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`Oct. 10, 1961
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`E, F. HEMBROOKE
`IDENTIFICATION OF SOUND AND LIKE SIGNALS
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`3,004,104
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`Filed April 29, 1954
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`fr1000
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`AMPLITUDE FREQUENCY
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`PLZZhhhCZLLdahon
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`AMPLITUDE
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`FILTER re
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`23
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`—
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`__ANVENTOR
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`TRANSDUGER Ermil FrankHembrooke
`itMoniSolfo
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`ATTORNE
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`Sony Exhibit 1016
`Sony Exhibit 1016
`Sony v. MZ Audio
`Sony v. MZ Audio
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`

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`United States Patent Office
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`3,004,104
`IDENTIFICATION OF SGUND AND
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`LIKE SIGNALS
`Emil Frank Hembrooke, Brooklyn, N.Y., assiguor to
`Muzak Corporation, New York, N.Y., a corporation of
`New York
`Filed Apr. 29, 1954, Ser.No. 426,465
`6 Claims.
`(C1. 179—2)
`
`3,004,104
`Patented Oct. 10, 1961.
`2
`i
`quencies of the various components in a typical sound
`signal while the vertical scale represenst the amplitude
`of these various components at a particular instant of
`time. The audible frequency range of the sound signal,
`as indicated in this figure, extends approximately from
`20 cycles per second to 20,000 cycles per second.
`The amplitudes of frequency components of the signal
`over a very marrow range of frequency, for example,
`10. cycles per second, at some place in the frequency
`spectrum are attenuated, in accordance with the invention,
`This invention relates to a method and apparatus for
`in order to identify the signal. The attenuation of these.
`the identification of sound and like signals and particu-
`particular frequency components leaves a notch in the
`larly it relates to the identification of such signals when
`frequency curve as indicated by notch N in FIGURE 1.
`they are reproduced.
`:
`:
`The center frequency f, of this range of attenuation is
`An object of this invention is to provide for the posi-
`advantageously placed in that part of the frequency band,
`tive but unobtrusive identification of signals by impress-
`_for example, in the vicinity of 1000 cycles per second,
`ing upon them a characteristic code.
`that can be accommodated in even the cheapest repro-
`Other objects will become apparent or will be pointed
`out hereinafter.
`ducing systems since the permanence as an identifying
`mark of the attenuated harmonic components when so
`A particular advantage of the invention is that it pro-
`vides for the identification of recorded music or other:
`placed is greater than if frequency f, were placed at
`_ one édge of the signal frequency range.
`If it were placed
`audio signals by coded signals which are not evident to
`at one edge, for example, at approximately 20,000 cycles
`a listener but which nonetheless can easily be detected:
`pet second, the identifying effect could be entirely elim-
`and which are such an integral part of the audio signals.
`inated simply by filtering out all of the very high fre-
`that they are difficult if not impossible to obliterate.
`quencies of the sound signal.’ Moreover, in this regard,
`The unauthorized recording and rebroadcasting of
`the frequency f, should be placed at a frequency which
`musical performances, for example, has been difficult to
`is. generally present in the signal to be identified. This
`prevent because of the inability to detect positively
`frequency will of course depend upon thesignal, but for
`whether the rebroadcast is an exact reproduction of the
`music approximately 1000 cycles per second has been
`original or a different performance.
`The present inven-
`found to be satisfactory.
`tion makes possible the positive identification of the ori-
`the identifying “mark” is
`As shown in FIGURE 2,
`gin of a musical presentation and thereby. constitutes an
`discontinuous and eliminates the selected frequency com-
`effective means of preventing such piracy, ie. it may
`ponents of the signal only at certain intervals of time,
`be likened to a watermark in paper.
`according to a predetermined, coded pattern.
`.
`The invention may be used for the identification of
`FIGURE 3 shows a specific illustrative embodiment
`any kind of signal, whether audio, or other, comprising
`of a coding apparatus according to the invention compris-
`a number of different frequency components, although
`ing an electric circuit for impressing upon the signal
`for purposes of illustration it is shown and. described
`to be “marked” a code of the type illustrated in FIG-
`herein as applied to the identification of audio signals.
