fig. 1. As the recording head 5 feeds toward the center of the disk, the speed progressively decreases through the zones T, U, V, W, X, cam 34 being so shaped as to progressively adjust condenser 26 and thereby adjust the transmission characteristic of amplifier 3, so that at any instant, the transmission characteristic is adapted. for the particular speed zone within which the waves are being recorded, as indicated by the use of similar letters on the curves and zones. V

Thereactance of condenser 26 is sohigh. at the lower end of. the utilized frequency range that the condenser acts as an open. circuit and has no substantial effect on the transmission level, whereas at the higher frequencies its reactance is so low that the condenser acts substantially as a. short circuit across. resistance i8. It is assumed for the purpose of. illustration,,.thatthe speed in zone U has decreased so low as to cause an appreciable loss of the higher frequency components. if. these components were all recorded in normal amplitude relation.- When recording in the zone U, thecondenser 25' is given such a value that at the predetermined point on thefrequency scale where. the higher frequency com: ponents begin to suffer attenuation of the kind indicated by the droop of the curves, Fig. 2, these components receive an extrav amplification or gain which increases with increase of frequency, thus giving a predetermined distortion to therecording current by making. the ratio of the. am-

aaaaczca plitude' of. the higher to: the; lower frequency waves. greater than in the. original waves;

In the successively lower speedi zonesV, W, X, the; point at which compensation begins, successively shifts; to lower: frequencies, thus widening the frequency range or band within which the higher frequency components are given an increased level. The: maximum. gain is. determined by the amplification obtainable. when the negative feedback coupling iszeffectively' short.- circuited by the low impedance; or neactance of compensation circuit 25. The upper limit of. gain is; preferably fixed at apredeterminedE value. to-limit'or prevent objectionable squeezing of the: reproducing stylus by the higher: frequency components, as men tioned above. This, upper limit of gainis shown by:- the: flat upper end; of the curves: in Fig. 3. The combination: of. negative: feed backwith the short circuiting effect. of circuit 25, prevents the gain from. exceeding the desired: value, butpermits of. obtaining againfor the higher frequency waves sufficiently above normal relatively to the gain: for. thelower frequency waves to insure of appreciable improvement in: the reproduction of thewaves;

The: curves in- Fig; 4- show the effect of varying theresistanceincivcuit 2 5; Curve V is: the same as-inFig. 3 and represents the decibels gain when the. capacity C of condenser 26* is used alone in circuit 25, with negligible or zero resistance. Curve C,.R1-,' shows the: gain when the value R1, ofresistance 2T is-appreciablew-h-ile the capacity C, of condenser 26: is the: same as with curve V. Curve C, R2, shows. the gain when'the resistance 21 is. increased in'value from R1 to- R2, while capacity C. stays. the same as with curve-V.

Increasing the resistance in this manner in cir cuit 25, widens. the portion of the frequency scale within which. there. is increased gain, and shifts to lower frequencies-the place where the gain curve starts: rising, thus adjusting the gain to compensate conveniently for the attenuation of higher frequency components. with decreasing track speeds. Increasing. the resistance. 21, also lowers the maximum gain at the upper end of each curve;v thus making, it possible conveniently to limit. the amount of stylus squeeze. The described eifect on curve V, of varying resistance 21- in series with one value of capacity 25, may be produced in a similar manner when using the other values of capacity corresponding with theother curves. Fig. 3..

I When manual control. of the transmission characteristicof amplifier 3 isdesired, instead of automatic control by rack. bar 28, the bar 28 may be removedv or'omitted, so that shafts 32 may be rotated manually,..or if. desired, plungers 3'! may be omitted, so that shafts. 42. may be rotated manually to. independently control. the. adjustmentsv of the impedance of compensation circuit 25.

The compensation circuit 25, Fig. 5; including variable. inductance 45,. variable condenser 25,

' and. variable resistance 21- in series, may be substituted' for the: circuit 25 in Fig, 1 or 7, and is particularly usefuk in cases requiring special attention to prevent squeezing or blocking of the reproducing stylus. Shafts 42', shown in dotted lines in Fig. 5,. control the impedance of circuit 25,. use being made of mechanism of the kind described. in connectionwith Fig. '1, so that adjustment of circuit; 25' at each instant corresponds with the. position of head 5- and the linear speed of the record-track, a separate cam 34 being provided for each; element 45; 2 6', 2T.

