Dual-tone multi-frequency (DTMF) signaling has become a widespread cost-effective method for low-volume data communication. DTMF receivers used in such applications are generally adequate if input signals are hard wired to the telephone line. However, when the signals are coupled acoustically to the telephone, standard receivers perform poorly. A previous publication examined the special problems involved in receiving acoustically coupled DTMF signals. It is shown how the principles developed in that publication can be applied to the design of a receiver optimized for acoustically coupled signals.
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