`Exhibit
`
`1 12 8
`
`0
`4,224,773
`[11]
`[19]
`United States Patent
`
`Elkins
`[45]
`Nov. 7, 1978
`
`[54] AUDIO STORAGE AND DISTRIBUTION
`SYSTEM
`
`Attorney, Agent, or Firm—Duckworth, Hobby, Allen &
`Pettis
`
`[76]
`
`Inventor: Robin Ellkins, 5641 NW. 28th St.,
`Lauderhill, Fla. 33313
`
`-
`
`[21] Appl. No" 744,966
`.
`_
`Nov. 26’ 1976
`[22] Filed
`[51]
`Int. Ci.2 ............................................ H04M 11/00
`[52] US. Cl.
`................................. 179/2 A; 179/2 DP
`[58] Field of Search .................. 179/2 R, 2 A, 2 DP,
`179/} B, 1 FS, 1 13’ 15.55 R, 15.55 T;
`340/1725, 347 AD, 155 GC, 15.5 TS
`‘
`
`[56]
`
`References Cited
`U S PATENT DOCUMENTS
`'
`'
`10/1967 Marill ................................ 179/2 DP
`3,347,988
`5/1969 Doug“
`179/2 DP
`3,444,324
`
`
`P3111115 ..
`' 340/347 AD
`5/1969
`3,444,550
`
`::
`22:222
`
`325/30
`6/1971
`Ragsdale ..
`£590,381
`7/1976 Wermuth .......................... 179/1 P
`3369:6220
`Primary Examiner—Kathleen H. Claffy
`Assistant Examiner—Joseph A. Popek
`
`ABSTRACT
`[57]
`This invention relates to an electronic system and a
`method for storing and distributing audio signals over
`existing communication lines. The system comprises a
`compressor for compressing in a predetermined manner
`the waveform amplitude of an input analog signal,
`thereby forming a compressed analog signal The com-
`Pressed analog signal is the“ converted into a digital
`signal by an analog to digital converter. A digital inter-
`face subsystem stores and retrieves selected ones of the
`digital signals for transmission over a communications
`line. At a remote end of the communications line the
`
`digital signal is converted back to its analog compressed
`signal representation by a digital to analog converter.
`The compressed analog signal is then expanded in a
`manner complimentary to the compressor operation,
`thus reconstructing the analog signal. A selector gener-
`ator is provided at the remote end of the communica-
`. man
`communications line to command the digital interface
`SPbSYlStem to 5316“ the €165th one Of the Stored digital
`Signa s.
`
`12 Claims, 1 Drawing Figure
`
`
`
`(25
`I30
`V ______ _I
`DIGITAL
`ANALOG TO
` DIGITAL CONV
`COMPRESSOR
`
`STORAGE
`
`
`
`
`
`
`ANALOG
`ANALOG TO DIGITAL
`
`
`CONVERTER
`SOURCE
`
`
`
`
`
`
`88
`AUDIO
`AMPLIFIER
`
`9
`
`-3
`
`37
`
`
`87)
`DB
`60
`I
`DIGITAL TO
`
`
`ANALOG COVV.
`
`
`
`
`SECOND
`DIGITAL
`
`
`
`STORAGE II
`
` DIGITAL TO ANALOG
`DIGITAL
`:1
`
`
`INTER’FACE
`SUB SYSTE VI
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` 78
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`CONVFRTER
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`K
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`92
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`

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`US. Patent
`
`Nov. 7, 1978
`
`4,124,773
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`1
`
`4,124,773
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`AUDIO STORAGE AND DISTRIBUTION SYSTEM
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to audio storage and distribu-
`tion systems, and in particular to digital communication
`systems which may be remotely controlled from a plu—
`rality of user locations.
`2. Description of the Prior Art
`The present state-of-the-art audio distribution sys-
`tems may be classified into two general groups. The
`first type of audio system utilizes a central source of
`audio programming which transmits a sequence of
`audio program material over a master communications
`distribution system to a plurality of user locations. The
`user has no control over the sequence of the audio pro-
`gramming other than to adjust the volume, to change
`channels or to turn the programming on and off. The
`MUZAK music subcarrier system authorized by the
`Federal Communications Commission is one common
`example of this type of audio system.
