BASEBAND

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 . Note 1: In transmission systems, the baseband signal is usually used to modulate a carrier . Note 2: Demodulation re-creates the baseband signal. Note 3: Baseband describes the signal state prior to modulation, prior to multiplexing , following demultiplexing , and following demodulation. ( 188 ) Note 4: 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 . 2. In facsimile , the frequency of a signal equal in bandwidth to that between zero frequency and maximum keying frequency . ( 188 )