In telecommunication, the term baseband has the following meanings:

1. The original band of frequencies produced by a transducer, such as a microphone, telegraph key, or other signal-initiating device, prior to initial modulation.

In transmission systems, the baseband signal is usually used to modulate a carrier. Demodulation re-creates the baseband signal.

Baseband describes the signal state prior to modulation, prior to multiplexing, following demultiplexing , and following demodulation.

Baseband frequencies are usually characterized by being much lower in frequency than the frequencies that result when the baseband signal is used to modulate a carrier or subcarrier.

The composite video signal created by devices such as most newer VCRs, game consoles and DVD players is a commonly used baseband signal. Broadcast or cable television, on the other hand, use a modulated signal to be able to carry many stations through a single aerial or cable.

2. In facsimile, the frequency of a signal equal in bandwidth to that between zero frequency and maximum keying frequency .