Compression and expansion system using a subtraction circuit

Claim 2

A compression system comprising: frequency characteristic changing means for changing the frequency characteristic thereof in a manner such that, with respect to an input signal, the level of the high frequency band signal thereof is relatively increased as the level of the input signal is low; subtraction means for carrying out subtraction operation of an input to the frequency characteristic changing means and the output signal of said frequency characteristic changing means; and frequency characteristic control means supplied with the resulting output of the subtraction means and operating to supply a control signal for changing the frequency characteristic to the frequency characteristic changing means, said subtraction means producing as output a signal of equivalently high-pass filtering characteristic of which cut-off frequency varies in accordance with the level of the input signal.

Claim 3

An expansion system for expanding a transmitted signal compressed by the compression system according to claim 1, comprising: second frequency characteristic changing means for changing the frequency characteristic thereof in a manner to cause a decrease relatively in the level of the high frequency bAnd signal of the signal thus transmitted; second subtraction means for carrying out subtraction operation of an input signal to the second frequency characteristic changing means and the output signal of said second frequency characteristic changing means; and second frequency characteristic control means supplied with the resulting output of the second subtraction means and operating to supply a control signal for changing the frequency characteristic to the second frequency characteristic changing means.

Claim 4

A compressing and expansion system comprising: first frequency characteristic changing means for changing the frequency characteristic thereof in a manner such that, with with respect to an input signal, the level of the high frequency band signal thereof is relatively increased as the level of the input signal is low; first subtraction means for carrying out subtraction operation of an input signal to the first frequency characteristic changing means and the output signal of said frequency characteristic changing means; first frequency characteristic control means supplied with the resulting output of the first subtraction means and operating to supply a control signal for changing the frequency characteristic to the first frequency characteristic changing means; second frequency characteristic changing means for changing the frequency characteristic thereof in a manner to cause a decrease relatively in the level of the high frequency band signal of a signal produced as output and transmitted from the first frequency characteristic changing means; second subtraction means for carrying out subtraction operation of an input signal to the second frequency characteristic changing means and the output signal of said second frequency characteristic changing means; and second frequency characteristic control means supplied with the resulting output of the second subtraction means and operating to supply a control signal for changing the frequency characteristic to the second frequency characteristic changing means, said first and second subtraction means producing respectively as output signals which are equivalently of high-pass filtering characteristic of which cut-off frequencies vary in accordance with the level of the input signal.

Claim 5

A compressing and expansion system comprising: first frequency characteristic changing means for changing the frequency characteristic thereof in a manner such that, with with respect to an input signal, the level of the high frequency band signal thereof is relatively increased as the level of the input signal is low; first subtraction means for carrying out subtraction operation of an input signal to the first frequency characteristic changing means and the output signal of said frequency characteristic changing means; first frequency characteristic control means supplied with the resulting output of the first subtraction means and operating to supply a control signal for changing the frequency characteristic to the first frequency characteristic changing means; second frequency characteristic changing means for changing the frequency characteristic thereof in a manner to cause a decrease relatively in the level of the high frequency band signal of a signal produced as output and transmitted from the first frequency characteristic changing means; second subtraction means for carrying out subtraction operation of an input signal to the second frequency characteristic changing means and the output signal of said second frequency characteristic changing means; and second frequency characteristic control means supplied with the resulting output of the second subtraction means and operating to supply a control signal for changing the frequency characteristic to the second frequency characteristic changing means, said first and second subtraction means producing respectively as output signals which are equivalently of high-pass filtering characteristic of which cut-off frequencies vary in accordance with the level of the input signal.

Claim 6

A compression circuit comprising: a frequency characteristic changing circuit for changing the frequency characteristic thereof in a manner such that, with respect to an input signal, the level of the high frequency band signal thereof is relatively increased as the level of the input signal is low; a subtraction circuit for carrying out subtraction operation of an input to the frequency characteristic changing circuit and the output of said frequency characteristic changing circuit; and a frequency characteristic control circuit supplied with the resulting output of the subtraction circuit and operating to supply a control signal for changing the frequency characteristic to the frequency characteristic changing circuit, said subtraction circuit producing as output a signal of equivalently high-pass filtering characteristic of which cut-off frequency varies in accordance with the level of the input signal.

Claim 7

A compression circuit comprising: a frequency characteristic changing circuit for changing the frequency characteristic thereof in a manner such that, with respect to an input signal, the level of the high frequency band signal thereof is relatively increased as the level of the input signal is low; a subtraction circuit for carrying out subtraction operation of an input to the frequency characteristic changing circuit and the output of said frequency characteristic changing circuit; and a frequency characteristic control circuit supplied with the resulting output of the subtraction circuit and operating to supply a control signal for changing the frequency characteristic to the frequency characteristic changing circuit, said subtraction circuit producing as output a signal of equivalently high-pass filtering characteristic of which cut-off frequency varies in accordance with the level of the input signal.

