US2315249A - Pseudo-extension of frequency bands - Google Patents

Pseudo-extension of frequency bands Download PDF

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US2315249A
US2315249A US414137A US41413741A US2315249A US 2315249 A US2315249 A US 2315249A US 414137 A US414137 A US 414137A US 41413741 A US41413741 A US 41413741A US 2315249 A US2315249 A US 2315249A
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signal
circuit
frequencies
tube
pseudo
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Rosa Louis A De
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/66—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission for reducing bandwidth of signals; for improving efficiency of transmission
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G5/00—Tone control or bandwidth control in amplifiers
    • H03G5/16—Automatic control
    • H03G5/18—Automatic control in untuned amplifiers
    • H03G5/20—Automatic control in untuned amplifiers having discharge tubes

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  • This invention relates to communication systems and more precisely to an improved system of pseudo-extension.
  • Pseudo-extension inv cludes, for the purposes of this invention, the methods and means wherein an audio signal, at 6 some point or at some time in its transmission either directly or indirectly to the ear, is modified so that, while all the composite frequencies present in the original. audio signal are not present in the signal ultimately transmitted to the .10
  • the auditory perception is of a sound which has substantially all the sonant characteristics of the original signal
  • a pseudo-extension circuit is defined as an electrical circuit'for the transmission of the lntelligence contained in a wide band of audio frequencies through a narrow band transmission channel; wherein the signal transmitted through the narrow band transmission channel is distorted by the addition to it of extraneous modulation and inter-modulation frequencies lying within the frequency range of said narrow band transmission channel.
  • One object of this invention is to provide a method and indicate means whereby signals which are modified and transmitted by a pseudo-extension" circuit are improved in quality and rendered more pleasing to the listener.
  • Another object of this invention is to lessen unwanted and extraneous percussive and rasping sounds introduced in a signal by the "pseudoextension" process of the present art.
  • Another object of this invention is to reduce the apparent auditory distortion resulting when 5 a transmitted'signal of transient nature is modified by theaction of a non-linear transducer.
  • Another object of this invention is to reduce the apparent auditory distortionresulting from the inter-modulation of at least two signals at least one of which is transient in nature.
  • Figs. 1 to.'7 show a single frequency signal of a transient nature and the approximate frequency spectrums existent at various stages of the signal.
  • Fig. 8 shows a diagrammatic circuit of one embodiment of the invention as incorporated in a pseudo-extension non-linear circuit.
  • Fig. 9 shows, diagrammatically,- an alternate circuit which may be employed to utilize the advantages of the invention.
  • Fig. 10 shows, schematically, a simplified ciracter.
  • a t Fig. 11 illustrates a circuit including a frequency selective feed-back circuit-used to accomplish the object of this invention.
  • Fig. 12 illustrates an embodiment of this in-' vention 'to retain or even accentuate the percussive quality of'a signal.
  • Fig; 13 shows, in'block diagram form, the use] of the circuits of Figs. 8 to '12;.with associated a apparatus in an improved pseudo-extension" system.
  • Fig. 1 shows such a wave.
  • Fig. 1 is shown an arbitrary single frequencysignal wave. having a transient char- A single frequency is shown for con I venience since by super-position of a plurality of frequencies',"signals of the typ generally encountered infthe transmission; of audible sounds can'be obtained.
  • This signal may be regarded as a single frequency only insofar as frequency is measured by the reciprocal of the time between adjacent peaks of the same, polarity.
  • every change in amplitude hasassociated with it an infinite number of side bandaprovided that the intervals between amplitude changes are infinitely long. While this is the idealizedcase, nevertheless the side-bands encountered in practical cases may extend to the tenth harmonic of the fundamental frequency particularly in sharplyintroduced low frequency waves.
  • the side-bands would contain all frequencies or would be a continuous spectrum; In other words, as the steady state interval approached infinity, the prime factor ofthe sideband frequencies would approach zero as a limit.
