Modem receiving from/transmitting to a DTE data bits at a rate DR and adapted for operating at a modulation rate MR in an environment operating at a basic rate BR. In the receiving way, it comprises a first means for converting a number X of samples received at a frequency FS into a number X times MR/BR of samples before processing these samples by the signal processor whereby the processing results in DR/BR words of DR/MR bits, and second means for converting the DR/BR words into DR/MR words of DR/BR bits to be transmitted to the DTE. For the transmitting way the first and second converting means, are the same means but run in the reverse order. The result is that such an adapted modem behaves as a modem operating at a modulation rate MR on a periodic process interval of DR/(BR times MR) seconds.