Compressors, expanders and noise reduction systems

Claim 2

A signal compressor, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, and a further path having an input connected to the input terminal and an output connected to the combining means for combining with the main signal component, so as to buck the level of the main signal component, a further signal component, the further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 3

A signal compressor according to claim 1, comprising a filter in parallel with said circuit means, said circuit means being connected directly to elements of the filter so that the impedance of said circuit means influences the characteristics of the filter and at least one stop band of the filter narrows as the level of the signal at the input to the further path rises and said impedance falls.

Claim 4

A signal expander, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, and a further path having an input connected to the output terminal and an output connected to the combining means for combining with the main signal component, so as to boost the level of the main signal component, a further signal component, the further path including circuit means having the characteristics of a conVeyor such that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 5

A signal expander, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, and a further path having an input connected to the output terminal and an output connected to the combining means for combining with the main signal component, so as to boost the level of the main signal component, a further signal component, the further path including circuit means having the characteristics of a conVeyor such that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 6

A signal expander according to claim 3, comprising a filter in parallel with said circuit means, said circuit means being connected directly to elements of the filter so that the impedance of said circuit means influences the characteristics of the filter and at least one stop band of the filter narrows as the level of the signal at the input to the further path rises and said impedance falls.

Claim 7

A signal compressor, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, and a further path having an input connected to the output terminal and an output connected to the combining means for combining with the main signal component, so as to boost the level of the main signal component, a further signal component, the further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 8

A signal compressor, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, and a further path having an input connected to the output terminal and an output connected to the combining means for combining with the main signal component, so as to boost the level of the main signal component, a further signal component, the further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 9

A signal compressor according to claim 5, comprising a filter in parallel with said circuit means, said circuit means being connected directly to elements of the filter so that the impedance of said circuit means influences the characteristics of the filter and at least one stop band of the filter narrows as the level of the signal at the input to the further path rises and said impedance falls.

Claim 10

A noise reduction system comprising a signal compressor having an input terminal and an output terminal, a signal expander having an input terminal and an output terminal, and an information channel for transferring a signal from the compressor output terminal to the expander input terminal, each of the compressor and expander comprising a main signal path including a combining means and extending from the respective input terminal to the respective output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, the compressor further comprising a further path having an input connected to the compressor input terminal and an output connected to the combining means of the compressor for combining with the main signal component, so as to buck the level of the main signal component in the compressor, a further signal component, the expander further comprising a further path having an input connected to the expander output terminal and an output connected to the combining means of the expander for combining with the main signal component, so as to boost the level of the main signal component in the expander, a further signal component, each further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the respective further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 11

A noise reduction system comprising a signal compressor having an input terminal and an output terminal, a signal expander having an input terminal and an output terminal, and an information channel for transferring a signal from the compressor output terminal to the expander input terminal, each of the compressor and expander comprising a main signal path including a combining means and extending from the respective input terminal to the respective output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, the compressor further comprising a further path having an input connected to the compressor input terminal and an output connected to the combining means of the compressor for combining with the main signal component, so as to buck the level of the main signal component in the compressor, a further signal component, the expander further comprising a further path having an input connected to the expander output terminal and an output connected to the combining means of the expander for combining with the main signal component, so as to boost the level of the main signal component in the expander, a further signal component, each further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the respective further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 12

A noise reduction system comprising a signal compressor having an input terminal and an output terminal, a signal expander haVing an input terminal and an output terminal, and an information channel for transferring a signal from the compressor output terminal to the expander input terminal, each of the compressor and expander comprising a main signal path including a combining means and extending from the respective input terminal to the respective output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, the compressor further comprising a further path having an input connected to the compressor output terminal and an output connected to the combining means of the compressor for combining with the main signal component, so as to buck the level of the main signal component in the compressor, a further signal component, the expander further comprising a further path having an input connected to the expander input terminal and an output connected to the combining means of the expander for combining with the main signal component, so as to boost the level of the main signal component in the expander, a further signal component, each further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the respective further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 13

A noise reduction system comprising a signal compressor having an input terminal and an output terminal, a signal expander haVing an input terminal and an output terminal, and an information channel for transferring a signal from the compressor output terminal to the expander input terminal, each of the compressor and expander comprising a main signal path including a combining means and extending from the respective input terminal to the respective output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, the compressor further comprising a further path having an input connected to the compressor output terminal and an output connected to the combining means of the compressor for combining with the main signal component, so as to buck the level of the main signal component in the compressor, a further signal component, the expander further comprising a further path having an input connected to the expander input terminal and an output connected to the combining means of the expander for combining with the main signal component, so as to boost the level of the main signal component in the expander, a further signal component, each further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the respective further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 14