`URE 2. The audio signal voltage, comprising a number
`It is well known that a complex audio signal, such as
`of frequency components extending over a wide range
`mausic or speech, is composed of a number of frequency
`of frequency,
`is applied at
`input
`terminal 11. This
`components extending over a wide.range of frequencies.
`voltage is switched by means of an encoding switch 12-
`In accordance. with the. present invention such a signal
`either directly from terminal 11 to terminal
`13: or
`is identified by suppressing. a selected frequency, or nar-
`through a band-reject filter 14 to terminal 13, depend-
`tow band of frequencies, within the frequency spectrum
`ing upon whether the switch 12 is open or closed.
`.The
`of the signal at timed intervals according to a_predeter-
`switch 12 is opened and closed in sequence according to
`mined code. Because of the insensitivity of the ear in
`a predetermined coding pattern, for example, the name
`detecting the absence of a particular frequency or nar-
`of the orchestra or the trademark of the recording com-
`row band of frequencies in a sound signal, the identifying
`code will be imperceptible to the listener.
`pany may be spelled out in International. Code, or any
`other suitably identifiable sequence of pulses may be
`The suppression of a selected frequency or narrow band
`utilized as a proprietary code. The encoding switch may
`of frequencies is accomplished, in a specific embodiment
`be actuated mechanically, as by means of a coding cam,
`of the invention, by converting the signal into a complex
`so that the coding equipment is fully automatic and may
`electrical voltage and then passing this voltage through
`a very narrow band-reject electrical filter which passes
`be employed continuously at very slight expense. The
`band-reject filter 14 preferably has a very high “Q”—
`all but a very narrow range of frequencies in the complex
`voltage.
`that is, it is sharply tuned to reject only the frequency
`In the accompanying drawings:
`components within an extremely. narrow range on either
`FIGURE I is a graph of the spectrum of frequencies
`side of its resonant frequency, fp, so that the absence
`of the rejected frequency components will be imperceptible
`in a typical sound signal at an instant of time when a
`to the listener. This necessitates, of course,
`that the
`predetermined narrow range of frequencies is being sup-
`pressed;
`reduction in the total power of the audio signal due to .
`FIGURE 2 is a graph of the amplitude of the sound
`the deletion of said selected frequency components be
`signals in said predetermined narrow range of frequencies,
`less than approximately 3 decibels.
`The output voltage from terminal 13 may be broadcast
`plotted versus time to portray an illustrative coding se-
`quence;
`concurrently or it may be recorded and reproduced at.
`a later time, as illustrated in FIGURE 3, by means of.
`FIGURE3is an electric circuit, in block form, for im-
`a playback head, amplifier and speaker.
`pressing an identifying code on a signal in accordance
`with one embodiment of this invention;
`The code impressed on the signal by switch 12 will
`FIGURE 4 is an electric circuit,
`in block form, for
`serve to identify thereafter the origin of the audio signal
`so “marked.”
`detecting the identifying code.
`FIGURE 4 shows a specific illustrative embodiment
`In FIGURE 1 the horizontal scale represents the fre-
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`3,004,104
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`3
`of an apparatus for detecting the identifying code in
`the audio signal. This apparatus includes an input
`terminal 20 to which may be applied an audio signal
`voltage similar to that obtained at terminal 13 or ter-
`minal 13 in FIGURE 3. This voltage is amplified by
`means of an amplifier 21 and. fed through. a band pass
`filter 22, which has. a transmission. characteristic such
`that it. will pass only frequency components. within. the
`same. narrowrange of frequency: which the band-reject
`filter 14 will reject, as previously described.
