What Happens Inside the Band

A single band does not carry speech alone. The ringing tone, the busy tone, the digits pressed and the caller's number all travel through the same 300 to 3400 Hz. This volume begins with the idea of putting signalling into a path built for speech, and with the confusions that follow from it. It then explains the echo that arises where two wires meet four, from its electrical cause, and sets out what a canceller estimates and why it fails when both parties speak at once. It closes with the economy of not sending silence, and the comfort noise that economy makes necessary. Each is a different face of one subject: sharing a band.