An adaptive equalizer finite impulse response (FIR) filter for high-speed communication channels with modest complexity, where the filter is iteratively updated during a training sequence by a circuit performing the update: (I), where (II) is the filter vector representing the filter taps of the FIR filter, (III) is the data vector representing present and past samples of the received data x (t), d(t) is the desired data used for training, z(t) is the output of the FIR filter, µ determines the memory or window size of the adaptation, and K is a scale factor taking into account practical limitations of the communication channel, receiver, and equalizer. Furthermore, a procedure and circuit structure is provided for calibrating the scale factor K .