Call Progress Tones (CPT) Generator
Call progress tones are audible tones sent from the PSTN or a PBX to calling parties to indicate the status of phone calls.  Equipment such as fax machines and modems are designed to recognize dial tones and busy tones.  The ITU-T E.180 and E.182 recommendations define the technical characteristics and intended usage of some of these tones.

Unicoi’s Call Progress Tones Generator is an integral part of Unicoi’s Voice Gateway and, in conjunction with the DMTF tone generation, is used to generate the tones to be sent to the terminal equipment. CPT detectors are used in terminal equipment for machine recognition of tones.

Discontinuous Transmission (DTX)
Unicoi’s Discontinuous Transmission (DTX), CNG and VAD are used to reduce the transmission rate during inactive speech periods while maintaining an acceptable level of output quality. VAD classifies the input signal into active speech, inactive speech or background noise. Based on the VAD decisions, DTX inserts Silence Insertion Descriptor (SID) frames during the silence intervals. During silence, SID's are periodically sent to the CNG module, which generates ambient noise during periods of inactive speech on the receive side.

Dual-Tone Multi-Frequency (DTMF) Detector
Unicoi’s Dual-Tone Multi-Frequency (DTMF) Tone Detector algorithm conforms to CCITT standards Q.23 and Q.24, and provides PSTN-like operation and performance.  The DTMF algorithm determines the single generated digit by extracting the two frequencies from the input signal, allowing for tolerances such as frequency offset and distortion such as additive noise, and then checking them to see if together they qualify as one of the digits.

Dual-Tone Multi-Frequency (DTMF) Tone Generator
Unicoi’s Dual-Tone Multi-Frequency (DTMF) Tone Generator software is an implementation of a DTMF generator and decoder. DTMF is an international signaling standard for touch-tone telephones. Fusion DTMF generator generates standard telephone digits as the sum of two sinusoids corresponding to a frequency table for each digit. The DTMF decoder will take a digital signal as input and produce the decoded digit. Fusion DTMF software generates and decodes 8 KHz PCM samples.