  • An analysis of a practical case may be made by assuming. that the single frequency is amplitude modulated by a frequency modulated signal, wherethe frequency modulation is the variations in the intervals between successivechanges in amplitude. Therefore, in the practicalgcase the prime factor of the side-band'frequencies-is the reciprocal of the time betweenthe longest in- 2 Y l I 2,315,249
  • the side-bands are. grouped about the steady state frequency Qf'the wave and their amplitudes are an inverse function of their displacement from frequency f.
  • This invention describes definite methods and means for reducing the distortion encountered in prior art pseudo-extension processes.
  • the circuits describedhereinafter may also, with resulting improvement, be used in place of the nonlinear circuit elements of the pseudo-extension system described in the applicant's co-pending U. S. application No. 348,359, filed July 30, 1940.
  • the resulting frequency spectrum at time h which appears in'the output of the non-linear device is similar to that shown in Fig. 2 except that, due to the resulting inter-modulation products, the magnitudes of the side-bands are greatly increased; in other words, the spectrum is similar to that obtained if the original wave had been building up more rapidly at that time.
  • the effect on the listener hence, is that of a signal building up more rapidly and sharply than the original signal of Fig. 1 warranted.
  • Fig. 7 shows the spectrum analysis at time t1 when the wave amplitude is approaching a practical zero value. 4 l
  • prior art pseudo-extension circuits include as an essential element, a non-linear transducer.
  • This non-linear transducer may be a square law detector, a class "0 amplifier tube. a combination of both, or any circuit having a non-linear input vs. outputcharacteristics.
  • non-linear device will produce an exaggerated transient quality which persistsafter the transient quality of the original signal has been removed.
  • the non-linear device a At tlmett the output er the non-linear device a will have a frequency spectrum in which the sidebands are of much greater amplitude than indicated by Fig. 6.
  • Fig. 8 shows, diagrammatically, one 'circuit which may be'used to accomplish the object of The input signal is impressed across the terminal marked-Elna
  • This signal if the pseudoextension isto be applied mainly to the bass frequencies; is preferably applied to the thru a low pass filter F.
  • a low' pass filter of one section prototype constant K type having a cutoff frequency of aboutlOO cycles has been found satisfactory.
  • the output of the filter is divided into two paths, the one to the left and consisting of C1; R1; R2; T1; R and C5 being the non-- linear circuit; andthe, lower path, consisting of CajRa; R1; C4; R5; andTz is the control circuit.
  • the purpose of this control circuit is to.
  • the cathode and control T2 isbiased by means of indicatedon the dia- Thistime lag is a function ofithe product of R and C, for increasing signals, and a function of the product R4 and C4 for decreasing input signals.
  • the point where, on the increasing amplitude envelope of theinput signal the tube T2 begins to conduct can be adjusted by the setting of the potentiometer R3.
  • the rate at which the rectified signal across Ri decays when the input sigcircuit is supplied by the bat-' eifect is again exaginput capacity of tube T1 may be made small in comparison to the time constantso; R5 C4 and R4 C4 so that these latter consta'ntswill'detern'iinev the build-up and decay respectively of the voltage applied tothe gridci tube T1 from the plate circuit of tube T2.
  • the tube T1 operates as a linear device until the input signal hasreached a relatively steady-state conditionwhere after the tube ,Troperatesas a nonlinear device and continues to do so until a dee cay transient occurs inthe input signal at which time the tube T1 again operates as a linear ampliher.
  • the time constants of the delay circuits must be chosen with a view to the frequencies which are being impressed on the tube T1. Experimentally'it has been found-that satisfactory results are obtainable when the delay between the onset of the signal and the operation of T1 as a nonlinear device is, as a function of the. mean frequency applied to the grid-of ,tube T1, approximately 20 milliseconds for 200 cycles per'second 40 milliseconds for 100 cycles per second;
  • the tube T1 should preferably be returned to its linear operation as soon" 'as the decay transients set in; an approximate time being 8 to l0 milliseconds.
