Automatic Gain Control (AGC)
Automatic gain control is an electronic system found in many types of devices. Its purpose is to control the gain of a system in order to maintain adequate performance over a range of input signal levels.

Unicoi’s Automatic Gain Control (AGC) software is designed for speech processing applications. It adaptively controls the dynamic range of a speech signal without amplifying the noise between words and phrases. It consists of two parts: voice activity detection and gain control. AGC is ideal for applications requiring consistent audio levels. 

Comfort Noise Generator (CNG)
Comfort Noise Generation is the process of creating artificial background noise to fill the silence in a voice call due to voice activity detection (VAD) or the clarity of digital communications.  VoIP communications use VAD to ignore low volume levels from the transmitting device.  Similar to the benefits of echo cancellation software, VAD reduces bandwidth consumption by eliminating transmissions when the source volume is under a certain threshold, while sending only louder sounds, such as the speaker’s voice.

CNG was developed to counter the effects of a listener receiving prolonged periods of total silence over a communications channel, including belief that the transmission was lost, choppy or difficult to understand speech, and sudden, jarring changes in sound level.  CNG effectively adds artificial “comfort” noise on the receiving end of a transmission to fill in the silent portions of a voice call.  The noise generated is at a low but audible level.

Unicoi Systems’ Comfort Noise Generator (CNG) algorithm generates comfort noise during the silence intervals, to avoid the "disconnected line" effect. Unicoi’s CNG generates noise, distributed either uniformly or shaped according to the spectral envelope coefficients, which can be passed to CNG as parameters [up to 16 Linear Predictive Coding (LPC) coefficients].


Voice Activity Detector (VAD)
Unicoi’s Voice Activity Detector (VAD) algorithm analyzes voice activity to detect silence intervals and sends silence descriptors to Unicoi’s Comfort Noise Generator (CNG) module. VAD is an important enabling technology for a variety of speech-based applications including speech recognition, speech encoding, echo cancellation and hands-free telephony. The primary function of a voice activity detector is to provide an indication of speech presence in order to facilitate speech processing as well as possibly provide delimiters for the beginning and end of a speech segment.