Q.How is the bandwidth required to transmit digital data related to its bit rate? Explain qualitatively why a higher bit rate demands a larger bandwidth.

Every kind of message signal needs a certain range of frequencies - its bandwidth - to be represented faithfully, and this determines what sort of communication system can carry it. Speech needs roughly 300 Hz-3100 Hz (about 2800 Hz of bandwidth) for commercial telephony; music needs about 20 kHz because instruments generate higher-pitched overtones than the voice does (audible sound overall spans about 20 Hz-20 kHz); picture/video needs about 4.2 MHz, so a complete television signal (video plus audio) is typically allotted 6 MHz. Digital data, sent as rectangular waves, is mathematically a sum of a fundamental sine wave plus an infinite series of harmonics at $2\nu_0, 3\nu_0, \ldots$; reprodu …