Noise reduction circuit for telephones

In a noise reducing circuit for processing a pair of audio signals in two channels, wherein each channel includes a plurality of band pass filters for dividing the signal in each channel into a plurality of bands and a summation network in each channel for re-combining the outputs of the band pass filters, the improvement comprising:

• a plurality of threshold detectors coupled one each to the output of a band pass filter;
• control logic coupled to the threshold detectors;
• a plurality of variable gain amplifiers coupled one each to a band pass filter and to said control logic;
• wherein said control logic reduces the gain of selected variable gain amplifiers in accordance with the outputs of the threshold detectors but does not fully reduce the gain of amplifiers in adjacent bands in a given channel.

A noise reducing circuit for processing audio signals comprising:

• a plurality of band pass filters for dividing the signals into a plurality of bands;
• a plurality of first detectors coupled one each to a band pass filter, each first detector having a long response time;
• a plurality of variable gain amplifiers, each amplifier having an input coupled to a band pass filter, a control input, and an output;
• a summation circuit coupled to the outputs of the variable gain amplifiers;
• control logic coupled to said first detectors and to the control inputs of the variable gain amplifiers for preventing the signals in adjacent bands within a given channel from being fully attenuated simultaneously and for permitting the signals in adjacent bands within the given channel to be partially attenuated simultaneously.

In a conference telephone having an audio processing circuit including a noise reducing circuit for processing a pair of audio signals in two channels, wherein each channel includes a plurality of band pass filters for dividing the signal in each channel into a plurality of bands and a summation network for re-combining the outputs of the band pass filters, the improvement comprising:

• a plurality of threshold detectors coupled one each to the output of a band pass filter;
• control logic coupled to all the threshold detectors;
• a plurality of variable gain amplifiers coupled one each to a band pass filter and to said control logic;
• wherein said control logic reduces the gain of selected variable gain amplifiers in accordance with the outputs of all the threshold detectors but does not fully reduce the gain of amplifiers in adjacent bands in a given channel.

In a cellular telephone having an audio processing circuit including a noise reducing circuit for processing a pair of audio signals in two channels, wherein each channel includes a plurality of band pass filters for dividing the signal in each channel into a plurality of bands and a summation network for re-combining the outputs of the band pass filters, the improvement comprising:

• a plurality of threshold detectors coupled one each to the output of a band pass filter;
• control logic coupled to all the threshold detectors;
• a plurality of variable gain amplifiers coupled one each to a band pass filter and to said control logic;
• wherein said control logic reduces the gain of selected variable gain amplifiers in accordance with the outputs of all the threshold detectors but does not fully reduce the gain of amplifiers in adjacent bands in a given channel.

A hands free kit comprising:

• an audio processing circuit for processing a pair of audio signals in two channels, wherein each channel includes a plurality of band pass filters for dividing the signal in each channel into a plurality of bands and a summation network in each channel for re-combining the outputs of the band pass filters;
• a plurality of threshold detectors coupled one each to the output of a band pass filter;
• control logic coupled to all the threshold detectors;
• a plurality of variable gain amplifiers coupled one each to a band pass filter and to said control logic;
• wherein said control logic reduces the gain of selected variable gain amplifiers in accordance with the outputs of all the threshold detectors but does not fully reduce the gain of amplifiers in adjacent bands in a given channel.

In a desk telephone having an audio processing circuit including a noise reducing circuit for processing a pair of audio signals in two channels, wherein each channel includes a plurality of band pass filters for dividing the signal in each channel into a plurality of bands and a summation network for re-combining the outputs of the band pass filters, the improvement comprising:

• a plurality of threshold detectors coupled one each to the output of a band pass filter;
• control logic coupled to all the threshold detectors;
• a plurality of variable gain amplifiers coupled one each to a band pass filter and to said control logic;
• wherein said control logic reduces the gain of selected variable gain amplifiers in accordance with the outputs of all the threshold detectors but does not fully reduce the gain of amplifiers in adjacent bands in a given channel.