The ampmodem object implements an analog amplitude modulation (AM) modulator/demodulator pair. Two basic transmission schemes are available: single side-band (SSB), and double side-band (DSB). For an input message signal , the double side-band transmitted signal is where is the carrier frequency, and is the modulation index.

http://liquidsdr.org/doc/ampmodem/

The audio module in liquid provides several objects and functions for compressing, digitizing, and manipulating audio signals. This is particularly useful for encoding audio data for wireless communications. Continuously variable slope delta (CVSD) source encoding is used for data compression of audio signals.

http://liquidsdr.org/doc/cvsd/