spandsp: The V.27ter receiver

spandsp 0.0.6

The V.27ter receiver

# What does it do?

The V.27ter receiver implements the receive side of a V.27ter modem. This can operate at data rates of 4800 and 2400 bits/s. The audio input is a stream of 16 bit samples, at 8000 samples/second. The transmit and receive side of V.27ter modems operate independantly. V.27ter is mostly used for FAX transmission, where it provides the standard 4800 bits/s rate (the 2400 bits/s mode is not used for FAX).

# How does it work?

V.27ter defines two modes of operation. One uses 8-PSK at 1600 baud, giving 4800bps. The other uses 4-PSK at 1200 baud, giving 2400bps. A training sequence is specified at the start of transmission, which makes the design of a V.27ter receiver relatively straightforward.