Hello PF. Thanks for reading. My understanding of Bandwidth in the context in which I learn it (Analogue and Digital Communications) is that it is the spectral width of a signal, BW = f[upper] - f[lower]. However, my lecture notes then define 'fundamental limitations' as, Bandwidth: - A measure of "speed" - When a signal changes rapidly with time, the frequency content (or spectrum) extends over a wide range; i.e. has "large bandwidth" - The faster data is sent, the more bandwidth it uses (is needed) This confuses me. I don't get how bandwidth is a measure of speed, other than how frequency in general relates to signals in the time domain. Are the bullet points above factually correct? How rapidly a signal changes with time only determines at which frequency(s) it lies, not the width of the range of frequencies? I understand how sending data faster could require more bandwidth; by increasing bandwidth, more simultaneous signals could be sent. But to say that increasing the speed of transmission will result in an increase in bandwidth, I just don't understand that. Insight is most welcome. Thanks!