`A second type of audio system employs a master
`control center having a plurality of available audio
`program material which may be selected and sequen-
`tially arranged from a user center located nearby. In this
`second type of system the user may select and sequen-
`tially arrange several of the available programs. How-
`ever, the communications requirements of this second
`type of system generally limits the separation between
`each of the user stations and the master control station
`to a relatively small geographic area. A common exam-
`ple of this type of system is the remote controlled audio
`system utilized by libraries or large universities to dis-
`tribute audio program material
`to various remotely
`located student centers.
`In contrast, the present invention uses a master data
`bank located at a central location which is coupled to a
`plurality of user locations by common communication
`lines, such as narrow band or wide band telephone lines.
`Special signal processing is accomplished both before
`the signal is transmitted over the lines and after the
`signal is received at the user location to optimize the
`signal quality to suit the particular limitations of the
`communications system. Each remotely located user
`position also includes a command section for generating
`a command signal over the communications line for
`being received at the central data location for selecting
`the desired sequence of the stored programs.
`The prior art contains several examples of the type of
`technology required to implement
`this system. Von
`Muench in U.S. Pat. No. 3,626,096 discloses the use of
`a microphone coupled to an analog to digital converter
`for digitizing the analog signal. Palus in U.S. Pat. No.
`3,444,550 discloses a system utilizing a logarithmic am-
`plifier driving an analog to digital converter. Digital
`data transmission systems (MODEMS) of the type dis-
`closed by Forney et al. in U.S. Pat. No. 3,887,768 and
`Ragsdale et al.
`in U.S. Pat. No. 3,643,023 are well
`known in the art.
`
`SUMMARY OF THE INVENTION
`This invention relates to an audio communications
`system for transmitting analog signals over communica-
`tions lines. The system includes compressor means such
`as a logarithmic amplifier, for receiving the analog sig-
`nal and processing the analog signal in a predetermined
`manner to match the input of an analog to digital con-
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`verter means, which is provided for converting the
`processed analog signals to a digital signal. Digital inter-
`face means are provided for storing, retrieving and
`retransmitting the digital signal over the communica-
`tions line. Digital to analog converter means are pro-
`vided for receiving the digital signals from the commu-
`nications line and converting the digital signals to the
`analog signals. Expander means are provided for ex-
`panding the waveform amplitude of the compressed
`analog signals in a predetermined manner for recon-
`structing the original analog signal. In a first preferred
`embodiment command means are provided for generat-
`ing a command selection signal which is transmitted
`over the communications line from the remote location
`to the digital innerface means for selecting one or more
`of the digital signals thereon for being retrieved and
`retransmitted.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Other objects, features and advantages of the present
`invention will be obvious from a study of the written
`description and the FIGURE which represents a sche-
`matic block diagram of a first preferred embodiment in
`accordance with the present invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`A first preferred embodiment of the present invention
`is illustrated in the schematic block diagram of FIG. 1.
`The source of the analog signal, shown generally as 20,
`may be obtained from various components such as mi-
`crophones, tape recorders, disc reproducers, etc. The
`analog output of the analog source 20 is coupled
`through the circuit conductor 22 to the input of a com-
`pressor 26. This device compresses the waveform am-
`plitude in a predetermined manner for providing a com-
`pressed analog signal at the output thereof. Due to the
`extremely large amplitude peak to average ratio en-
`countered in musical and voice type signals, a logarith—
`mic amplifier or compressor is especially appropriate
`for use in audio systems of this type. Using a logarithmic
`compressor, the wavefrom amplitude of the input signal
`will be logarithmically compressed to reduce the peak
`to peak waveform amplitude excursions which will be
`experienced during the course of the program material.
`Distortion induced upon the compressed analog signal
`by the action of the logarithmic amplifier may be re-
`duced by utilizing good circuit design techniques which
`may involve selecting time constants which compliment
`the type of program material to be transmitted.
`The compressed analog signal output of the compres-
`sor 26 is coupled by the circuit conductor 28 to the
`input of an analog to digital converter 30. Such analog
`to digital converters are well known in the art and usu-
`ally operate by generating an internal time base, sam-
`pling the analog signal input at some predetermined
`point in each of the time base segments, and then gener-
`ating a digital output responsive to the sampled level
`obtained during the sampling period. The output of the
`analog to digital converter 30 may be either parallel
`digital or serial digital. Various types of digital coding
`are common for such analog to digital converters. For
`example, the compressed analog signal may be con-
`verted to a digital signal of the type known as pulse
`amplitude modulation (PAM) in which the amplitude of
`the digital pulse represents the amplitude of the com-
`pressed analog signal during the sampling time period.
