Information signal processing companding

Claim 2

In apparatus for recording an information signal on a recording medium by a recording (17) 110 device, gain control means comprising: means for defining a first transmission path for compressing said information signal; means defining a second transmission path for transmitting said information signal with substantially unity gain; and means for supplying the information signal to said recording device by way of said first path when the level of said information signal is below a predetermined value and for supplying said 74 R GB 2 052 220 A 15 0 information signal to said recording device by way of said second path with substantially unity gain when the level of said information signal is above said predetermined value.

Claim 3

Gain control means according to claim 1 70 wherein said means defining the first transmission path includes variable gain amplifier means having a gain which varies in response to a control signal supplied thereto and which compresses said information signal as a function of said information signal, and control means response to the compressed information signal from said variable gain amplifier means for producing said control signal.

Claim 4

Gain control means according to claim 2 wherein said variable gain amplifier means compresses said information signal in a logarithmic manner.

Claim 5

Gain control means according to claim 2 wherein said control means includes level detecting means for detecting the level of said compressed information signal from said variable gain amplifier means and for producing a detected output signal in response thereto, and non-linear means for producing said control signal 90 in response to said detected output signal.

Claim 6

Gain control means according to claim 4 wherein said level detecting means includes means for logarithmically converting said compressed information signal from said variable 95 gain amplifier means, and amplifier means for producing said detected output signal in response to the logarithmically converted signal.

Claim 7

Gain control means according to claim 4 wherein said non-linear means has an input output level characteristic with a first linear gradient when the level of said detected output signal is less than second predetermined value corresponding to the first-mentioned predetermined value, and a second linear gradient 105 greater than said first gradient when the level of said detected output signal is greater than said second predetermined value.

Claim 8

Gain control means according to claim 6 wherein said non-linear means includes first and 110 second resistive elements forming a voltage divider for voltage dividing said detected output signal so as to produce said first linear gradient, and means for varying the resistance value of one of said resistive elements for changing the voltage 115 dividing ratio of said voltage divider so as to produce said second linear gradient.

Claim 9

Gain control means according to claim 7 wherein said means for varying the resistance 1 55 value includes a series circuit of a diode, means for reverse biasing said diode, and a third resistive element, and said series circuit is connected in parallel to said one resistive element.

Claim 10

Gain control means according to claim 2 wherein said means defining the first transmission path further includes limiter means for limiting said compressed information signal from said variable gain amplifier at two independent levels.

Claim 11

Gain control means according to claim 9 130 wherein said limiter means includes a diode limiter circuit having first and second diodes, each connected in parallel between the output of said ariable gain amplifier means and a reference potential, and each being arranged in opposing relation to the other.

Claim 12

Gain control means according to claim 10 wh erein said limiter means further includes a capacitive element connected between said reference potential and said first and second diodes for providing a second reference potential higher than said first mentioned reference potential for low frequency components of said information signal.

Claim 13

Gain control means according to claim 11 wherein said limiter means further includes a first resistive element connected between the output of said variable gain amplifier means and said first and second diodes and a series circuit of a capacitive element and a resistive element connected in parallel with said first resistive element so as to reduce the effective resistance between the output of said variable gain amplifier and said first and second diodes for high frequency components of said information signal.

Claim 14

Gain control means according to claim 9 wherein said limiter means includes at least one transistor having a collector-emitter path connected between the output of said variable gain amplifier means and a reference potential.

Claim 15

Gain control means according to claim 13 wherein said limiter means further includes another transistor connected between the output of said variable gain amplifer means and a reference potential, and a capacitive element connected between the output of said variable gain amplifier means said transistors for imparting a frequency dependency to said limiter means.

Claim 16

Gain control means according to claim 1 wherein said means defining the second transmission path includes a resistive element connected in parallel with said first transmission path.

Claim 17

Gain control means according to claim 15 further comprising amplifier means having an input supplied with the compressed information signal from said first transmission path and with said information signal with substantially unity gain from said second transmission path whereby said compressed information signal and said information signal with substantially unity gain are added at the input of said amplifier means.

