Distributed VAD control system for telephone

Abstract

A telephone includes a transmit channel and a receive channel, each including a bank of sub-band filters having a VAD coupled one to each sub-band filter. Each VAD measures the spectral energy in a sub-band, compares the spectral energy to a first threshold, and produces an output signal representative of whether or not the first threshold is exceeded. The voice activity detector also includes a threshold circuit for calculating a dynamically adjustable noise threshold based upon averaged measured spectral energy. A wide band or system VAD monitors echo canceling circuitry to detect voice activity and double talk.

What is claimed as the invention is:  
     
         1 . In a telephone including noise reduction circuitry having a plurality of sub-band filters in at least one channel, the improvement comprising: 
 a plurality of voice activity detectors coupled one to each sub-band filter.    
     
     
         2 . The telephone as set forth in  claim 1  wherein the telephone includes a transmit channel and a receive channel, each channel including a bank of sub-band filters, wherein the improvement comprises: 
 a plurality of voice activity detectors coupled one to each sub-band filter.  
 
     
     
         3 . The telephone as set forth in  claim 1  wherein each voice activity detector includes: 
 a first circuit for calculating the spectral energy in a sub-band; and  
 a comparator for comparing the spectral energy with a first threshold and producing an output signal indicative of whether or not the first threshold is exceeded.  
 
     
     
         4 . The telephone as set forth in  claim 3  and further including a fast attack, slow release circuit coupled to said comparator.  
     
     
         5 . The telephone as set forth in  claim 3  wherein first threshold is a noise threshold and said voice activity detector further includes averaging circuit coupled to said first circuit, said averaging circuit calculating said noise threshold.  
     
     
         6 . The telephone as set forth in  claim 5  wherein the output signal from said comparator is coupled to said threshold circuit and causes the averaging circuit to average spectral energy only when the output signal indicates that said first threshold has not been exceeded.  
     
     
         7 . The telephone as set forth in  claim 6  wherein the output signal from said comparator causes the averaging circuit to average the noise threshold when the output signal indicates that said first threshold has been exceeded.  
     
     
         8 . The telephone as set forth in  claim 5  and further including a timing circuit coupled to said averaging circuit for causing said averaging circuit to average spectral energy at least once every predetermined period.  
     
     
         9 . The telephone as set forth in  claim 5  and further comprising a first broad band voice activity detector in the transmit channel coupled to the sub-band voice activity detectors in the transmit channel.  
     
     
         10 . The telephone as set forth in  claim 9  and further comprising a second broad band voice activity detector in the receive channel coupled to the sub-band voice activity detectors in the receive channel.  
     
     
         11 . A telephone comprising: 
 a signal processing circuit, including 
 an audio processing circuit, including 
 an echo canceling and noise reduction circuit, including 
 a first circuit for calculating spectral energy; and  
 a comparator for comparing the spectral energy to a first threshold and producing an output signal indicative of whether or not the first threshold is exceeded;  
 an averaging circuit coupled to said first circuit and to said comparator, said averaging circuit calculating said first threshold.  
 
 
   
     
     
         12 . The telephone as set forth in  claim 11  wherein the output signal from said comparator causes the averaging circuit to average spectral energy only when the output signal has a first value.  
     
     
         13 . The telephone as set forth in  claim 12  wherein the first value indicates that the spectral energy is below the first threshold.  
     
     
         14 . The telephone as set forth in  claim 13  and further including a timing circuit coupled to said averaging circuit for causing said averaging circuit to average spectral energy at least once every predetermined period even when the output signal has a second value.  
     
     
         15 . In a telephone including an audio frequency circuit having a transmit channel and a receive channel, an echo canceling circuit and a noise reduction circuit coupled to the channels, and wherein at least one channel includes a filter bank for dividing the channel into a plurality of sub-bands, the improvement comprising: 
 a plurality of voice activity detectors coupled one to each sub-band filter; and    a broad band voice activity detector coupled to said echo canceling circuit.    
     
     
         16 . The telephone as set forth in  claim 15  wherein said broad band voice activity detector includes: 
 a plurality of threshold detectors;  
 an AND circuit having a plurality of inputs coupled one to each of said threshold detectors;  
 a ratio detector coupled to said echo canceling circuit for calculating the following ratio  
               E     i                 n       ·     E   out           E     i                 n     2     +     E   echo   2         ;                   
 where E in  is the signal at the input to the echo canceling circuit, E out  is the signal output from the echo canceling circuit, and E echo  is the echo estimate generated by the echo canceling circuit; and  
 wherein a first of said threshold detectors is coupled to the output of said ratio detector.  
 
     
     
         17 . The telephone as set forth in  claim 16  wherein a second of said threshold detectors is coupled to E in , a third of said threshold detectors is coupled to both E in  and E out .  
     
     
         18 . The telephone as set forth in  claim 17  wherein a fourth of said threshold detectors is coupled to E out  and compares E out  with a noise threshold.  
     
     
         19 . The telephone as set forth in  claim 15  wherein said telephone is a cellular telephone and further includes radio frequency circuitry coupled to said audio frequency circuitry.