`In pulse duration modulation (PDM) the amplitude of
`
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`4,124,773
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`3
`the pulses remains constant, while the pulse width is
`varied to indicate the relative signal amplitude as mea-
`sured during the sampling period. The most common
`type of digital signal, and the type which may be pre-
`ferred in this system if sufficient bandwidth is available,
`is the pulse code modulation (PCM) in which the sam-
`pled amplitude is converted to a digitally coded signal,
`such as binary coded decimal (BCD). For example the
`binary coded PCM signals may be preferred because
`they are generally compatable with certain digital data
`transmission systems of the type used to transmit com-
`puter data, etc.
`The digital signal output of the analog to digital con-
`verter 30 is coupled through a circuit conductor 35 to
`one input of a digital interface device shown generally
`as 40. The digital interface device 40 comprises several
`subsystems including a digital storage subsystem 42 for
`receiving the digital signals and storing this information
`for later retrieval, and a digital processor and interroga—
`tor 50 which functions as an input/output device feed-
`ing the digital storage subsystem 42.
`An optional distortion reduction circuit includes a
`second analog—to-digital converter 55 which has a first
`input coupled by the circuit conductor 22 to the analog
`source 20 for forming a digital representation thereof.
`The output of the second analog-to-digital converter 55
`is coupled to a second input of the digital processor and
`interrogator 30 of the digital interface means 40 by the
`circuit conductor 91. Also,
`the digital processor 50
`further includes digital processing circuitry for mathe-
`matically operating on the uncompressed digital signal
`with an algorithm corresponding to the input-output
`function of the compressor 26 and then comparing the
`digital compressed representation of the input signal
`with the mathematically derived compressed digital
`input signal from the line 91, in order to derive an error
`or distortion signal. This signal is then used to operate
`upon the signal obtained from line 91 so as to remove
`those distortion products inherent in the compressor 26.
`This processed signal is then available for storage in the
`digital storage device 42.
`The digital interface device 40 includes a digital pro-
`cessor 50 for optimizing the format of the digital signals
`to interface with the format required by the storage
`system. The storage system 42 may include commonly
`available storage mediums such as magnetic tape, mag-
`netic discs, capacitance coded discs or other various
`types of mechanical recording mediums. Bandwidths of
`up to 5 MHz and recording times of up to 30 minutes for
`multiple channel tape recorders or disc recorders are
`common illustrations of the present state of the art for
`these devices. Digital data may be recorded at ex-
`tremely high bit rates with time division multiplexing
`being used to interleave the individual signals. On the
`other hand, frequency division multiplexing may be
`used to directly record on specific frequency band-
`widths the low bit rate signals representative of each of
`the digital signals.
`Electronic memories may also be used for the storage
`of these digital signals. Typical examples of electronic
`memories include bubble memories, Read Only Memo—
`ries (ROMS), Random Access Memory (RAMS) and
`Charge Coupled Devices (CCDs). The advances in
`these technologies, as well as other technologies now
`under development,
`indicate that
`inexpensive, high
`density, electronic memories will soon be available for
`providing relatively rapid access to large quantities of
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`digital information which can be stored and erased in a
`relatively small physical volume.
`The digital output from the digital storage subsystem
`42 is coupled by the circuit conductor 49 to another
`input of a digital processor and interrogatcr 50. The
`digital interrogator is designed to provide rapid access
`to the digital information stored within the digital stor—
`age subsystem 42. Therefore, the digital interrogator 50
`must be compatible with the digital storage subsystem
`42. While rapid access times in the range of l to 2 sec«
`onds are desirable, it is more likely that cost, power and
`size considerations may determine a tradecff whereby
`access times of from 3 to 10 seconds may be equally
`suitable.
