This paper examines the common properties of modulation methods that use orthogonal basis functions, including single carrier (e.g., 64-QAM or 64-state quadrature amplitude modulation), multi-carrier (e.g.,OFDM (orthogonal frequency division multiplex)), and spread spectrum. It also explains a time frequency swapping technique that reveals OFDM and single carrier modulation are duals of one another, if the time axis and frequency axis are relabeled. This time-frequency swapping technique allows new modulation candidates to be created, such as duobinary (partial response signaling) OFDM, which has valuable properties for the cable plant.