EP0693202A4 - - Google Patents

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Publication number
EP0693202A4
EP0693202A4 EP94914041A EP94914041A EP0693202A4 EP 0693202 A4 EP0693202 A4 EP 0693202A4 EP 94914041 A EP94914041 A EP 94914041A EP 94914041 A EP94914041 A EP 94914041A EP 0693202 A4 EP0693202 A4 EP 0693202A4
Authority
EP
European Patent Office
Prior art keywords
signal
magnetic medium
noise
medium
remanent noise
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP94914041A
Other languages
English (en)
Other versions
EP0693202A1 (fr
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/046,071 external-priority patent/US5587654A/en
Priority claimed from US08/046,040 external-priority patent/US5365586A/en
Application filed filed Critical
Publication of EP0693202A1 publication Critical patent/EP0693202A1/fr
Publication of EP0693202A4 publication Critical patent/EP0693202A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07F—COIN-FREED OR LIKE APPARATUS
    • G07F7/00—Mechanisms actuated by objects other than coins to free or to actuate vending, hiring, coin or paper currency dispensing or refunding apparatus
    • G07F7/08—Mechanisms actuated by objects other than coins to free or to actuate vending, hiring, coin or paper currency dispensing or refunding apparatus by coded identity card or credit card or other personal identification means
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
    • G06F21/10—Protecting distributed programs or content, e.g. vending or licensing of copyrighted material ; Digital rights management [DRM]
    • G06F21/101—Protecting distributed programs or content, e.g. vending or licensing of copyrighted material ; Digital rights management [DRM] by binding digital rights to specific entities
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
    • G06F21/70—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer
    • G06F21/78—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure storage of data
    • G06F21/79—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure storage of data in semiconductor storage media, e.g. directly-addressable memories
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K1/00—Methods or arrangements for marking the record carrier in digital fashion
    • G06K1/12—Methods or arrangements for marking the record carrier in digital fashion otherwise than by punching
    • G06K1/125—Methods or arrangements for marking the record carrier in digital fashion otherwise than by punching by magnetic means
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/08—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means
    • G06K19/10—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means at least one kind of marking being used for authentication, e.g. of credit or identity cards
    • G06K19/12—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means at least one kind of marking being used for authentication, e.g. of credit or identity cards the marking being sensed by magnetic means
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/01—Details
    • G06K7/015—Aligning or centering of the sensing device with respect to the record carrier
    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07F—COIN-FREED OR LIKE APPARATUS
    • G07F7/00—Mechanisms actuated by objects other than coins to free or to actuate vending, hiring, coin or paper currency dispensing or refunding apparatus
    • G07F7/08—Mechanisms actuated by objects other than coins to free or to actuate vending, hiring, coin or paper currency dispensing or refunding apparatus by coded identity card or credit card or other personal identification means
    • G07F7/086—Mechanisms actuated by objects other than coins to free or to actuate vending, hiring, coin or paper currency dispensing or refunding apparatus by coded identity card or credit card or other personal identification means by passive credit-cards adapted therefor, e.g. constructive particularities to avoid counterfeiting, e.g. by inclusion of a physical or chemical security-layer
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00094—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00094—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers
    • G11B20/00123—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers the record carrier being identified by recognising some of its unique characteristics, e.g. a unique defect pattern serving as a physical signature of the record carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
    • G11B20/1816—Testing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/24—Signal processing not specific to the method of recording or reproducing; Circuits therefor for reducing noise
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B21/00—Head arrangements not specific to the method of recording or reproducing
    • G11B21/02—Driving or moving of heads
    • G11B21/10—Track finding or aligning by moving the head ; Provisions for maintaining alignment of the head relative to the track during transducing operation, i.e. track following
    • G11B21/106—Track finding or aligning by moving the head ; Provisions for maintaining alignment of the head relative to the track during transducing operation, i.e. track following on disks
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G11B5/027—Analogue recording
    • G11B5/035—Equalising
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/54—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head into or out of its operative position or across tracks
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B5/596—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks
    • G11B5/59605—Circuits
    • G11B5/59611—Detection or processing of peak/envelop signals
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B5/596—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks
    • G11B5/59633—Servo formatting
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2211/00—Indexing scheme relating to details of data-processing equipment not covered by groups G06F3/00 - G06F13/00
    • G06F2211/007—Encryption, En-/decode, En-/decipher, En-/decypher, Scramble, (De-)compress
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B33/00—Constructional parts, details or accessories not provided for in the other groups of this subclass
    • G11B33/10—Indicating arrangements; Warning arrangements
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/488—Disposition of heads

Definitions

  • a magnetic medium may be DC saturated and its output then measured to determine its remanent state or remanent noise.