`The digital interrogator 50 also includes a data refor-
`mating subsystem 56 which is designed to programma-
`bly reformatthe digital signals retrieved by the digital
`interrogator 50 from the digital storage subsystem 42 in
`order that the signal quality may be optimized with
`regard to the electrical characteristics of a communica-
`tions circuit 59. Data reformatting subsystems 56 in ac-
`cordance with these requirements are typically known
`as modern. A typical data modems may be capable of
`reformatting and transmitting digital data at rates of 4.8
`kBps, 7.2 kBps. 916 kBps. l9.2 kBps and 56 kBps. Of
`course, the required bit rate will be determined by the
`bandwidth of the communications circuits available, the
`format of the digital signal, the allowable bit error rate
`and the required signal quality.
`The digital signal output from the data reformatting
`subsystem 56 of the digital interrogator 50 is coupled to
`a first end of the communications circuit 59. The term
`communications circuit is used generically to describe
`the commonly available two-way communications links
`such as direct distance dial
`telephone lines, private
`leased lines, digital microwave communications net»
`works, satellite communications networks, and wide-
`band coaxial communications systems. At .the present
`time, narrow band or wide band telephone lines are the
`most cost effective method of distributing digital data
`from one point to another. However, the rapid growth
`of technology may change this economic limitation
`shortly. For example, when two-way coaxial lines are
`commonly available into the home such as CATV sys-
`tems and two-way interactive computer terminal sys-
`tems, the unused bandwidth on the coaxial cables may
`prove to be extremely cost effective. One of the primary
`advantages of the digital transmission of data is that the
`quality and quantity of the signal available may easily be
`changed responsive to the addition of increased band-
`width, without the necessity of complete system rede-
`Sign.
`A digital to analog converter 60 is coupled to a sec-
`ond end of the communications circuit 59 at a remote
`receiving location. The digital to analog converter 60
`will receive the digital signals along the communica-
`tions circuits and reconvert the digital signal to its 10-
`tharithmic analog representation. In some applications
`it may be possible to design the system such that the
`fomiat of the digital signal will be directly compatible
`with the required digital format of the digital to analog
`converter 69 so that no digital interface circuitry is
`required. However, when sophisticated digital incoding
`schemes are utilized it may be necessary to provide an
`additional level of interface circuitry, shown generally
`as 70, coupled to the second end of the communications
`line. A receiver digital interface subsystem 70 includes a
`second digital storage subsystem 72 having an input
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`4,124,773
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`5
`coupled to a communications line 59 by a circuit con-
`ductor 79. A circuit conductor 77 couples the output of
`the second digital interface subsystem 74. Another input
`of the digital interface subsystem 74 is coupled directly
`to the communications line 59. The digital interface
`subsystem 74 may receive directly the digital signals
`from the communications line 59 for reformatting and
`redirecting the- digital signals in the proper format
`through a circuit conductor 78 coupled from the output
`thereof to another input of the digital to analog con-
`verter 6D.
`In this manner, the digital interface subsystem 74 may
`act as a modem for reformatting the digital signals so as
`to be compatible with the format required by the digital
`to analog converter 60. If an asynchronous modem is
`used as the digital interface subsystem 74, the second
`digital storage subsystem 72 may be utilized as a buffer
`storage device for accumulating the digital data signals
`prior to their processing by the digital interface subsys-
`tem 74. Also, the second digital storage subsystem 72
`may comprise large capacity storage devices similar to
`those described for the digital storage subsystem 42,
`thereby enabling the storage of digital program material
`at the remote user location. These digital programs may
`be retrieved by the digital interface subsystem 74 in a
`manner similar to the operation of the digital interroga-
`tor 50 as previously explained.
`After the compressed analog signal is recovered by
`the digital to analog converter 60 it is coupled through
`a circuit conductor 68 to an antilogarithmic input of an
`expander 80. The expander 80 operates in a manner
`complimentary to the compressor 26. In the preferred
`embodiment of the present invention the expander 80 is
`an anti-logarithmic amplifier for reconstructing the
`original analog waveform from the compressed analog
`signal serving as the input thereto. The analog signal is
`then coupled from an output thereof through a circuit
`conductor 87 to the input of an audio amplifier 88 which
`is used to drive a transducer 90 or other type of electri-
`cal load through the electrical conductor 89.