A circuit switchable between the configurations of a signal compressor and a signal expander, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, a further path having an input and an output for providing a further signal component at said output, and switching means having a compressor setting and an expander setting, the switching means establishing in the compressor setting a first loop from a point in the main path, through the further path, to the combining means such that the further signal component bucks the main signal component, and the switching means establishing in the expander setting a second loop from a point in the main path, through the further path, to the combining means such that the further signal component boosts the main signal component, the point in the main path to which the input of the further path is connected being on opposite sides of the point in the main path at which the further signal component is combined with the main signal component in the compressor and expander settings respectively, the further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 15

A circuit switchable between the configurations of a signal compressor and a signal expander, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, a further path having an input and an output for providing a further signal component at said output, and switching means having a compressor setting and an expander setting, the switching means establishing in the compressor setting a first loop from a point in the main path, through the further path, to the combining means such that the further signal component bucks the main signal component, and the switching means establishing in the expander setting a second loop from a point in the main path, through the further path, to the combining means such that the further signal component boosts the main signal component, the point in the main path to which the input of the further path is connected being on opposite sides of the point in the main path at which the further signal component is combined with the main signal component in the compressor and expander settings respectively, the further path including circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the dynamic range of the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 16

A circuit according to claim 9, wherein the main path includes a single combining means to which the output of the further path is permanently connected, and wherein the switching means connect the input to the further path to a first point in the main path preceding the single combining means in the compressor setting and connect the input to the further path to a second point in the main path following the single combining means in the expander setting.

Claim 17

A circuit according to claim 9, wherein the main path includes first followed by second combining means, the input to the further path is permanently connected to a point between the first and second combining means, and wherein the switching mEans connect the output of the further path to the second and first combining means in the compressor and expander settings respectively.

Claim 18

A circuit according to claim 9, wherein the main path includes a single combining means to which the output of the further path is permanently connected, and wherein the switching means connect the input to the further path to a first point in the main path following the single combining means in the compressor setting and connect the input to the further path to a second pint in the main path preceding the single combining means in the expander setting.

Claim 19

A circuit according to claim 9, wherein the main path includes first followed by second combining means, the input to the further path is permanently connected to a point between the first and second combining means, and wherein the switching means connect the output of the further path to the first and second combining means in the compressor and expander settings respectively.

Claim 20

A circuit for modifying the dynamic range of a signal, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, a further path having an input connected to a point in the main path and an output connected to the combining means for combining a further signal component with the main signal component, and a control circuit responsive to a signal in one of said paths to derive a smoothed control signal, the further path including controlled impedance means determining the transfer of a signal from the further path input to the further path output, the controlled impedance means being so responsive to the control signal that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 21

A circuit for modifying the dynamic range of a signal, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, a further path having an input connected to a point in the main path and an output connected to the combining means for combining a further signal component with the main signal component, and a control circuit responsive to a signal in one of said paths to derive a smoothed control signal, the further path including controlled impedance means determining the transfer of a signal from the further path input to the further path output, the controlled impedance means being so responsive to the control signal that, above a predetermined threshold, the dynamic range of the further signal component is linear with respect to the signal at the input to the further path, and, below the threshold, the gain of the further signal component relative to the signal at the input to the further path falls as the level of the last said signal falls.

Claim 22

A circuit according to claim 14, wherein the further signal component bucks the main signal component, whereby the circuit acts as a compressor.

Claim 23

A circuit according to claim 14, wherein the further signal component boosts the main signal component, whereby the circuit acts as an expander.

Claim 24

A circuit according to claim 14, wherein the controlled impedance means lies in series between the input to and the output of the further path, and the control signal reduces the impedance of the controlled impedance means as the level of the signal at the input to the further path increases.

Claim 25

A circuit according to claim 17, wherein the controlled impedance means is shunted by limiting means arranged to conduct when the signal level at the input to the further path increases abruptly.

Claim 26

A circuit according to claim 17, wherein the controlled impedance means is shunted by a filter which excludes the dynamic range modification in one or more pass-bands thereof.

Claim 27

A circuit according to claim 19, wherein the controlled impedance means acts as part of the series arm impedance of the filter and at least one stop band of the filter narrows as the impedance of the controlled impedance means is reduced.

Claim 28

A circuit according to claim 19, wherein the control circuit derives the smoothed control signal from the voltage developed across the filter.

Claim 29

A circuit according to claim 19, wherein the control circuit comprises a second filter complementary to the first said filter connected to the input to the further path and a smoothing circuit connected to the output of the second filter.

Claim 30

A circuit according to claim 14, wherein the further path includes a series impedance means, the controlled impedance means is connected as a shunt arm to form a potential divider with the series impedance means, tHe further path output is coupled to the junction of the series impedance means and the controlled impedance means, and the control signal increases the impedance of the controlled impedance means as the level of the signal at the input to the further path increases.

Claim 31

A circuit according to claim 23, wherein the series impedance means is shunted by limiting means arranged to conduct when the signal level at the input to the further path increases abruptly.

