Compressor and expander circuits having control network responsive to signal level in circuit

Claim 2

A signal compressor circuit for reducing, within a predetermined input dynamic range, the dynamic range of an input signal, comprising first and second circuit paths for conducting signal components from an input terminal to an output terminal, each circuit path being linear with respect to dynamic range in its operation, variable combining means coupling the two circuit paths to the output terminal, and a control circuit responsive to the signal level of a signal in the compressor circuit automatically to control the variable combining means so that at low and high levels of the predetermined input dynamic range the signal reaching the output terminal is contributed substantially completely by the first and second circuit paths respectively, whereas at intermediate levels of the predetermined range the signal reaching the output terminal comprises components contributed by both circuit paths, the circuit path gains and the combining means being so arranged that the output signal is boosted at low levels relative to the output signal at high levels.

Claim 3

A signal compressor circuit according to claim 1, wherein there are more than two paths and wherein the variable combining means selects the relative proportions in which the outputs of the paths contribute to the output signal in dependence upon the said signal level.

Claim 4

A signal compressor circuit according to claim 1, wherein the combining means comprise a fixed impedance connected between the first path and the output terminal, and a variable impedanCe connected between the second path and the output terminal, and wherein the control circuit is arranged to control the variable impedance so that the impedance thereof is very high and very low, compared with the fixed impedance, when the input signal has a low or high level respectively.

Claim 5

A signal compressor circuit according to claim 1, wherein the control circuit which controls the variable combining means includes a first smoothing circuit with a relatively short time constant, followed by a second smoothing circuit having a relatively long time constant under steady signal conditions but having a relatively short time constant when the signal level changes abruptly.

Claim 6

A signal compressor circuit according to claim 1, wherein the variable combining means has coupled thereto non-linear limiting means adapted to limit the combining means signal to a small value under transient input signal conditions.

Claim 7

A signal compressor circuit according to claim 1, wherein the variable combining means is non-linear in its operation.

Claim 8

A signal circuit compressor according to claim 1, wherein at least one of the paths includes a filter with predetermined characteristics, whereby the compressor circuit acts as a frequency selective compressor.

Claim 9

A signal compressor circuit according to claim 7, wherein at least one of the filters is adapted to reject a carrier frequency.

Claim 10

A signal expander circuit for increasing, within a predetermined input dynamic range, the dynamic range of an input signal, comprising first and second circuit paths for conducting signal components from an input terminal to an output terminal, each circuit path being linear with respect to dynamic range in its operation, the second circuit path including a filter with predetermined characteristics, variable combining means coupling the two circuit paths to the output terminal, and a control circuit responsive to the signal level of a signal in the expander circuit automatically to control the variable combining means so that, at low and high levels of the predetermined input dynamic range, the signal reaching the output terminal is contributed substantially completely by the first and second circuit paths respectively, whereas at intermediate levels of the predetermined range the signal reaching the output terminal comprises components contributed by both circuit paths, the circuit path gains and the combining means being so arranged that the output signal in at least part of the frequency band is attenuated at low levels relative to the output signal at high levels.

Claim 11

A signal expander circuit for increasing, within a predetermined input dynamic range, the dynamic range of an input signal, comprising first and second circuit paths for conducting signal components from an input terminal to an output terminal, each circuit path being linear with respect to dynamic range in its operation, the second circuit path including a filter with predetermined characteristics, variable combining means coupling the two circuit paths to the output terminal, and a control circuit responsive to the signal level of a signal in the expander circuit automatically to control the variable combining means so that, at low and high levels of the predetermined input dynamic range, the signal reaching the output terminal is contributed substantially completely by the first and second circuit paths respectively, whereas at intermediate levels of the predetermined range the signal reaching the output terminal comprises components contributed by both circuit paths, the circuit path gains and the combining means being so arranged that the output signal in at least part of the frequency band is attenuated at low levels relative to the output signal at high levels.

Claim 12

A signal expander circuit according to claim 9, wherein the first circuit path is linear with respect to frequency in its operation.

Claim 13

A signal expander circuit according to claim 9, wherein the first circuit path also includes a filter with predetermined characteristics.

