basisband

Basisband, or baseband, is a term used in signal processing to describe the original frequency content of a signal before it is modulated for transmission. In many languages basisband is used interchangeably with baseband. For real-valued signals the spectrum is symmetric around zero, and the energy occupies frequencies from 0 Hz up to a maximum frequency fmax, which defines the signal’s bandwidth.

A baseband signal is transmitted without shifting its spectrum to a higher carrier frequency. This makes baseband transmission common for certain media and applications, such as local-area networks using baseband Ethernet on twisted pair and traditional telephone audio channels, which carry frequencies roughly from 0 up to a few kilohertz. The baseband bandwidth equals the highest frequency component present in the signal. For digital signals, common baseband schemes include non-return-to-zero and Manchester coding, which shape the spectrum within the available low-frequency range.

Baseband signals are distinct from passband signals, which are shifted to a higher frequency range by modulation to fit a channel’s requirements or to multiplex multiple signals. In practice, a baseband signal may be converted to a passband form for transmission over wireless or long-haich networks, and then converted back at the receiver.

Key principles related to baseband include the Nyquist criterion, which states that a signal with maximum frequency fmax must be sampled at least at 2 fmax to be reconstructed without aliasing. Baseband concepts are foundational in digital communications, audio processing, and data storage.