Dynamic balance control for telephone
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. A dynamic balance control circuit maintains the transmit and receive channels in a predetermined energy ratio during double talk.
1. In a telephone including an audio frequency circuit having a transmit channel and a receive channel, an acoustic echo canceling circuit, a line echo canceling circuit, and a noise reduction circuit coupled to the channels, and wherein each 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 led one to each sub-band filter, wherein each voice activity detector produces a signal indicative of the energy content of an input signal to the detector;
a plurality of variable gain amplifiers coupled one each to a voice activity detector in the receive channel;
a plurality of comparators coupled one each to a pair of voice activity detectors, wherein each pair includes a voice activity detector from the transmit channel and the variable gain amplifier from the corresponding voice activity detector coupled to the receive channel;
means for controlling the gain of said variable gain amplifiers to provide a predetermined balance between the channels, said means including:
a first averaging circuit coupled to the output of the acoustic echo canceller;
a second averaging circuit coupled to the output of the line echo canceller; and
a ratio detector coupled to the first averaging circuit and the second averaging circuit;
wherein said means controls gain in accordance with the ratio of the averages of the outputs of the acoustic echo canceling circuit and the line echo canceling circuit.
2. The telephone as set forth in claim 1 wherein each averaging circuit averages an input signal only when the input signal exceeds a predetermined threshold.
3. The telephone as set forth in claim 2 wherein the predetermined thresholds are determined separately for each averaging circuit.
4. The telephone as set forth in claim 1 wherein each averaging circuit averages amplitude.
5. The telephone as set forth in claim 1 wherein each averaging circuit averages energy.
6. In a telephone including an audio frequency circuit having a transmit channel having variable gain and a receive channel having variable gain, an acoustic echo canceling circuit, and a line echo canceling circuit, the improvement comprising:
a first averaging circuit coupled to the output of the acoustic echo canceller;
a second averaging circuit coupled to the output of the line echo canceller; and
a ratio detector coupled to the first averaging circuit and the second averaging circuit;
wherein the output of the ratio detector controls gain in each channel.
7. The telephone as set forth in claim 6 wherein each averaging circuit averages an input signal only when the input signal exceeds a predetermined threshold.
8. The telephone as set forth in claim 7 wherein the predetermined thresholds are determined separately for each averaging circuit.
9. The telephone as set forth in claim 8 and further including:
a first broad band voice activity detector coupled to said acoustic echo canceller and to said first averaging circuit for controlling the averaging of the output signal from the acoustic echo canceller;
a second broad band voice activity detector coupled to said line echo canceller and to said second averaging circuit for controlling the averaging of the output signal from the line echo canceller.
10. The telephone as set forth in claim 9 wherein each 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 an 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.
11. The telephone asset forth in claim 10 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 .
12. The telephone as set forth in claim 11 wherein a fourth of said threshold detectors is coupled to E out and compares E out with a noise threshold.
13. The telephone as set forth in claim 12 wherein said telephone is a cellular telephone and further includes radio frequency circuitry coupled to said audio frequency circuitry.