Abstract: ASCII characters are coded in the form of 8, 16 or longer digital words. Signal pulses with durations proportional to such digital words are generated and filtered so that the filtered signal has substantially the same duration as the unfiltered signal. The filtered signal fits within the voiceband so that it can be transmitted through a voiceband medium such as a telephone network. At the receiver, zero-crossings of the received signal are detected and from the duration between consecutive zero-crossings, the particular ASCII represented by the duration of such signal may be recovered.