The invention relates to a method for evaluating the quality of a signal transmission path (2) presenting non-linear distortions. According to said method a specified test signal is sent from a transmitter (1) to a receiver (3). First the level of the received signal is adjusted in the receiver (3) and then a global quality evaluation is carried out using a specified comparative method. To adjust the signal level a local quality evaluation (11) based on the specified comparative method is carried out in a specified number of different, predefined windows (V1, a, VN-1, VN). Thereafter at least one window with an adequate local transmission quality is determined. The ratio of signal level of the test signal to signal level of the received signal is calculated in at least one window and the level of the entire received signal is adjusted on the basis of this ratio. Preferably only windows containing, for example, at least 50% of the total signal energy are used for adjusting the level. The quality evaluation can be carried out using a known method such as the BSD method.