  • FIG. 9 Another embodiment of this invention is shown in Fig. 9. This circuit accomplishes the object of this invention in one possible alternate manner.
  • the signalto be pseudo-extended is ap- ⁇ plied to the input of thefilter F. This filter may.
  • the rectified signal appearing across R4 is apof .the tube T1.
  • a voltage across R4. is essentially a non-distorting linear amplifier.
  • a positivevoltage appearing across R4 will destroy the bias of tube Trand cause it to operate as a grid leak detector or square law non-linear amplifier.
  • the battery Em is selected so that the'operation of tube T1 in the of the filter F isapplied by means of the'condenser Cs and the grid resistor R1 to one control grid of a two control grid pentode T3.
  • the amplified signal appearing in the plate circuit of Ta is impressed by means of the condenser C7 to the level of the signal at the grid of T4 being adjustable by means of the potentiometer R3.
  • Theamplified signal appearingin theplate circuit of T is applied through the audio transformer Tm to a double diode rectifier T5.
  • a rectifiedsignal appears across the-diode load-resistance R1, the rate at which it builds up being determined by the product of'the series re- 4 sistor Ru and the capacitor C4.
  • This rectified voltage is s'ppliedto the second control grid of Ta and being a negative voltage, decreases the transconductance of ".thetube Ts resulting in a decrease in series, between one terminal of the secondary f the transformer and the control grid of tubeTi.
  • the bias of :tube T1- is adjusted so that tube T1 acts as a non-linear device when the amplitude of the input signal to the compressor circuit has reached an amplitude beyond which further-increases are minimized.
  • the selection of the time constants associated with'the diode load should be chosen so that the ripple voltage appearing across the diode load and applied toits associated grid of T: is approximately tenper' cent of the signal voltage applied to the other grid of Ta. This condition holds for the charging time of C4 through Rs andthe associated closed circuit and for discharg'etime of 04 as determined by the value of R4, and-the equivalent shunt impedance across C4 due to. the associated shunt meshes.
  • the output voltage limit is taken from the plate circuit load resistor R0 through the blocking condenser Cs.
  • circuits of Fig. 8 and Fig. 9 show twoembodiments of the invention, and in addition they illustrate two difierent solutions to the problem of the elimination of transient distortion in a nonlinear device. f
  • the first circuit that of Fig. 8 varies the linearity of the non-linear device so thatit operates essentially as a class A amplifier during the time that a transient is impressed on its 1nput.
  • the second circuit arrangement that .of 1"ig. 9, is illustrative of that class of circuits within the scope of this invention wherein the transients are minimized at those times when the non-linear device operates as such.
  • nal in the output of the transducer is very slow. In other words, a sharply increasing or decreasing amplitude will not be effective as such in the output of a transmission network having a narrow frequency acceptance band.
  • the signal to'be impressed on the This tube is arranged with a i non-linear device of a "pseudo-extension circuit is designated at E111.
  • This signal is divided'into two channels, the first of these is applied through the volume control. R1 to one control grid of a mixertube-such as the present day 6L7, desig-'
  • the other channel is vapplied to a fitted as T13, tuned circuit Tc tuned to the region of the frequencies which are to be pseudo-extended.
  • T13, tuned circuit Tc tuned to the region of the frequencies which are to be pseudo-extended.
  • the narrow band output of the tuned circuit To is amplified by ,a linear amplifier designated operate, by virtue ofthe initial bias, as a classA amplifier for small signals applied'to its grid.
  • the volume control Rule adjusted so that the signals appearing at the grid of T1 via the first channel, that is. impressed on the first control grid. 01 of Tn, are of sufliciently low magnitude so as to be amplified by T1 without distortion.
  • This signal by circuit design. is made approximately ten times the magnitude 'of the, first channel signal impressed on the grid of T1.
  • the tube T1 therefore. acts as a non-linear device in the presence of a signal from the second channel.
