Speakerphone using digitally compressed audio to detect acoustic feedback

A method for detecting acoustic feedback in a speakerphone for a radiotelephone for communicating voice signals by way of a radio channel, said radiotelephone including radio means for transmitting a first signal including voice signals on the radio channel and receiving a second signal including voice signals from the radio channel, said speakerphone including microphone means for producing the first signal, speaker means for emitting the second signal, first amplifying means having an input coupled to said microphone means and an output coupled to said radio means and being responsive to first digital control signals for selecting one of a plurality of gain settings and amplifying the first signal, second amplifying means having an input coupled to said radio means and an output coupled to said speaker means and being responsive to second digital control signals for selecting one of a plurality of gain settings and amplifying the second signal, and processing means coupled to the output of said first amplifying means and the input of the second amplifying means, respectively, and, in response to detection of voice signals in one of the first and second signals, producing the first and second digital control signals for adjusting the gain settings of said first amplifying means and said second amplifying means such that the gain setting for said one of the first and second signals is increased to a nominal gain and the gain setting of the other of the first and second signals is decreased by a first predetermined gain, said method comprising the steps of:

• producing first and second digital samples of the output of the first amplifying means and the output the second amplifying means, respectively;
• monitoring a predetermined number of consecutive second digital samples;
• and
• reducing the first predetermined gain by a second predetermined gain if the predetermined number of consecutive second digital samples have magnitudes differing by less than a third predetermined gain.

A radiotelephone for communicating voice signals by way of a radio channel, comprising:

• microphone means for producing a first signal including voice signals;
• speaker means for emitting a second signal including voice signals;
• radio means for transmitting the first signal on and receiving the second signal from the radio channel;
• first amplifying means having an input coupled to said microphone means and an output coupled to said radio means and being responsive to first digital control signals for selecting one of a plurality of gain settings and amplifying the first signal;
• second amplifying means having an input coupled to said radio means and an output coupled to said speaker means and being responsive to second digital control signals for selecting one of a plurality of gain settings and amplifying the second signal;
• converting means for producing first and second digital samples of the output of the first amplifying means and the input of the second amplifying means, respectively;
• and
• processing means coupled to the first and second digital samples of said converting means for detecting voice signals in the first and second signals, respectively, and, in response to detection of voice signals in one of the first and second signals, producing the first and second digital control signals for adjusting the gain settings of said first amplifying means and said second amplifying means such that the gain setting for said one of the first and second signals is increased to a nominal gain and the gain setting of the other of the first and second signals is decreased by a first predetermined gain, and said processing means monitoring a prederermined number of consecutive second digital samples and reducing the first predetermined gain by a second predetermined gain if the predetermined number of consecutive second digital samples have magnitudes differing by less than a third predetermined gain.