Progress Tones in PCM Switching Environment
S. Pitroda, R. Lindsay · IRE Transactions on Communications Systems · 1973
This correspondence defines a new set of precision tone frequencies for digitally generating normal progress tones in a PCM switching environment. The technique of generating the progress tones is similar to the one described for digital multiple frequency (MF) tone senders in which the tone is generated by reading a memory store that contains the binary words representing a presynthesized waveform [1]. New frequency combinations are derived that minimize storage requirements by taking advantage of the allowable frequency tolerances to force waveform symmetry with respect to the sampling period.