Claim 18

Gain control means according to claim 16 further comprising preemphasis means connected to said first and second transmission paths for pre-emphasizing the high frequency components of said information signal.

Claim 19

Gain control means according to claim 17 further comprising means defining a third transmission path for de-emphasizing high level, high frequency components of the information signal whereby a substantially flat frequency characteristic is imparted by said apparatus to high level components of said information signal.

Claim 20

Gain control means according to claim 18 16 GB 2 052 220 A 16 wherein said means defining a third transmission path includes high pass filter means for transmitting only high frequency components of said information signal,.and means for subtracting said high frequency components of said information signal from the added signal produced by the addition of said compressed 60 information signal and said information signal with substantially unity gain for high levels of said information signal.

Claim 21

In apparatus for reproducing an information signal from an encoded information signal which has been recorded on a recording medium with the information signal effectively compressed for levels thereof below a predetermined value and with the information signal effectively transmitted with substantially unity gain for levels thereof above said predetermined value; gain control means for reproducing said information signal from said encoded information signal, the gain control means comprising; means defining a first transmission path for expanding said encoded information signal into an expanded signal; and means defining a second transmission path for negatively feeding back said expanded signal to said first transmission path with substantially unity gain.

Claim 22

In apparatus for reproducing an information signal from an encoded information signal which has been recorded on a recording medium with the information signal effectively compressed for levels thereof below a predetermined value and with the information signal effectively transmitted with substantially unity gain for levels thereof above said predetermined value; gain control means for reproducing said information signal from said encoded information signal, the gain control means comprising; means defining a first transmission path for expanding said encoded information signal into an expanded signal; and means defining a second transmission path for negatively feeding back said expanded signal to said first transmission path with substantially unity gain.

Claim 23

Gain control means according to claim 20 wherein said means defining a first transmission path includes variable gain amplifier means 85 having a gain which varies in response to a control signal supplied thereto and which produces said expanded signal as a function of said encoded information signal, and control means responsive to said encoded information signal for producing said control signal.

Claim 24

Gain control means according to claim 21 wherein said variable gain amplifier means expands said encoded information signal in a logarithmic manner.

Claim 25

Gain control means according to claim 21 wherein said control means includes level detecting means for detecting the level of said encoded information signal and for producing a detected output signal in response thereto, nonlinear means for producing an output signal in response to said detected output signal, and inverting means for producing said control signal in response to said output signal from said nonlinear means.

Claim 26

Gain control means according to claim 23 wherein said non-linear means has an input- output level characteristic with a first linear gradient when the level of said detected output signal is less than a second predetermined value corresponding to the first-mentioned predetermined value, and with a second linear gradient when the level of said detected output signal is greater than said second predetermined value.

Claim 27

Gain control means according to claim 21 wherein said means defining a first transmission path further includes limiter means for coring said encoded information signal.

Claim 28

Gain control means according to claim 25 further comprising an input terminal; and wherein said limiter means includes first and second diodes connected in parallel and opposing relation between said input terminal and said variable gain amplifier means.

Claim 29

Gain control means according to claim 26 wherein said limiter means includes additional amplifier means having input and output terminals, said first and second diodes are connected in parallel between said input and output terminals of said amplifier means, a capacitive element connects said in put terminal of, the additional amplifier means to a reference potential, and a series circuit of a resistive element and another capacitive element is connected in parallel with another resistive element between the output terminal of said additional amplifier means and said first and second diodes for imparting a frequency characteristic to said limiter means.

Claim 30

Gain control means according to claim 20 wherein said means defining the second transmission path includes a feedback resistor for negatively feeding back said expanded signal to said first transmission path.

Claim 31

Gain control means according to claim 20 further comprising a deemphasis circuit connected to said first and second transmission paths for de-emphasizing the high frequency components of said encoded information signal.

Claim 32

Gain control means according to claim 29 further comprising a third transmission path for positively feeding back the high frequency components of said expanded signal to said first transmission path.

Claim 33

Gain control means according to claim 1 and substantially as any one of the variants hereinbefore described with reference to the accompanying drawings. Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained. :1 1