  • circuit of Fig. 10 described above and the circuitof Fig. 11 to be described operate to prefrom the harsh, rasping, spuriously fricative soundsassociated with prior art pseudo-ex tended signals.
  • Fig. 11 illustrates a circuit which may be used to realize the utility of this invention. Basically, its operationis similar to that of Fig. 10 but it is shown in order to indicate one of a large number of modifications which are within the scope of If the low frequency spectrum this invention, and whichutilize the method and means described herein. I
  • Ein' is an audio signal containing the frequencies which are to be pseudoextended.
  • This signal Em is applied to one grid G1 of a two control grid pentode T14 of the present day 6 L7 type.
  • R1 is the grid resistance to maintain the bias on grid G1.
  • the tube is biased so as to operate as a linear amplifier by the conventional self-biasing by-passed cathode resistor arrangement as indicated in'the figure.
  • An amplified signal appears across the plate load resistor R20 of tube T14. Those frequencies appearing in this amplified signal which are to be pseudo-extended are fed-back through the blocking condenser C11 and the network R23, C13, R22, C12 to the second grid G2 of the tube T14.
  • the network 1223,013, R22, 012 is selected so as to produce an approximate phase shift-of 180,degrees for these frequencies.
  • the potentiometer is used to control the voltage of the fed-back signal so as to prevent oscillation.
  • the phase .of this fedback signal being such that regeneration will occur for frequencies to be pseudo-extended, the tube T14 will therefore selectively amplify these frequencies to a much greater extent thanother frequencies present in the signal Em.' Effectively therefore the tube T1; acts as a tuned amplifier having'a maximum gain in the neighborhood of the frequencies to be pseudo-extended.
  • the principle of operation of the circuit of Fig. and that of Fig. 11, is similar, that is, in Fig. 11, due to the relatively sharp frequency characteristic of the tube T14 and its associated feed-back circuit, the side-bands present during changes in amplitude of the preferentially amplified signal are limited in amplitude.
  • the signal appearing across the plate load resistor R is impressed, through the blocking condenser C11 to the potentiometer R1.
  • the setting of the potentiometer is adjusted so that. in absence of a regenerated signal across its terminals, the ordinarily amplified voltage is insuflicient to drive the tube T1 oil.”
  • the linear portion of its grid voltage-plate current characteristic as determined by the grid bias produced by the oath- Fig. 12 shows, diagrammatically an arrangement of a circuit utilizing the novelty of this invention which may be used to retain the or even augment the transient quality of asignal and yet avoid the "harsh and fricative sounds due tothe prolongment of thetransient stateof a signal due to the action of anon-linear trans-' ducer.
  • the signal Em to be pseudoextended is impressed on the input of thefilter section
  • This filter section may be a sin-' 1 vgle stage constant K prototype or its'equivalent.
  • the filter F is arranged as a. high pass, a representative cut-off frequency being 3000" cycles. If the circuit is to operate for. base frequencies, the filterF may be a low pass having -a cut-off frequency of about 120 cycles.
  • the output of the filter Fin either case is impressed on the grid of a .linear amplifier tube Ts, R1 being the conventional grid resistor as-.
  • the amplifled signal appearing in theplate circuit of tube To is divided into three channels consisting of two control circuits and one main circuit.
  • the main circuit by means of the transformer TR; having twosecondary windings, is further divided into two secondary circuits.
  • a amplifier'tube T1 appears ode resistor R24 bypassed by the condenser C14.
  • the tube T1 When a regenerated signal is present however, the tube T1, dueto the much larger voltage of this signaL'will, and aided in this direction by the grid'resistor' Rz, act as a non-linear device and produce inter-modulation and harmonic 7 components in its plate circuit.
  • the signal appearing across the plate load R18 is utilizable in place of the output of the non-linear'device of the related prior art circuits.
  • the augmented transient sidebands due to the inter-modulation frequencies are introduced by the tube T12 during the interval wherein its grid has a zero bias with respect to its cathode.