. flircuit 25, Fig; 5, is preferably tuned to have a resonance peak close to or slightly above the upper frequency limit of the utilized frequency range when the track speed is in the maximum speed range .T. The ratio of the amplitude of the higher frequency components relatively to that of the lower frequency components is thus made higherthan normal. The amplification of the higher frequency waves may then be progressively increased with decrease of track speed to compensate for the drooping of the high frequency ends of the curves, Fig. 2, until the higher frequency components tend to squeeze the space available as a path for the reproducing stylus, in the speed range V, for example. At this point there should begin an adjustment of the resonance frequency down the frequency scale under the control of earns 34, to minimize the stylus squeeze by gradually lowering the gain at the upper end of the frequency scale with decreasing track speeds, while components somewhat lower down. the scale which have less tendency to produce stylus squeeze, are given a gradually increasing gain or are only slightly changed in amplitude by the earns 34. Adjustment of resistance 2! alone, raises or lowers the level of the resonance peak. The described operations may thus produce a greater than normal ratio of amplitudes of high to low frequency components within a first range of track speeds, may increase this ratio in a lower track speed range, and then may decrease this ratio within a still lower speed range, while maintaining the ratio above normal relatively to the waves from the original source throughout the recording operations, so that some compensation is still obtained for the drooping current at the'upper end of the frequency scale at the lowest track speeds.

Fig. 7 shows a push-pull amplifier Aasimilar to the one tube amplifier A2 of Fig. 1, with similar reference characters applied to similar elements. It will be noted that resistance I1 is common to input circuits l4, l4, and output circuits I9, l9, while the negative feed back coupling resistances 18,18, individual to input circuits, l4, respec-' tively, branch away from resistance l1 and have their terminals remote from resistance ll, linked by the compensation circuit 25. Y

Circuit 25 is controlled by shafts 42 as in Fig. l. The push-pull form of circuit offers the usual advantages of push-pull operation over singletube' operation. A further advantage is that the compensation circuit leads are symmetrical with respect to the mid-points of the amplifier. The operation of the Fig. 7 circuit will be clear in view of the description'of Fig. 1 which operates in a similar. fashion.

Fig. 8 shows areproducing circuit, including the pick-up head 48 for reproducing waves recorded on the disk l0, and transmitting the waves through amplifiers A1, A2, A3, to the loud speaker LS. Amplifier A2 is of the negative feed back type, similar to that of Fig. 1 or Fig. 7, except that compensation circuit 25 includes the inductance coil 46 and the resistance 21, in this respect being similar to Fig. 5. Fig. 9 shows the decibels gain of amplifier A2, Fig. 8, over the utilized frequency range, The impedance or inductive reactance of the coil 46. at thev lowest used frequencies, is relatively low or negligible, and at the higher frequencies is so high as to act as an open circuit. The negative feed back at the lowest frequencies is thus reduced, but is unaffected at the higher frequencies. Consequently the amplification of the lower frequency waves isgreater than that 75 of the higher frequency waves, thus compensating for reduced low frequency amplitudes in the recording current. Where no such compensation is desired for the low frequency currents, the resistance 2! may be adjusted so high that the gain is substantially constant throughout the utilized frequency scale.

Fig. 10 shows the microphone or other source of waves l, transmitting current to the amplifiers 2and 4 in cascade, coupled with the recording head 5. The compensation control circuit 50, shunting the line between amplifiers 2 and 4, includes the resonant circuit consisting of the variable inductance coil 5| in parallel with the variable'condenser 5'22, in series with the variable resistance 53. By making circuit 5|, 52 resonant at a frequency, preferably at or slightly above the highest frequency in the utilized range, and adjusting resistance 53, by shafts 42, as in Fig. 1, a maximum amount of current is shunted from the line at the lowerfrequencies, so that the amplified current transmitted to the head 5, slopes up to a maximum at the higher frequencies. At low track speeds, the maximum shunting is obtained by reducing resistance 53 to a minimum. The resulting drain of current from the line, reduces the level of all the components to such an extent that potentiometer 54 isprovided in the line to restore the current level to its proper value, the potentiometer being automatically adjusted along with elements 5!, 52, 53, by shafts 42 and the other mechanism described in connection with Fig. 1. Control of coil 5i and condenser 52, permits of varying to some extent the ratio of inductive to capacity reactance and the slope of the compensation curve, without changing the resonant frequency.

