The application describes a microprocessor (140) adapted to receive and process digitized signals derived from an analogue ECG signal (110), said digitized signals being a digital ECG signal (133) and digital in-phase and quadrature phase band power signals (131, 132), the microprocessor comprising: a beat detection unit (141) adapted to receive the in-phase and quadrature phase band power signals (131, 132), calculate a band power value and an adaptive threshold value, and compare said band power value with said adaptive threshold value to detect a QRS complex of the ECG signal indicative of a detected valid beat (142); and an R peak detection unit (143) adapted to receive the digital ECG signal (133) and information about the detected valid beat (142), select a portion of the received ECG signal (420) as a first time window around the detected valid beat; determine the location of a first R peak position based on a continuous wavelet transform calculation of said selected portion of the received ECG signal; and perform a time domain search (480) in a second time window around said first R peak position in order to refine the location of a valid R peak position. The application also describes a system and method for analysis of ECG signals.