Claim 8

A compression circuit as claimed in claim 4 in which said subtraction circuit comprises a differential amplifier having two input terminals and supplied respectively through the input terminals with the input and output of the frequency characteristic changing circuit.

Claim 9

A compression circuit as claimed in claim 5 in which said frequency characteristic control circuit includes a rectifying circuit for rectifying the output of the differential amplifier and supplying the resulting rectified output thereof to the frequency characteristic changing circuit.

Claim 10

A compression circuit as claimed in claim 4 in which said frequency characteristic changing circuit has a field-effect transistor having a gate to which is applied the output control signal of the frequency characteristic contrOl circuit whereby the internal impedance thereof is varied, and which changes the frequency characteristic of the input signal.

Claim 11

An expansion circuit for expanding a transmitted signal compressed by the compression circuit according to claim 4, comprising: second frequency characteristic changing circuit for changing the frequency characteristic thereof in a manner to cause a decrease relatively in the level of the high frequency band signal of the signal thus transmitted; second subtraction circuit for carrying out subtraction operation of an input signal to the second frequency characteristic changing circuit and the output signal of said second frequency characteristic changing circuit; and second frequency characteristic control circuit supplied with the resulting output of the second subtraction circuit and operating to supply a control signal for changing the frequency characteristic to the second frequency changing circuit.

Claim 12

An expansion circuit as claimed in claim 8 in which said second subtraction circuit comprises a second differential amplifier having two input terminals and supplied respectively through the input terminals with the input and output of the second frequency characteristic changing circuit.

Claim 13

An expansion circuit as claimed in claim 9 in which said second frequency characteristic control circuit includes a second rectifying circuit for rectifying the output of the second differential amplifier and supplying the resulting rectified output thereof to the second frequency characteristic changing circuit.

Claim 14

An expansion circuit as claimed in claim 8 in which said second frequency characteristic changing circuit has a second field-effect transistor having a gate to which is applied the output control signal of the second frequency characteristic control circuit whereby the internal impedance thereof is varied, and which changes the frequency characteristic of the input signal.

Claim 15

A compressing and expansion circuit comprising: first frequency characteristic changing circuit for changing the frequency characteristic thereof in a manner such that, with respect to an input signal, the level of the high frequency band signal thereof is relatively increased as the level of the input signal is low; first subtraction circuit for carrying out subtraction operation of an input signal to the first frequency characteristic changing circuit and the output signal of said frequency characteristic changing circuit; first frequency characteristic control circuit supplied with the resulting output of the first subtraction circuit and operating to supply a control signal for changing the frequency characteristic to the first frequency characteristic changing circuit; second frequency characteristic changing circuit for changing the frequency characteristic thereof in a manner to cause a decrease relatively in the level of the high frequency band signal of a signal produced as output and transmitted from the first frequency characteristic changing circuit; second subtraction circuit for carrying out subtraction operation of an input signal to the second frequency characteristic changing circuit and the output signal of said second frequency characteristic changing circuit; and second frequency characteristic control circuit supplied with the resulting output of the second subtraction circuit and operating to supply a control signal for changing the frequency characteristic to the second frequency characteristic changing circuit, said first and second subtraction circuits producing respectively as output signals which are equivalently of high-pass filtering characteristic of which cut-off frequencies vary in accordance with the level of the input signal.

Claim 16

A compressing and expansion circuit comprising: first frequency characteristic changing circuit for changing the frequency characteristic thereof in a manner such that, with respect to an input signal, the level of the high frequency band signal thereof is relatively increased as the level of the input signal is low; first subtraction circuit for carrying out subtraction operation of an input signal to the first frequency characteristic changing circuit and the output signal of said frequency characteristic changing circuit; first frequency characteristic control circuit supplied with the resulting output of the first subtraction circuit and operating to supply a control signal for changing the frequency characteristic to the first frequency characteristic changing circuit; second frequency characteristic changing circuit for changing the frequency characteristic thereof in a manner to cause a decrease relatively in the level of the high frequency band signal of a signal produced as output and transmitted from the first frequency characteristic changing circuit; second subtraction circuit for carrying out subtraction operation of an input signal to the second frequency characteristic changing circuit and the output signal of said second frequency characteristic changing circuit; and second frequency characteristic control circuit supplied with the resulting output of the second subtraction circuit and operating to supply a control signal for changing the frequency characteristic to the second frequency characteristic changing circuit, said first and second subtraction circuits producing respectively as output signals which are equivalently of high-pass filtering characteristic of which cut-off frequencies vary in accordance with the level of the input signal.

Claim 17

A compression and expansion circuit as defined in claim 12 in which said second frequency characteristic changing circuit has substantially the same circuit construction as the first frequency characteristic changing circuit, said second subtraction cIrcuit has substantially the same circuit construction as the first subtraction circuit, and said second frequency characteristic control circuit has substantially the same circuit construction as the first frequency characteristic control circuit.