It is thus possible with the Fig. 10 circuit, to partially, although not completely obtain recording current characteristics similar to curves T, V, X, Fig. 6. When shock excitation difficulties are to be avoided, the type of circuit shown in Figs. 1 and 7 is to be preferred. It will be noted that the Fig. 10 circuit requires at least four control shafts 42 and corresponding, associated mechanism, if each element 51, 52, 53, 54, is to be adjusted, as contrasted with only two control shafts 82 in Fig. 1.

While vacuum tube amplifiers have been disclosed in connection with the described circuits, it will be understood that linear amplifying devices of other types adapted to utilize negative feed back couplings, may be employed. It will also be understood that the wave transmission circuits, including the amplifiers and the controls therefor, may be applied to other uses than the recording and reproduction of waves. The recording head, while described as recording at progressively decreasingtrack'speeds, may record at increasing track speeds, as when the head is fed radially outward from the center of the record.

The invention is applicable, not only to disk records, but torecords of other types wherein the track speed varies or is so low as to interfere with suitable recording or reproduction of the higher frequencies or of components in some other partof the utilized frequencyrange. The .cam control mechanism may utilize cams of shapes designed for other purposes than those specifically mentioned. For example, in the case of sound recording or sound reproduction, cams may be employed with such shapes of contours as tovary the quality of the sound recorded or reproduced along the track, for special sound offacts. or novel sound quality. These and various other applications of the features of the invention will be understood to come within the broader aspects of the invention asset forth in theaccompanying. claims.

We claim:

1. The method of recording sound waves or other wavesin a record track at a relatively low, progressively decreasing speed along the track, which consists in recording said waves while subjecting them to a preliminary distortion, said distortion including the operation of progressively increasing the ratio of the amplitude of said waves within a higher frequency band to the amplitude of said waves in a lower frequency band until a predetermined increase in said ratio has been reached while the track speed decreases, and widening said higher frequency band without substantially exceeding said predetermined increase in ratio during said decrease of track speed. a 2. The method of recording sound waves or other Waves in a recordtrack at a progressively changing speed alongthe track, saidmethod including theoperation of recording said waves while subjectingthem to distortion, said distortion consisting of making the transmissionlevel of. certain of the higher frequency waves to be recorded greater than that of certain of the lower frequency waves to be recorded, progressively changing in one direction the level of certain of said higher frequency waves during a predetermined change of tracl; speeds and progressively changing in the opposite direction the level of at least a part of said higher frequency waves during a further change of tracl; speeds continued in the same direction beyond saidpredetermined change of track speeds.

3; The method of recording sound waves or other waves in a record track at different speeds along the track, which consists in recording said waves while subjecting the original waves to a preliminary distortion within a predetermined, first range of track speeds, saiddistqrtion including the operation of making the ratio of the amplitude of certain of the higher frequency waves to the amplitude of certain of the lower frequency waves greater than in theoriginal waves, and within a predetermined second range of track speeds below said first range, making said distortion less than in said; first rangebut greater than in the original waves.

4. The method of transmittingwavesto a recording head through a section of the wave path between the source of waves to be recorded and the recording head, while the speed of travel of therecording head along the record track, progressively changes, said method consisting of transmitting waves of difierent frequency through said section with substantially no distortion within a predetermined higher range of track speeds, making the transmission level of waves in a band of higher frequency relative to waves of lower frequency greater than normal within a second range of track speeds lower than said first mentioned speed range, andin a third range of track speeds lower than said second. speed range, widening said band and, making the transmission level of waves in said band greater than in said first speed range, butpreventing the transmission level of waves in said band from exceeding that in said second speed range.

5. In a system for recording sound in a record track at different speeds along the track, the

method of transmitting Waves through a section of thepath between the source of waves tobe recorded and the record track, said method consisting in transmitting waves of different. frequencies over said, section without distortion while recording within a first range of track. speeds, transmitting certain of the higher frequency waves over said. section at more than normal level relative to certain of the lower frequency. waveswhile. recording within a second ran e. of track speeds below said first range, and. transmitting certain of the higher frequency waves over said section at more thannormal. level relatively to said lowv frequency waves but .at a lower level than duringsaid second range, while the track speed is within a third range lower than said. second range.

