voiceband modem

A voiceband modem is a device that converts digital data signals into analog signals for transmission over telephone lines, and then converts them back to digital signals upon reception. The term "voiceband" refers to the fact that these modems operate within the frequency range typically used for human voice communication, which is a narrow bandwidth.1

Early voiceband modems, like the Bell 103 introduced in 1962, used frequency-shift keying (FSK) to transmit data at speeds up to 300 bits per second. This involved shifting between two specific frequencies to represent binary 0s and 1s. Modems have evolved significantly, with modern standards supporting much higher data rates through advanced modulation techniques like quadrature amplitude modulation (QAM) and trellis-coded modulation (TCM). These advancements allow for faster and more efficient data communication over existing telephone infrastructure.21