The invention relates to a codec circuit for increasing the data transmission rate in a modem transmission. Said circuit comprises a first programmable digital filter (13) which is connected in a first transmitted signal path of the codec circuit, a second programmable digital filter (22) which is connected in a received signal path of the codec circuit and a modem signal identification unit (31) for identifying whether the transmitted signal, emitted in the transmitted signal path or whether the received signal, received in the received signal path is a modem signal. If a modem signal is identified, the modem signal identification unit (31) switches the first and second digital filters (13, 22) onto a broader filter bandwidth.