Claim 32

A circuit according to claim 14, wherein the further path comprises a variable gain amplifier whose gain is determined by the controlled impedance means.

Claim 33

A circuit according to claim 25, wherein the gain of the amplifier rises as the impedance of the controlled impedance means falls and wherein the control signal reduces the impedance of the controlled impedance means as the level of the signal at the input to the further path increases.

Claim 34

A circuit according to claim 26, wherein the controlled impedance means is shunted by limiting means arranged to conduct when the signal level at the input to the further path increases abruptly.

Claim 35

A circuit according to claim 25, wherein the variable gain amplifier is shunted by a filter which excludes the dynamic range modification in one or more pass-bands thereof.

Claim 36

A circuit according to claim 28, wherein the control circuit derives the smoothed control signal from the voltage developed across the filter.

Claim 37

A circuit for modifying the dynamic range of a signal, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, and a further path having an input connected to a point in the main path and an output connected to the combining means for combining a further signal component with the main signal component, wherein the further path comprises a plurality of circuit means connected in series, each circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the signal passed thereby is linear with respect to the dynamic range of the signal at the input to the circuit means, and, below the threshold, the gain of the signal passed thereby relative to the signal at the input to the circuit means falls as the level of the last said signal falls, and a plurality of filters, each shunting a respective one of the circuit means, the filters having different stop bands.

Claim 38

A circuit for modifying the dynamic range of a signal, comprising a main signal path including a combining means and extending from an input terminal to an output terminal for transferring to the output terminal a main signal component whose dynamic range is linear with respect to the dynamic range of an input signal applied to the input terminal, and a further path having an input connected to a point in the main path and an output connected to the combining means for combining a further signal component with the main signal component, wherein the further path comprises a plurality of circuit means connected in series, each circuit means having the characteristics of a conveyor such that, above a predetermined threshold, the dynamic range of the signal passed thereby is linear with respect to the dynamic range of the signal at the input to the circuit means, and, below the threshold, the gain of the signal passed thereby relative to the signal at the input to the circuit means falls as the level of the last said signal falls, and a plurality of filters, each shunting a respective one of the circuit means, the filters having different stop bands.

Claim 39

A circuit arrangement comprising a first circuit for processing a signal before the signal is applied to an information channel and a second circuit for reciprocally processing the signal derived from the information channel, wherein one circuit includes a processing network connected in a negative feedback loop of open loop gain A and the other circuit includes a substantially identical processing network in a first forward signal path which is in parallel with a linear, second forward signal path whose gain, relative to the said first forward path, is 1/A, the value of 1/A being such that the second forward path contributes a signal component which is small compared with that contributed by the first forward path.

Claim 40

A circuit arrangement comprising a first circuit for processing a signal before the signal is applied to an information channel and a second circuit for reciprocally processing the signal derived from the information channel, wherein one circuit includes a processing network connected in a negative feedback loop of open loop gain A and the other circuit includes a substantially identical processing network in a first forward signal path which is in parallel with a linear, second forward signal path whose gain, relative to the said first forward path, is 1/A, the value of 1/A being such that the second forward path contributes a signal component which is small compared with that contributed by the first forward path.

Claim 41

A circuit arrangement according to claim 31, wherein the processing network is an equalizing network.

Claim 42

A circuit arrangement according to claim 31, wherein the said one and other circuits are the first and second circuits respectively, and the processing network is a signal expander.

Claim 43

A circuit arrangement according to claim 31, wherein the said one and other circuits are the second and first circuits respectively.

Claim 44

A circuit arrangement according to claim 34, wherein the processing network is a signal compressor.

Claim 45

A circuit arrangement comprising a first circuit for processing a signal before the signal is applied to an information channel and a second circuit for reciprocally processing the signal derived from the information channel, wherein one circuit includes a processing network which is linear with respect to dynamic range connected in a negative feedback loop of open loop gain A and the other circuit includes a substantially identical processing network in a first forward signal path which is in parallel with a linear, second forward signal path whose gain, relative to the said first forward path, is 1/A.

Claim 46

A circuit arrangement comprising a first circuit for processing a signal before the signal is applied to an information channel and a second circuit for reciprocally processing the signal derived from the information channel, wherein one circuit includes a processing network which is linear with respect to dynamic range connected in a negative feedback loop of open loop gain A and the other circuit includes a substantially identical processing network in a first forward signal path which is in parallel with a linear, second forward signal path whose gain, relative to the said first forward path, is 1/A.

Claim 47

A circuit arrangement according to claim 36, wherein the value of 1/A is such that the second forward path contributes a signal component which is small compared with that contributed by the first forward path.

Claim 48

A circuit arrangement according to claim 36, wherein the said one and other circuits are the second and first circuits respectively.

Claim 49

A circuit arrangement according to claim 36, wherein the processing network is an equalizing network.