In electronics, voiceband means the typical human hearing frequency range that is from 20 Hz to 20 kHz. In telephony, it means the frequency range normally transmitted by a telephone line, generally about 200–3600 Hz. Frequency-division multiplexing in telephony normally uses 4 kHz carrier spacing. The roll-off rate, or rate at which the amplitude of a signal drops off near the upper and lower limits can vary with the design of the band-pass filters.
The question of frequency spacing was addressed at an international meeting in the 1930s. Germany and Britain favored 2 kHz spacing, while the Netherlands and some other countries preferred 6 kHz. The question was compromised at the American position, which was the 4 kHz spacing that remained standard and also fixed the standard PCM sample rate at 8 kHz, which in turn defines what "voiceband" means for this purpose. The abandonment of in-band signaling in the late 20th century made available a larger voiceband for modems and voices.