  • the inventors have confirmed that this remanent noise is a function of the magnetic microstructure by comparing the remanent noise after a positive DC saturation with the remanent noise after a negative DC saturation. It has been found that these wave forms are virtual "mirror images" of each other thereby demonstrating a close correlation. Simi ⁇ larly, other methodologies were used to confirm that the remanent noise was determinative, repeatable, and related to the physical microstructure of the magnetic medium itself. Remanent noise arising from the permanent micro ⁇ structure exhibits identifiable features characteristic of that permanent microstructure after practically any magnetic history. See Spatial Noise Phenomena of Longi ⁇ tudinal Magnetic Recording Media by Hoinville, Indeck and Muller, IEEE Transactions on Magnetics. Volume 28, No. 6, November 1992, the disclosure of which is incorporated herein by reference.
  • the inventive technique disclosed and claimed herein relies upon the discovery that the microscopic structure of the magnetic medium itself is a permanent random arrangement of microfeatures and therefore deter- ministic.
  • the recording medium's physical microstructure remains fixed for all conventional recording processes.
  • the position and orientation of each particle does not change within the binder for any application of magnetic field; in thin film media, the microcrystalline orienta ⁇ tions and grain boundaries of the film remain stationary during the record and reproduce processes. It is the magnetization within each of these fixed microfeatures that can be rotated or modified which forms the basis of the magnetic recording process.
  • a region of a magnet ⁇ ic medium is saturated in one direction by a large ap ⁇ plied field, the remanent magnetization depends strongly on the micro-structure of the medium. This remanent state is deterministic for any point on the recording surface.
  • Each particle or grain in the medium is hun ⁇ dreds to thousands of Angstroms in dimension. Due to their small size, a small region of the magnetic surface will contain a very large number of these physical enti- ties. While the fabrication process normally includes efforts to align these particles, there is always some dispersion of individual orientations. The actual devia ⁇ tions will be unique to a region of the medium's surface making this orientation deterministic and making its effects susceptible to elimination.
  • noise reduction enables increase in storage capacity, increase in data rates, and eases the burden on transducers, medium, and system design and fabrication.
  • this discovery has been made by the inventors herein, noise reduction techniques based on this discovery have not been implemented.
  • this noise component of remanent noise is deterministic, it may be reliably repeated and measured at any particular point on a magnetic medium. Accordingly, the inventors have de ⁇ veloped several techniques which take advantage of this fact for producing uncorrupted pre-recorded signals which may be played back by any playback device but which, when played back, have already been compensated for the rema ⁇ nent noise component.
  • a magnetic record- ing may be recorded at the factory with a signal which has been first compensated for remanent noise such that as the signal is played back later the playback signal or read signal has the remanent noise component virtually eliminated.
  • the remanent noise component may very well be the most significant factor in noise emanating from pre-recorded magnetic media, this noise reduction technique may very well provide a dramatic reduction in noise with no required modification to the tremendous number of playback machines presently in the public's hands. This would include playback machines for the entertainment industry, etc.
  • the remanent noise is first determined and the recording device compensates the original signal for the remanent noise before writing the compensated signal on the magnetic medium.
  • a second methodology will also create uncorrupted pre-recorded signals on magnetic medium.
  • the signal is first written on the magnetic medium, the written signal is then read from the magnetic medium, this read signal is then compared with the original sig- nal. The differences therebetween are determined to be noise, the greatest component of which is deterministic medium noise.
  • the original signal is compensated to eliminate this noise before being recorded back at the same location on the magnetic medium.
  • any other readback or playback machine would then produce a signal which has been compensated for remanent noise.
  • the inventors have developed a methodology for compensating a signal read from a magnetic medium for remanent noise in real time.
  • This methodology permits a playback device to be manufactured and sold which can play back pre-recorded magnetic medium which has not itself been compensated prior to recording, and produce a signal which is compensated on readback.
  • the signal is first read from the magnetic medium, the remanent noise is determined for said magnetic medi ⁇ um, such as by saturating the magnetic medium and reading the remanent noise directly therefrom, and the signals are then compared to eliminate the noise from the origi ⁇ nal corrupted signal prior to use.