`Another optional distortion reduction system similar
`in design and function to the one used on the previously
`discussed recording and storage circuitry may also be
`provided. Another digital to analog converter 92 has an
`input thereof coupled to the digital interface subsystem
`74 for mathematically expanding the digital signal
`therefrom according to an algorithm representative of
`the input-output function of the expander 80. The math-
`ematically derived analog signal is then coupled from
`an output through the circuit conductor 93 to another
`input of the expander 80 for being compared with the
`analog signal therefrom. An error or distortion signal is
`then fed back to the expander 80 for removing the dis
`tortion from the output analog signal, which is fed to
`the audio amplifier 88 through the circuit conductor 87.
`A command signal generator 100 is coupled to the
`communications circuit 59. In the case where the com-
`munications circuit 50 comprises a typical 3 KHz band-
`width telephone line, the command signal generator 100
`may comprise the TOUCHTONE telephone connected
`to this line and used for‘normal voice communications.
`The digital interrogator 50 as well as the digital inter-
`face subsystem 74 both contain command circuitry for
`responding to the tone command signals generated by
`the telephone. In this manner, codes may be designated
`for selecting the desired digital signals from the digital
`storage subsystem 42 or the second digital storage sub-
`system 72 by the operation of the command signal gen-
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`erator 100. In the case of wide band communications
`lines 59, the command generator 100 may comprise a
`digital command formatting for generating an innerac—
`tive digital signal for actuating the digital interrogator
`50 or the digital interface subsystem 74. Of course, the
`TOUCHTONE type command system could also be
`used on the wide band communications lines.
`The operation of the audio storage and distribution
`system will now be illustrated with reference to the
`FIGURE. First, an analog program source is coupled to
`the compressor for compressing the waveform ampli-
`tude. This compressed analog signal is then converted
`to a digital signal by the analog digital converter 30. A
`plurality of the digital signals are then sequentially
`stored within the digital storage subsystem 42 located at
`the central control location. As a user located at a re-
`mote location desires to listen to a selected one of the
`programs, the operator actuates the command signal
`generator 100 with a code representing the selected one
`of the stored programs. A command signal is transmit-
`ted along the communications circuit 59 and interpreted
`by the digital interrogator 50. The digital interrogator
`50 then retrieves the selected one of the stored digital
`signals from the digital storage subsystem 42. The digi-
`tal signal is then reformatted by the data reformatter 56
`and transmitted along the communications circuit 59.
`Depending on the chosen data format for the digital
`signal, which is largely determined by the characteris-
`tics of the communications circuit 59, the digital signal
`may be received directly by the digital to analog con-
`verter 60 for conversion into the compressed analog
`signal which is then coupled to the expander 80 in order
`to be re-expanded to the original waveform amplitude.
`The analog signal output of the expander 80 is then
`coupled to the audio amplifier 88 for driving the trans-
`ducer or load 90. If the characteristics of the communi-
`cations circuit 59 require a special digital format for
`optimizing the quality of the signal received at the re-
`mote users end, the digital signal may be received by the
`digital interface subsystem 74 and reformatted in a digi-
`tal code acceptable to the digital to analog converter 60.
`This digital signal is then processed as previously de-
`scribed.
`The command signal generator 100 may also be uti—
`lized to select from a more limited library of program
`material stored in the second digital storage subsystem
`72. This digital program material is retrieved by the
`operation of the digital interface subsystem 74 and cou-
`pled directly to the digital to analog converter 60 with—
`out being transmitted along the communications circuit
`59. The second digital storage subsystem 72 may also be
`available as a buffer storage location to facilitate the
`proper operation of the digital interface subsystem 74
`when operating in a modem configuration.
`The preferred embodiment of the audio storage and
`distribution system has been described as an example of
`the invention as claimed. However, the present inven-
`tion should not be limited in its application to the details
`illustrated in the accompanying drawing and the specifi-
`cation, since this invention may be practiced or con-
`structed in a variety of different embodiments. Also, it
`must be understood that the terminology and descrip-
`tions employed herein are used solely for the purpose of
`describing the general operation of the preferred em-
`bodiment and therefore should not be construed as
`limitations on the operability of the invention.
