An automatic squelch is provided within an intercom to control the gating of a microphone signal path. The automatic squelch includes an analog-to-digital converter coupled to receive an analog microphone input signal which is configured to convert the analog microphone input signal into a digital input signal. A peak detector is further provided to maintain a peak value indicative of peaks in the digital input signal. The peak value maintained by the peak detector reacts relatively quickly to changes in the digital input signal. In one implementation, when the digital input signal is larger than the peak value, the peak value is set at the level of the digital input signal. When the digital input signal is less than the peak value, the peak value is "decayed" or reduced at a relatively fast decay rate. A background noise detector is further provided for maintaining a background value indicative of background noise in the digital input signal. In one implementation, the background value is adjusted by comparing the peak value to the background value. When the peak value is greater than the background value, the background value is increased at a relatively slow attack rate. When the peak value is less than the background value, the background value is decreased at a relatively slow decay rate. The background noise detector thus varies the background value relatively slowly in response to changes in the peak value. A comparator is further provided to determine whether the peak value exceeds a predetermined threshold value. In one implementation, the predetermined threshold value is obtained through a table lookup function wherein the background value is used as an index to index into a lookup table including a plurality of corresponding threshold values. If the peak value exceeds the threshold value, a one-shot timer is triggered to activate a microphone signal path. In one implementation, hysteresis is further provided to lessen the threshold required to retrigger the one shot timer while it is active. The functionality of the peak detector, background noise detector, and one shot timer may be implemented by software code executed within a microcontroller.

A multichannel source activity detection system, e.g., a voice activity detection (VAD) system, and method that exploits spatial localization of a target audio source is provided. The method includes the steps of receiving a mixed sound signal by at least two microphones; Fast Fourier transforming each received mixed sound signal into the frequency domain; filtering the transformed signals to output a signal corresponding to a spatial signature of a source; summing an absolute value squared of the filtered signal over a predetermined range of frequencies; and comparing the sum to a threshold to determine if a voice is present. Additionally, the filtering step includes multiplying the transformed signals by an inverse of a noise spectral power matrix, a vector of channel transfer function ratios, and a source signal spectral power.

System and method for automatically measuring and monitoring the quality of acoustic data is disclosed. The system also provides suggestions for corrective actions to the system or user. The method monitors the quality of data and provides feedback to the system or user for corrective actions. The quality of data includes a combination of either a signal clipping detector, a microphone ON/OFF detector, an air puff detector, and a low signal-to-noise ratio detector.

A method of initializing an ITU Recommendation G.729 Annex B compliant voice activity detection (VAD) device is disclosed, having the steps of (1) determining a first set of running average background noise characteristics in accordance with Recommendation G.729B; (2) determining a second set of running average background noise characteristics; and (3) substituting the second set of running average background noise characteristics for the first set when a specific event occurs. The specific event is a divergence between the first and second sets of running average background noise characteristics.