Pulse Code Modulation: A technique for converting analog signals into digital form that is widely used by the telephone companies in their T1 circuits. Every minute of the day, millions of telephone conversations, as well as data transmissions via modem, are converted into digital via PCM for transport over high-speed intercity trunks. In North America and Japan, PCM samples the analog waves 8,000 times per second and converts each sample into an 8-bit number, resulting in a 64 Kbps data stream (a single DS0 channel). The sampling rate is twice the 4KHz bandwidth required for a toll-quality conversation.