`1 claim:
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`'7
`1. An audio communications system for transmitting
`analog signals over a communications circuit, said sys-
`tem comprising in combination:
`compressor means for receiving the analog signal at
`an input thereof and compressing the waveform 5
`amplitude of the analog signal in a predetermined
`manner for generating a compressed analog signal
`at an output thereof;
`analog to digital converter means, having an input
`coupled to said output of said compressor means,
`for converting said compressed analog signal to a
`digital signal at an output thereof;
`digital interface means, having a first input coupled to
`said output of said analog to digital converter
`means, for storing and selectively transmitting said
`digital signals to an output thereof coupled to the
`communications circuit,
`said digital
`interface
`means including digital storage means coupled to
`said input for receiving and storing said digital 20
`signals, and retrieval means for recovering a se-
`lected one of said digital signals from said digital
`storage means for coupling to said output thereof,
`whereby selected ones of said digital signals may be
`randomly retrieved from said digital
`storage 25
`means;
`digital to analog converter means, having an input
`coupled at a remote location to the communica-
`tions circuit, for reconverting said digital signal to
`said compressed analog signal at an output thereof; 30
`expander means, having an input coupled to said
`output of said digital to analog converter means,
`for expanding the waveform amplitude of said
`compressed analog signal in a predetermined man—
`ner for reconstructing the analog signal;
`means for transmitting a selector signal to said re-
`trieval means from said remote location over said
`communication circuit; and
`means for decoding said selector signal for designat-
`ing a selected digital signal to be retrieved.
`2. The audio communications system as described in
`claim 1 wherein said digital storage means comprises
`electronic memories from one of Read Only Memories
`(ROMS) and Random Access Memories (RAMs).
`3. The audio communications system as described in
`claim 2 further comprising in combination:
`selection means coupled to said retrieval means for
`instructing responsive to a first command signal at
`an input thereof said retrieval means as to the se- 50
`lected ones of said digital signals to be retrieved;
`and
`command means for generating said first command
`signal at an output thereof coupled to said input of
`said selection means by the communications cir- 55
`cuit.
`4. The audio communications system as described in
`claim 3 wherein first command signals are responsive to
`telephone station selection comparable signals.
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`5. The audio communications system as described in
`claim 3 wherein said retrieval means and said digital to
`analog converter means each further comprises modem
`means for reformatting said digital signals for transmis—
`sion over the communications circuit, whereby the
`format of said digital signals may be Optimized to suit
`the character of the communications circuits.
`6. The audio communications system as described in
`claim 5 wherein the communications circuit comprises a
`telephone line having a bandwidth less than 4kHz.
`7. The audio communications system as described in
`claim 3 further comprising in combination:
`second digital storage means for receiving and stor-
`ing said digital signals; and
`'
`second retrieval means for recovering selected ones
`of said digital signals from said second digital stor-
`age means,-With said second retrieval means includ-
`ing an output coupled to a second input of said
`digital to analog converter means at the remote
`location, whereby a local source of said digital
`signals may be coupled to said digital to said analog
`conversion means.
`8. The audio communications system as described in
`claim 7 wherein an input of said second digital storage
`means is coupled to said communications circuit for
`receiving and storing said digital signals therefrom.
`9. The audio communications system as described in
`claim 3 wherein said compressor means comprises a
`logarithmic amplifier and wherein said expander means
`comprises an anti—logarithmic amplifier, with said loga-
`rithmic amplifier and said anti-logarithmic amplifier
`having complementary input-output functions.
`10. The audio communications system as described in
`claim 1 further comprising:
`another analog to digital converter means for receiv-
`ing the analog signal at an input thereof and for
`converting said analog signal to a digital signal at
`an output thereof; and wherein
`said digital interface means further includes computa-
`tion means for performing mathematical computa-
`tions on said digital signal for mathematically simu-
`lating said compressed analog signal from said
`compressor means, and wherein said digital inter-
`face means further comprises error correcting
`means for comparing said simulated compressed
`analog signal with said digital signal from said
`analog to digital converter and for correcting said
`digital signal responsive to any differences therebe-
`tween.
`11. The system as described in claim 1 further com-
`prising:
`.
`means for reformatting said selected digital signal for
`optimum transmission characteristics along the
`communications circuit.
`12. The system as described in claim 11 further com—
`prising;
`means for un-reformatting said reformatted digital
`signal, thereby recovering said digital signal.
`*
`ill
`#3
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