  • a playback device may take a pre-recorded magnetic medium whose signal has not been compensated, and transform it into a magnetic medium with a compensated signal recorded there- on such that further playbacks of the same magnetic medi ⁇ um would possibly not require compensation.
  • a user with a suitable playback machine may very well transform his entire collection of recorded media from non-compensated to compensated magnetic media.
  • the present invention is elegantly simple and adapted for implementation by conventional re- cording transducers as are commonly found and used in virtually every read or read/write device presently uti ⁇ lized by the public at large.
  • Such examples include cassette players, magneto-optic disc players, and VCRs.
  • a conventional recording transducer need merely DC saturate a specified portion of a magnetic medium, and then "read” or “play back” the remanent noise which remains. This remanent noise, which is an analog signal, may then be used to compensate an original signal, such as a musical program, dramatic reading, etc.
  • Figure 1 is a magnified representative depiction of the microscopic structure of a region of magnetic medium
  • Figure 2 is a magnified depiction of several tracks of a magnetic medium having microscopic structure representatively shown thereon;
  • Figure 3 depicts three conventional recording transducers and a magnetic medium traveling thereunder;
  • Figure 4 is a perspective view of a magneto-optic disc player with a magneto-optic disc in its tray;
  • Figure 5 is a cassette player depicting a cassette tape for play therein;
  • Figure 6 is a perspective view of a VCR with a tape ready for insertion
  • Figure 7 is a schematic diagram of the write-read- write embodiment of the invention.
  • FIG. 8 is a block diagram of the electronics shown in Figure 7. Detailed Description of the Preferred Embodiment
  • a region of magnetic medium 20 is built up with a plurality of macrocrystalline structures 22 in a random pattern.
  • This microcrystalline structure 22 is comprised of particles or grains varying from hundreds to thousands of Angstroms in diameter.
  • the view of Figure 1 is greatly enlarged and magnified in order to depict this physical phenomena.
  • this microcrystalline structure extends throughout the magnetic medium even though the magnetic medium 24 shown in Figure 2 may be itself comprised of tracks 26, 28, 30 as well known in the art.
  • FIG. 3 a plurality of conven ⁇ tional recording transducers 32, 34, 36 are shown mounted in a transducer transport 37 with a traveling magnetic medium 38 controllably driven past recording transducers 32, 34, 36 all as is well known in the art.
  • Recording transducers 32-36 are all connected to electronic cir ⁇ cuitry 40, as well known in the art, to control and read their input and output and further process signals for playback or other use.
  • FIG 3 Although only three transducers 32, 34, 36 are being shown in Figure 3, it will be well understood to those of ordinary skill in the art that a plurality of recording transducers of any number may just as easily be provided and, as taught herein, may be re- quired in order to effect the purposes of the present invention.
  • the recording transducers 32-36 as shown in Figure 3 may be considered as part of a device which is used to create pre-recorded magnetic medium with remanent noise compen- sated recordings.
  • the device shown in Fig ⁇ ure 3 may be considered as a playback unit of either a specialized playback device with means for creating a remanent noise compensated signal from a non-compensated pre-recorded signal, or a standard playback device which may be used to play back a remanent noise compensated magnetic medium. All of these functions are achieved with conventional recording transducers and therefore are readily implemented using existing and available technol ⁇ ogy.
  • a remanent noise compensated signal may be pre- recorded onto a magnetic medium by utilizing the follow ⁇ ing method.
  • the remanent noise of the magnetic medium may first be determined by DC saturating the medium and then reading the remanent noise with a conventional re ⁇ cording transducer. This would take transducer 32 to saturate the medium and transducer 34 to read the rema ⁇ nent noise.
  • the original signal would then be compensat ⁇ ed, using conventional compensation circuits as is well known in the art to modify the original signal such that it may then be recorded by recording transducer 36. In this manner, using this method and device as shown in Figure 3, a pre-compensated recording, pre-compensated for remanent noise, may be created on magnetic medium 38.
  • the remanent noise is itself capable of being used for indexing the transducers 32-36 to thereby ensure that the compensated signal is recorded by trans ⁇ ducer 36 for the remanent noise which in fact appears at that point on the magnetic medium for which said compen ⁇ sation has been made.