  • the negative voltage [appearing at the junction of R9 and R10 and applied through R13 to the grid of T12 establishes a negative bias on this grid and causes the tube T12 to act as a linear or class "A" amplifier.
  • the signal appearing in the plate circuit of the tube T12 is then applied to the output through the audio transformer TRs.
  • the upper control circuit consisting of R11, T9, TR4 and T10 controls the grid bias of the tube T11.
  • the tube'Tn is biased by the battery Ect so as to operate, in the absence of a voltage across the load resistor R15 of the rectifier T10, as a linear or class A" amplifier.
  • the input signal Em When the input signal Em is suddenly applied, it is amplified by the tube T6 and that portion of it appearing on the grid of T9 is amplified further, and, by means of the audio transformer TR4, is applied to the diode T10 through the rectifier load impedance R14, C10 and R15.
  • the condenser C10 charges slowly through the limiting resistor R14 and as it charges, the potential of the cathode of the rectifier T10 gradually rises with respect to ground.
  • the cathode is connected through the battery E04, the upper secondary winding of the transformer TR: and R12, to the grid of the tube T11. Consequently as the cathode 01 T10 rises in potential in a positive direction, the voltage of the battery E ⁇ is gradually counteracted and the negative bias of the tube T11 is gradually destroyed. As the bias of T11 is destroyed the grid operates with too little bias and finally without bias so that the tube T11 will operate as a nonlinear device similar to a grid leak detector. R12,
  • a resistance in the grid circuit provides an additional voltage drop across it when, on the positive halves of the main channel signal, grid current flows in the grid circuit or the tube T11. This action biases the grid more heavily at these times and accentuates the non-linearity.
  • Apower amplifier with an associated filter is connected across the secondary winding of TRs.
  • the characteristics of the filter should approximate the frequency characteristic of the limited i'requency acceptance band of the apparatus through which the pseudo-extended signal is to be transmitted.
  • To the output terminals of the power amplifier and filter is connected a loud speaker.
  • This auxiliary apparatus is shown on rug.- 12 by the dotted lines, PA being the power amplifier, Fx beingthe filter and LS being the loud speaker.
  • the vertical plates of a cathoderay oscilloscope are connected between the plate of T11 and ground.
  • a monotone signal whose frequency lies approximately midway in the frequency band of the signal which is to be pseudo-extended is abruptly applied and removed intermittently to the input Em of the circuit of Fig. 12.
  • the setting of Ru and the value of the variable resistance R14 are adjusted simultaneously to a point where while the cathode ray oscilloscope deflection appears to be unilateral, sharp clicks are not heard in the loud speaker upon the application and removal of the input signal.
  • this invention provides methods and means for producing a pseudo-extended signal which is relatively exaggerated and prolonged transient quality apparent as distortion, these unpleasant sounds suddenly applied tothe input (Em) an ampli-' I fied signal containing a plurality of side-bands appears in the plate circuit of T12. (Also, during the first instant, an amplified undistorted signal appears in the plate circuit of T11. These signals are combined in the transformer TR: and are available across the output terminals of TRs. Gradually, after the first instant, the plate circuit signal of T1: becomes undistorted, as a negative potential builds up across R10 and Co; at which time the plate circuit signal of T11 is still relatively undistorted sincethe condenser Cm is still only. partially charged.
  • the signal Emit is therefore relatively undistorted for an interval after the first, after which, when C10 has charged sufficiently to cause the voltage across it to counteract the initial grid bias of T11, the plate circuit signal of T11 becomes distorted producing intermodulation between harmonic components of those. frequencies impressed on its grid.
  • a sound having a wide audible frequency spectrum may be transmitted to a listener over a transmission link having a narrow frequency pass characteristic, and while the sound reaching the listener's ears does not contain a wide band of audible frequencies, nevertheless, the effect is substantially the same as though all the audible frequencies contained in the original sound were available, without distortion, to the listener.
  • Fig. 13 shows, in block diagram form, since the elements thus shown are well known to the art, the utilization of this invention to one of many possible and varied applications.
