The system comprises a Digital Signal Processing module, a Power Supply Unit and an audio amplifier. In the Digital Signal Processing module, the level of the digital audio signal is detected for adjusting the rail voltage in the amplifier. The digital audio signal is delayed by the Digital Signal Processing module prior to transforming and feeding it into the audio amplifier for amplification in order to stabilize the rail voltage after adjustment of the rail voltage to an increased level. Further in order to decrease the power consumption, especially in battery driven amplifiers, an adjustment of the rail voltage to a reduced level is delayed by a second predetermined time length (S_Hold) of 1 to 5 seconds as this reduces the number of adjustments of the rail voltage.