Claim 14

A signal expander circuit according to claim 9, wherein there are more than two paths and wherein the variable combining means selects the relative proportions in which the outputs of the paths contribute to the output signal in dependence upon the said signal level.

Claim 15

A signal expander circuit according to claim 9, wherein the combining means comprise a fixed impedance connected between the first path and the output terminal, and a variable impedance connected between the second path and the output terminal, and wherein the control circuit is arranged to control the variable impedance so that the impedance thereof is very high and very low, compared with the fixed impedance, when the input signal has the low and high levels respectively.

Claim 16

A signal expander circuit according to claim 9, wherein the control circuit which controls the variable combining means includes a smoothing circuit with a relatively short time constant, followed by a second smoothing circuit having a relatively long time constant under steady signal conditions but having a relatively short time constant when the signal level changes abruptly.

Claim 17

A signal exPander circuit according to claim 9, wherein the variable combining means has coupled thereto non-linear limiting means adapted to limit the combining means signal to a small value under transient input signal conditions.

Claim 18

A signal expander circuit according to claim 9, wherein the filter is adapted to reject a carrier frequency.

Claim 19

A signal expander circuit according to claim 9, wherein the variable combining means is non-linear in its operation.

Claim 20

A signal expander circuit for increasing, within a predetermined input dynamic range, the dynamic range of an input signal, comprising first and second circuit paths for conducting signal components from an input terminal to an output terminal, each circuit path being linear with respect to dynamic range in its operation, a filter with predetermined characteristics in the first circuit path, variable combining means coupling the two circuit paths to the output terminal and a control circuit responsive to the current through or voltage across a variable element of the variable combining means automatically to control the variable combining means so that, at low and high levels of the predetermined input dynamic range, the signal reaching the output terminal is contributed substantially completely by the first and second circuit paths respectively, whereas at intermediate levels of the predetermined range the signal reaching the output terminal comprises components contributed by both circuit paths, the circuit path gains and the combining means being so arranged that the output signal in at least part of the frequency band is attenuated at low levels relative to the output signal at high levels.

Claim 21

A signal expander circuit for increasing, within a predetermined input dynamic range, the dynamic range of an input signal, comprising first and second circuit paths for conducting signal components from an input terminal to an output terminal, each circuit path being linear with respect to dynamic range in its operation, a filter with predetermined characteristics in the first circuit path, variable combining means coupling the two circuit paths to the output terminal and a control circuit responsive to the current through or voltage across a variable element of the variable combining means automatically to control the variable combining means so that, at low and high levels of the predetermined input dynamic range, the signal reaching the output terminal is contributed substantially completely by the first and second circuit paths respectively, whereas at intermediate levels of the predetermined range the signal reaching the output terminal comprises components contributed by both circuit paths, the circuit path gains and the combining means being so arranged that the output signal in at least part of the frequency band is attenuated at low levels relative to the output signal at high levels.

Claim 22

A signal expander circuit according to claim 18, wherein there are more than two paths and wherein the variable combining means selects the relative proportions in which the outputs of the paths contribute to the output signal in dependence upon the said one or more signal levels, or difference in levels.

Claim 23

A signal expander circuit according to claim 18, wherein the combining means comprise a fixed impedance connected between the first path and the output terminal, and a variable impedance connected between the second path and the output terminal, and wherein the control circuit is aranged to control the variable impedance so that the impendance thereof is very high and very low, compared with impednace fixed impedance, when the input signal has the low and high levels respectively.

Claim 24

A signal expander circuit according to claim 18, wherein the control circuit which controls the variable combining means includes a smoothing circuit with a relatively short time constant, followed by a second smoothing circuit having a relatively long time constant under steady signal conditions but having a relatively short time constant when the signal level changes abruptly.

Claim 25

A signal expander circuit according to claim 18, wherein the variable combining means has coupled thereto non-linear limiting means adapted to limit the combining means signal to a small value under transient input signal conditions.

Claim 26

A signal expander circuit according to claim 18, wherein the filter is adapted to reject a carrier frequency.

Claim 27

A signal expander circuit according to claim 18, wherein the variable combining means is non-linear in its operation.