`In other
`words, the transmission. characteristics of the band-pass
`filter 22: are substantially opposite to. those of the band-
`rejectfilter 14. The output of the band-pass filter 22
`is. connected.to a suitable transducer 23, such as a record-
`ing meter, oscilloscope, or the like. As the voltage ap-
`plied. to terminal 20 passes through the filter 22, all fre-
`quency components of the signal lying outside the pass
`band are eliminated and only those within this. band
`are passed. Since these frequencies were alternately sup-
`pressed: and’ passed by the encoding circuit illustrated in
`FIGURE3, the voltage applied to the transducer 23 will
`be intermittent.
`If transducer 23 is a recording meter
`containing a rectifier which converts these audio frequency
`alternating current voltages to direct. current voltages, it
`can plot a graph of their amplitude versus time. Thus,
`a graph of the type illustrated in FIGURE. 2 is plotted,
`in which the coding pattern, as indicated at 24 in FIG-
`URE 2, is readily apparent. Alternatively, transducer 23
`may be a loudspeaker to convert theidentifying code
`into sound.
`The foregoing is intended in illustration and not in limi-
`tation. Changes or modifications in the embodimentsil-
`lustrated will occur to those. skilled in the art and these
`changes or modifications may be made without depart-
`ing from the spirit or scope of the invention as set forth.
`- [ claim:
`1. In combination, an input terminal, means for sup-
`plying to said terminal an electric signal corresponding
`to an original signal and having a plurality of frequency
`components each having a respective frequency and am-
`plitude, an output terminal, encoding means for impress-
`ing a distinctive code on said electric signal for identi-
`fying the origin of said original signal, said encoding
`means including a narrow-band-reject filter adapted to
`attenuate said components of said electric signal within
`a very narrow frequency range, and also including a
`switch for connecting and for disconnecting said filter
`between said terminals in a predetermined time sequence
`to form said distinctive code.
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`2. A system of reproducing a continuous sound such
`as a musical selection and of permanently but unoh-
`trusively identifying its origin comprising: means for con-
`tinuously generating an electric. signal corresponding to
`said sound and having frequency components extending
`substantially over the audio range of frequencies, means
`for variably attenuating in accordance with an identifying
`code frequency components of said signal lying within.
`avery narrow band of frequency within said audio range,
`and means for then utilizing said identified electric signal
`whereby either said sound substantially in original form
`without. the audible presence of said. code or said code
`alone can be reproduced,
`3. The system as.in claim 2. wherein said means for
`utilizing includes. means for eliminating all frequency
`components of said electric signal except those remaining:
`in said narrow band.
`;
`4. The system as in claim 2 wherein said narrow band
`of frequency has a width of only a few cycles per second,
`and is near the center of said: band.
`5. A method of unobtrusively identifying a sound
`signal such as a musical selection, said methodcompris-
`ing the steps of taking a sound signal having frequency
`components within the audio range, and attenuating the
`components in a very narrow frequency band. within said
`range in accordance with an identifying pattern so that
`said signal will be permanently marked with an easily
`detectable pattern but a person hearing said marked:
`signal will be unaware of audible change in it.
`6. The method as in claim 5 wherein. said narrow: fre-
`quency band has a width of the order of ten cycles per
`second and lies in said audio range near a frequency of
`one thousand cycles per second.
`
`References Cited in the file of this patent
`UNITED STATES PATENTS
`
`1,724,938
`2,116,172
`2,335,335
`2,352,918
`2,376,275
`2,398,755
`2,406,034
`2,474,191
`2,503,701
`2,580,973
`2,636,936
`
`Jammer —_-_____________ Aug. 20, 1929
`Hyneman et al. -..---_-__ May3,. 1938
`Zenner —.----~--------— Nov. 30, 1943
`Smith2. July 4, 1944
`Rhoads ~..------.---.-. May 14, 1945
`Shepherd ~_..---.---_.- Apr. 16, 1946.
`Phelps _.-----_---_..--- Aug. 20,. 1946
`Reid et al. -202 June 21, 1949
`Baughman ~~... Apr, 11, 1950
`Sueur we Jan. 1, 1952
`Goldsmith —..---..-__ Apr. 28, 1953:
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`Sigaeg
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`pancetta!
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