Adaptive gain and filtering circuit for a sound reproduction system

A programmable compressive gain amplifier circuit comprising:

• a first amplifier for receiving an input signal in the audible frequency range and for producing an amplified signal;
• means for establishing a threshold level for the amplified signal;
• a gain register for storing a gain value;
• means, responsive to the amplified signal and the threshold level, for increasing the gain value when the amplified signal falls below the threshold level and for decreasing the gain value when the amplified signal rises above the threshold level;
• wherein the first amplifier is responsive to the gain register for varying the gain of the first amplifier as a function of the gain value;
• a second amplifier for receiving the input signal and for producing an output signal;
• and
• means for programming the gain of the second amplifier as a function of the gain value,
• wherein the output signal is programmably compressed.

An adaptive gain amplifier circuit comprising:

• an amplifier for receiving an input signal in the audible frequency range and producing an output signal;
• a gain register for storing a gain value;
• a preamplifier having a preset gain for amplifying the gain value to produce a gain signal;
• wherein the amplifier is responsive to the preamplifier for varying the gain of the amplifier as a function of the gain signal;
• means for establishing a threshold level for the output signal;
• and
• means, responsive to the output signal and the threshold level, for increasing the gain value up to a predetermined limit when the output signal falls below the threshold level and for decreasing the gain value when the output signal rises above the threshold level,
• wherein the output signal is adaptively compressed.

An adaptive gain amplifier circuit comprising:

• an amplifier for receiving an input signal in the audible frequency range and producing an output signal;
• means for establishing a threshold level for the output signal;
• a gain register for storing a gain value;
• and
• means, responsive to the output signal and the threshold level, for increasing the gain value in increments having a first preset magnitude when the output signal falls below the threshold level and for decreasing the gain value in decrements having a second preset magnitude when the output signal rises above the threshold level;
• wherein the gain register stores the gain value as a first plurality of least significant bits and as a second plurality of most significant bits;
• wherein the first preset magnitude comprises a number of bits less than or equal to a total number of bits comprising the least significant bits;
• wherein the gain register outputs the most significant bits of the gain value to the amplifier for controlling the gain of the amplifier;
• and
• wherein the output signal is compressed as a function of the ratio of the second preset magnitude over the first preset magnitude to produce an adaptively compressed output signal.

An adaptive gain amplifier circuit comprising a plurality of channels connected to a common output, each channel comprising:

• a filter with preset parameters for receiving an input signal in the audible frequency range for producing a filtered signal;
• a channel amplifier responsive to the filtered signal for producing a channel output signal;
• a channel gain register for storing a gain value;
• a channel preamplifier having a preset gain for amplifying the gain value to produce a gain signal;
• wherein the channel amplifier is responsive to the channel preamplifier for varying the gain of the channel amplifier as a function of the gain signal;
• means for establishing a channel threshold level for the channel output signal;
• and
• means, responsive to the channel output signal and the channel threshold level, for increasing the gain value up to a predetermined limit when the channel output signal falls below the channel threshold level and for decreasing the gain value when the channel output signal rises above the channel threshold level;
• wherein the channel output signals are combined to produce an adaptively compressed and filtered output signal.

An adaptive gain amplifier circuit comprising:

• a plurality of channels connected to a common output, each channel comprising:
• a filter with preset parameters for receiving an input signal in the audible frequency range and for producing a filtered signal;
• a channel amplifier responsive to the filtered signal for producing a channel output signal;
• means for establishing a channel threshold level for the channel output signal;
• a comparator for producing a control signal as a function of the level of the channel output signal being greater or less than the channel threshold level;
• a channel gain register for storing a gain setting;
• an adder responsive to the control signal for increasing the gain setting by a first preset magnitude when the channel output signal falls below the channel threshold level and for decreasing the gain setting by a second preset magnitude when the channel output signal rises above the channel threshold level;
• and
• a second channel gain register for storing a predetermined channel gain value to define an operating range for the channel as a function of a signal level of the input signal;
• wherein the channel amplifier is responsive to the gain register and to the second channel gain register for varying the gain of the channel amplifier as a function of the gain setting and the predetermined channel gain value;
• and
• wherein the channel output signals are combined to produce an adaptively compressed and filtered output signal.