  • the remanent noise is random, it is unique to any particular point on the magnetic medium and thus can be used to identify such point for benchmark purposes. While this is the perferred embodiment, it should be understood that the remanent noise is always there, whether the medium has been recorded over or not. Therefore, it is not strictly necessary that the speci- fied portion of medium containing the remanent noise be DC saturated, or DC saturated in the same polarity in order to obtain the remanent noise.
  • Still another methodology may be used to create a pre ⁇ recorded magnetic medium having a signal recorded thereon which is remanent noise compensated.
  • This second embodi ⁇ ment involves the steps of first writing the original signal on the magnetic medium, such as for example by transducer 32 in Figure 3, reading the recorded signal from said magnetic medium such as by transducer 34, com ⁇ paring the read signal with the original signal to deter ⁇ mine the differences therebetween, compensating the orig ⁇ inal signal, and then writing the compensated signal with transducer 36.
  • magnetic medium 38 would thus receive a recorded signal which has been com ⁇ pensated for the remanent noise inherent in the magnetic medium 38.
  • this generalized model compensates for additive medium noise and explains a design approach for implementing this embodiment with a silicon tap delay line.
  • the signal s- ⁇ t) is processed by a write head, repre ⁇ sented by h(t) onto a magnetic medium.
  • the signal is corrupted by two kinds of medium noise, non-repeatable medium noise n x (t) and repeatable additive medium noise n d (t).
  • This corrupted signal is then read by a read head which processes it as represented by a func ⁇ tion g(t).
  • the signal s- ⁇ is processed as represented by a function b(t) which is the equivalent of a write and read function, and then subtracted from the output of the read head. Additionally, an electronics noise signal w x (t) is added to represent the electronics noise. The result is an error function e(t) which is representative of the total noise introduced in the sig ⁇ nal s- ⁇ t) by a write and read function. Next, the error function e(t) is then processed by a filter function c(t) which is the inverse of the noise expected to be added by a later write and read function.
  • the output of the filter function c(t) is subtracted from the data signal (t) and a write head processes this signal with the function h(t) to record it onto a magnetic medium where it again suffers corruption through the two kinds of magnetic medium noise, repeatable additive medium noise n d (t) and also non-repeatable medium noise n 2 (t).
  • a signal desired to be re ⁇ corded, s(t) has been recorded in a precompensated manner as the function c(t) subtracts out the effects of the write function, a later expected read function and the expectedjcrepeatable additive medium noise n d (t).
  • a signal output y(t) is produced which is clearly compensated for.
  • FIGs 7 and 8 Further explanation of this write-read-write embodiment of the present invention is found in Figures 7 and 8.
  • a first write head 102 writes the signal s x (t) on the medium 104.
  • the recorded signal is then read by read head 106 which produces an output y- ⁇ t) to an electronics circuit 108, as explained in Figure 8.
  • the electronics 108 produces a compensated data signal which is then written by write head 110 back on the magnetic medium 104.
  • the write head 110 thus writes a precompensated version of the data signal s(t) which, after being read by another read head (not shown) produces an output of data signal s(t) which has been compensated for additive repeatable magnetic noise.
  • the electronics 108 includes an adder 112 which subtracts an output signal d(t) from ideal channel 114 having a function b(t) which processes the diagnostic signal s x (t) as equivalent to a write and read function.
  • Diagnostic signal generator 115 processes the data signal s(t) to produce the diagnostic signal s- ⁇ t).
  • s.(t) could be a DC saturation sig ⁇ nal.
  • the output of adder 112 produces an error signal e(t) which is then compensated by compensation filter 116 through a signal transformation function c(t).
  • the compensation filter function c(t) is the inverse of the noise expected to be added by a write and read function.
  • a second adder 118 subtracts the output of compensation filter 116 from the data signal s(t) to produce a signal which corresponds to a pre- compensated data signal for writing onto the magnetic medium by write head 110.
  • the general ⁇ ized model and algorithm for each of the functions in ⁇ cluded in Figures 7 and 8 may be readily determined by one of ordinary skill in the art from the equations given in Exhibit A.
  • a playback device may be manufactured and sold which is capable of producing a noise compensated signal from recordings on magnetic media which have not been noise compensated.
  • the signal is first read, such as by recording transducer 32 in Figure 3, the remanent noise is then determined such as by saturating the magnetic medium with a signal from transducer 34 and reading the remanent noise with transducer 36, and then the original signal would be compensated with said remanent noise prior to playback or other processing.
  • a fourth transducer may be provided to re-record either the original signal or the compensated signal back on the magnetic medium 38 for subsequent playback.