  • the system of Fig. 13 shows the use of themethod and means oithis invention to the transmission of sounds by a radio system.
  • S is a source of audible sound as for example an orchestra.
  • the sounds emanating from this source are intercepted by the microphone and after conversion to an elec- I area 7 m,
  • the output of theam. plifier AMP] is considered as the' input Em of the 1 representative circuits. of Figs. 8., to 12,shown herewith.
  • the. circuit means of: this invention After. being ,modified by, the. circuit means of: this invention; the resulting output signal Eout 'is impressed and'used to modulate a radio frequency carrier; in the usual manner in the radio transmitter'XT.
  • Figs. 8 to 12 may be used similarly to thoserecogni' zed as prior art circuits, yie lding;in the place of the latter an improved and undistorted result. Obviously, therefore, thesecircuits and the principles gov erning their. operation can be used in conjunction with: the:;consonator ⁇ -circuit described in my co-existing application no frequency limitations in the transmission link f but restricted,side-bandradio transmission is desired,ythe,filter Fm of Fig. 13 may be interposed 'in the transmittercircuit.
  • the processor pseudo-extension need not be limited so as toobtain a signal containing as an example frequencies from, 120 cycles tov 10,000 cycles per second andbetween'which limits are included the intermodulation and harmonic-produ g evident to-persons familiar with. the pertinent art, without depart- Other embodimentswill be ing fromthe spirit or scope of my invention.
  • non-linear device and; a source of audio fre- I the non-linear device, means for varying the non- ,linearity of said non-linear device during changes ucts .of frequencies lower than 120 cycles; nor
  • the middle register of a signal that is, those frequencies in a signal fallingwithin the narrow acceptance band of a transmission link may be operated upon bythe proceduredisclosed herein and a more pleasant and'more quency modulation meansior .impressing said audiofrequency modulations upon the inputof in the amplitude of the impressed signal, means for collecting at leasta part of the-output of said non-linear device,- and means fortransmitting the collected signal.
  • non-linear device and a source of audio frequency modulations means for dividing the audio frequency modulations into two channels, means for selecting a part of the frequencies contained in the first of-these two channels, means for realistic signal will result.
  • these latter frequencies are operated upon, the, resulting signal isgiven more sonority and fullness, similar to'an eifect produceable by increasing the amplitude of a sound to loudinten'sitles.
  • fmeans for combining the output signal of said non-linear device with the signal of the second of the two channels, and means for transmitting at least apart of the combined signal.
  • a method of increasing-the apparent frequency range of a transmitted audio signal comprising the steps of selecting at least apart of the audio signal modulations, limiting thechanges in amplitude envelope of the selected signal by the action.of a compressor circuit so as to produce substantially a constant amplitude frequency distortionless signal, impressing the thus limited audio signal on the input of a nonlinear device, and collecting and transmitting at leasta part oithe output of said non-linear device.
  • a method; of increasing the apparent free I quency range of a transmitted audio signal comprising the steps of: selecting at least a part of the audio signal modulations, limiting the' changes in amplitude of the selected signal by the action of a compressor circuit, impressing the together with the collected and transmitted part of the output of the non-linear device.
  • a method of increasing theapparent frequency range of a transmitted audio signal comprising the steps of selecting at least a part of the audio signal modulations, increasing the relative amplitude of a portion of the frequenciescontained in said selectedpart, impressing the distorted signal thus resulting on the'input 01. a non-linear device, and collecting and transmitting at least a part of the output signal of said non-linear device.
  • a method of increasing the apparent frequency range of a transmitted audio signal comprising the steps of: selecting at least a part of the audio signal modulations, increasing the relative amplitude of a portion of the frequencies contained in said selected part, impressing the resulting distorted signalon the input of a nonlinear device, varying the degree of non-linearity of said non-linear device during changes in amplitude of the original audio signal, and collecting and transmitting at least a part of the output signal of the varied non-linear device.
