Final adjustment of amplification parameters called fine tuning is performed while presenting the user with realistic acoustical environment during operation of the hearing device. Fine tuning relates to slight changes of the parameters initially obtained by the "fitting formula". The acoustical signals are presented using audio streaming through the hearing aid. In particular the presented signals include "speech in quiet" and "speech in background noise". Presented speech signal is composed from two or more sources that are processed with different signal processing parameters. During the presentation of the speech signal App presents the speech source visually as two or more speakers. The user is asked to provide his listening preference by choosing the preferred speaker. The signal processing parameters relating to the preferred sound are used for final adjustment of hearing device.