  • conventional recordings on mag ⁇ netic media may be compensated for remanent noise prior to playback.
  • magnetic media may be transformed from uncompensated to noise compensated recordings.
  • a device may be made and sold for use with the vast in ⁇ ventory of pre-recorded magnetic media presently in the public's hands.
  • the unique remanent noise pattern may be used as a benchmark to locate a transducer at a particular position in a magnetic medium.
  • the conven ⁇ tional recording transducers 32-36 as shown in Figure 3 could be readily used to determine the remanent noise at a particular position on the magnetic medium 38. This could then be used to reposition the transducers 32-36 at the start or finish of an edit, or otherwise to precisely position a conventional recording transducer with respect to the magnetic medium.
  • This application would provide significant advantages in dubbing, etc. which is commonly used for taking rough cuts of many kinds of programs and editing them for final production.
  • a magneto-optic disc player 64 has a magneto-optic disc 66 in its tray 68 ready for play. As explained herein, a magneto-optic disc player 64 may play back remanen- noise compensated magneto-optic discs 66. Furthermore, although not presently commer ⁇ cially available for home use, magneto-optic disc players 64 may soon be available which are capable of recording onto magneto-optic discs 66.
  • magneto-optic discs 66 may be noise compensated when played back, even though its original signal was not recorded in a noise compensated format, and CD player 64 used to re-record a noise compensated signal back onto magneto-optic disc 66.
  • a cassette player 72 as shown in Figure 5 has a cassette 70 being inserted therein for play.
  • This magnetic medium is also susceptible to implementa ⁇ tion of the inventors' methodologies to enhance the re ⁇ cord and/or playback of cassette 70 in remanent noise compensated format.
  • FIG. 6 A last example of an implementation of the in- ventors' methodologies is shown in Figure 6 and includes a VCR 74 with a video tape cassette 76 being inserted therein.
  • the video tape cassette 76 is a magnetic medium, it is also susceptible to the noise compensation methodologies disclosed and claimed herein.
  • Much of the noise in magnetic recording systems is due to intrinsic properties of the magnetic medium itself. Much of this noise is repeatable in that identical waveforms recorded in the same place on the medium (with an erasure in between) have highly corre ⁇ lated noise. This effect is exploited in the present paper through the design of systems to estimate and subsequently correct the distortion of the recorded waveform due to medium noise.
  • the approach may be applicable to other storage channels whose noise is medium dependent such as magneto-optic media.
  • a method for optimally reducing repeatable addi ⁇ tive medium noise is proposed. Simulations of this system have been run and the results are promising.
  • the channel is the magnetic medium.
  • the medium may corrupt the signal, and if modeled as additive noise, average statistics of this medium noise may be estimated and used in system design to improve the performance of the system.
  • Other sources of noise include receiver noise and head noise, Even when these latter two noise sources are considered, the medium noise limits the system performance.
  • the authors have developed models for magnetic media [1,2] as have others (3,4,5,6,7]. These models account for the fact that medium noise arises from the microscopic properties of the record ⁇ ing medium. These properties are deterministic once the medium is manufactured.
  • the proposed strategy is to make on-line measurements of the medium noise and then to use these measurements in signal design. Possible ways to accomplish this strategy are discussed below. They may be classified as "write-read-write" recording strategies. First a diagnostic signal is written on the medium, second the resulting magnetization pattern is read, and third an information carrying signal is recorded. The design of the second written signal depends on the model for the medium noise.
  • FIG. 1 Traditional model for a magnetic recording system. This figure is from the Introduction to the Special Issue on Coding for Storage Devices, IEEE Transactions on Information Theory, vol. 37, Hay 1991, p. 709.
  • FIG. 2 Shown in Figures 2 is a block diagram description of the write-read-write recording pro ⁇ cess.
  • Figure 2 shows three heads flying over a magnetic medium. The first records a diag ⁇ nostic signal S ⁇ jt). The second reads the resulting magnetization on the medium. Third, a signal that has been computed by the electronics and includes the desired signal and compen ⁇ sation for the medium noise is written onto the medium. When the information is read at a later time, the signal-to-noise ratio will be significantly higher, resulting in better recovery of the desired signal.
  • the crucial design of the electronics block is based on a model for the manner in which the medium noise is manifested. The discussion in this paper is based on an additive model for the medium noise.
  • Shown in Figure 3 is an approximate linear model of a magnetic recording system.