  • a method of increasing the apparent frequency range of a transmitted audio signal comprising the steps of: dividing the audio signal into two channels, impressing the first of these.
  • the combination with a non-linear device comprising means for varying the non-linear characteristic of said non-linear device during the times whenthe signal impre'ssed'on the input oi'said non-linear device is undergoing a change in its amplitude envelope.
  • the combination with a non-lineardevice comprising means for impressing an audio signal upon the input of said non-linear device, means for vary- LOUIS A. Di: ROSA.

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US414137A 1941-10-08 1941-10-08 Pseudo-extension of frequency bands Expired - Lifetime US2315249A (en)

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GB7819/47A GB682233A (en) 1941-10-08 1947-03-21 Improvements in or relating to electrical circuits for the production of subjective auditory effects

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3075044A (en) * 1958-05-05 1963-01-22 Tonalyzer Inc Method and apparatus for obtaining sound
US4150253A (en) * 1976-03-15 1979-04-17 Inter-Technology Exchange Ltd. Signal distortion circuit and method of use
WO1998046044A1 (en) * 1997-04-04 1998-10-15 K.S. Waves Ltd. Apparatus and method for bass enhancement
US6285767B1 (en) 1998-09-04 2001-09-04 Srs Labs, Inc. Low-frequency audio enhancement system
US7031474B1 (en) 1999-10-04 2006-04-18 Srs Labs, Inc. Acoustic correction apparatus
US20080022009A1 (en) * 1999-12-10 2008-01-24 Srs Labs, Inc System and method for enhanced streaming audio
US8050434B1 (en) 2006-12-21 2011-11-01 Srs Labs, Inc. Multi-channel audio enhancement system
US9236842B2 (en) 2011-12-27 2016-01-12 Dts Llc Bass enhancement system
US9258664B2 (en) 2013-05-23 2016-02-09 Comhear, Inc. Headphone audio enhancement system

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3075044A (en) * 1958-05-05 1963-01-22 Tonalyzer Inc Method and apparatus for obtaining sound
US4150253A (en) * 1976-03-15 1979-04-17 Inter-Technology Exchange Ltd. Signal distortion circuit and method of use
WO1998046044A1 (en) * 1997-04-04 1998-10-15 K.S. Waves Ltd. Apparatus and method for bass enhancement
US6285767B1 (en) 1998-09-04 2001-09-04 Srs Labs, Inc. Low-frequency audio enhancement system
US7907736B2 (en) 1999-10-04 2011-03-15 Srs Labs, Inc. Acoustic correction apparatus
US7031474B1 (en) 1999-10-04 2006-04-18 Srs Labs, Inc. Acoustic correction apparatus
US20060126851A1 (en) * 1999-10-04 2006-06-15 Yuen Thomas C Acoustic correction apparatus
US7987281B2 (en) 1999-12-10 2011-07-26 Srs Labs, Inc. System and method for enhanced streaming audio
US20080022009A1 (en) * 1999-12-10 2008-01-24 Srs Labs, Inc System and method for enhanced streaming audio
US8751028B2 (en) 1999-12-10 2014-06-10 Dts Llc System and method for enhanced streaming audio
US8050434B1 (en) 2006-12-21 2011-11-01 Srs Labs, Inc. Multi-channel audio enhancement system
US8509464B1 (en) 2006-12-21 2013-08-13 Dts Llc Multi-channel audio enhancement system
US9232312B2 (en) 2006-12-21 2016-01-05 Dts Llc Multi-channel audio enhancement system
US9236842B2 (en) 2011-12-27 2016-01-12 Dts Llc Bass enhancement system
US9712916B2 (en) 2011-12-27 2017-07-18 Dts Llc Bass enhancement system
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US9866963B2 (en) 2013-05-23 2018-01-09 Comhear, Inc. Headphone audio enhancement system
US10284955B2 (en) 2013-05-23 2019-05-07 Comhear, Inc. Headphone audio enhancement system

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