6. In combination for. recording waves along a record track at relatively low speed, a wave recordinghead, and; an amplifier coupled with said; recording head for supplying theretothe waves to be recorded, said amplifier. having a negative feed back. coupling having a characteristic whichdecreases the-feed lbackJfor, waves in the upper part of. the utilized frequency range relatively to that for waves in the lower part .of said range.

7. In combination for: recording waves along. a record track at relatively low; speed, a; wave. recording head, and anamplifier coupledwith said recording head for supplying thereto. the waves to berecorded, said amplifier having a negative feed back coupling having. a charace teristic which decreases the feed back; in... the.

- upper part of the utilizedfrequency range-.rela: tively; to that of waves in the. lower. part. of

said range. said, coupling including. .a resistance and an impedance in. shunt with saidsresistance,

said impedance includinga capacity reactance element.

8. In combination, means for. tracing. a;.rela-. tively low speed wave record track, a. wave transf mission circuit coupled with said tracingmeans;

an amplifier insaid circuit, said amplifierhaving a negative feed back. coupling, said. couplingineluding a resistance in: series with;the.input .cir.- cuit of saidamplifier andan impedancein shunt with said resistance, .saiddmpedance having a r e y elective distortion; characteristic within the utilized frequency rangeof: said:;:am1-

plifier.

9.. In combination, means. for. tracingxa relatively-low I speed wave recordtrack, .a;wav.e :trans-. missioncircuit coupled with saidtraclngmeans, an amplifier in said circuit, said amplifier. .hav-

ing anegative feedback coupling, said coupling including a resistance in series with. theinput circuit, of said'amplifier and an impedancein shunt, with saidresistance; said. impedance. in-, cluding reactance ofonly onesign andhavinga frequency selective distprtion characteristic. with:

lathe-utilized frequency range-of said. amplifien;

10. In combination, means for: .tracing;a;,wa-ve record trackatrelatively low. speed, a wave trans-- mission 7 circuit for; said wave tracing means, an amplifier, in said circuit, saidampllfier having a negative feed back coupling, said coupling. hair-.- ing a frequencyselectivev distortion characterls tic within the utllizedfrequency:range-0t said amplifier, and-means. for changing the distortion characteristic, of saidscoupling in. timed. relation withchangesofsaldwtrack speed.

11. The method. of. recording sound waves-or. other wavesinza record. trackat arelatlvely low;

progressively changing speed along the said method including subjecting the original waves to a distortion, said distortion including making the ratio of the amplitude of components of said waves in a higher frequency band to the amplitude of components of said waves in a lower frequency band greater than in said original waves, changing said ratio inversely to change of track speed while the track speed is above a diminished value at which said ratio reaches a predetermined high value, keeping said ratio from 1 substantially exceeding said predetermined high value while the track speed is less than said diminished value, changing the width of said higher frequency band inversely to said change of track speed, and recording the resulting distorted 1 waves.

12. The method of recording sound or other waves in a record track at a relatively low, progressively changing speed along the track, said method including subjecting the original waves to a distortion, said distortion including making the ratio or the amplitude of components of said waves in a higher frequency band to the amplitude of components of said waves in a lower frequency band greater than in said original waves, changing said ratio inversely to change of track speed while the track speed is above a diminished value at which said ratio reaches a predetermined high value, maintaining said ratio at substantially said predetermined value while the track speed is less than said diminished value, changing the width of said higher frequency band inversely to said change of track speed, and recording the resulting distorted waves.

JACKSON 0. KLEBER.

LINCOLN THOMPSON.

CERTIFICATE OF CORRECTION. Patent No. 2,259,0Lp2. April 2.2, 19in.

JACKSON 0. KLEBER, ET AL.

It is hereby certified that the name of the as signee in the above numbered patent was erroneously written and printed as "The Sound Scriber Corporation" whereas said name should have been written and printed as -The SoundScriber Corporation, of Stamford, Connecticut, a corporation of Connecticut, as shown by the record of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same mayv conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of May, A. D. 19in.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents"

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