  • all blocks are assumed to be linear and time-invariant, all random processes are assumed to be wide-sense stationary.
  • a diagnostic signal . (0 is written using the write head (J ⁇ (t)), medium noise is added (n d (t) + n ⁇ (t)), the signal is read (g( ) introducing electronics noise w ⁇ t)).
  • Kt) - (g * ⁇ )(t) (where * denotes convolution).
  • the error signal e(t) yj(t) - (jb * S ⁇ )(r) equals the part of the received voltage wave ⁇ form due to system noise.
  • the noise has a repeatable component, n d (t), due to the medium, and two unrepeatable components, nj(/) due to the medium, and W ⁇ (t) due to the electronics.
  • the goal is to compensate for the repeatable component To do this, c(t) is filtered, sub ⁇ tracted from 5(t), the information-bearing signal to be recorded, then recorded with the write head again.
  • Figure 3 Approximate linear model Tor the magnetic recording channel.
  • This model includes wide sense stationary additive Gaussian noise components. There are two input signals sl(t), a diagnostic signal, and s(t), an information bearing signal. The repeatable medium noise is nd(t).
  • the design problem may be stated as minimizing the distortion in the waveform y(t) that is eventually read due to the repeatable component of medium noise.
  • c(t) may be designed from the reduced system shown in Figure 4. In that figure, the information-bearing signal j(t) and the diagnostic signal S ⁇ t) have been removed. Let the distortion be measured in terms of noise power, Then the goal is to design c(t) to ⁇ iinimize the signal power in y e (t), the noise component of the output, For any real system design, there will be a constraint class, C, for the c(t) so thai they are realizable.
  • the unconstrained solution to (3) if it exists is where P(_ ⁇ ) and Q( ⁇ ) zie the Fourier transforms of p(t) and q(t), respectively, and the sub ⁇ script u in c u (t) represents the fact that this is an unconstrained optimum solution. This may not exist because Q ⁇ ) may have zeros. Also, even if this solution exists, it may not be real ⁇ istically realizable. Usually some type of constraint is added so that the solution for c(t) exists and is well-behaved (easily realizable). In the following section, the constraint of the solution being implementable by a tapped delay line (and thus easily realizable using stan ⁇ dard VLSI design) is added.
  • the limiting increase in capacity is determined by the change in the power spec ⁇ trum of the channel.
  • the constraint class is the set of c(t) such that
  • equation (10) may be rewritten compactly as
  • the step response of the read head is given by
  • TS/2 is the half width of the Lorentz pulse. Differentiating this with respect to t we get the impulse response function g(t) of the read head
  • Figure 5 compares the noise powers before and after signal precompensation obtained in 1000 runs.
  • Figures 6 and 7 show typical read waveforms obtained by writing the signal without and with compensation.

Abstract

Procédé et appareil permettant de déterminer le bruit résiduel d'un support magnétique (104) grâce à la saturation (102) par courant continu d'une région dudit support et à la mesure (106) de la magnétisation par courant continu restante. Des transducteurs d'enregistrement classiques peuvent être utilisés pour déterminer le bruit résiduel. Après détermination, le bruit résiduel peut alors être compensé soit en mode de lecture, soit en mode d'enregistrement (110), soit dans les deux modes pour tous les types de supports magnétiques, y compris les bandes vidéo, les bandes sonores, etc.
EP94914041A 1993-04-09 1994-04-05 Procede et appareil de reduction du bruit dans des supports magnetiques Withdrawn EP0693202A1 (fr)

Applications Claiming Priority (7)

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US08/046,071 US5587654A (en) 1993-04-09 1993-04-09 Method and apparatus for noise reduction in magnetic media recordings
US46040 1993-04-09
US08/046,040 US5365586A (en) 1993-04-09 1993-04-09 Method and apparatus for fingerprinting magnetic media
US20899794A 1994-03-10 1994-03-10
PCT/US1994/003722 WO1994024639A1 (fr) 1993-04-09 1994-04-05 Procede et appareil de reduction du bruit dans des supports magnetiques
US46071 2002-01-11
US208997 2002-07-31

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WO1994024641A1 (fr) * 1993-04-09 1994-10-27 Washington University Procede et appareil de commande de processus, de regulation de tension et de test de supports d'informations magnetiques

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JPS59127209A (ja) * 1983-01-08 1984-07-23 Oki Electric Ind Co Ltd 磁気媒体読出し時の外来ノイズ除去方法
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