A multi-bit digitizer (30) for a barcode reader detects the presence of edges of a scanned barcode symbol, and also measures the strength of each detected edge. A polarity or edge direction signal (8) indicates the direction of each detected edge, and a timing signal (6) is representative of the timing and also, by means of a variable pulse width, the strength of each edge. A gating signal (200) indicates that the data are unreliable and invalid if the measured voltage applied to the scanner motor of the barcode reader is higher or lower than defined limit values. Any scans made at a speed which were too high or too low are rejected.