I dont hear any differences with set system in High output from my HU on music, above 3volts (gain amp 15-20%) and normally set from play BT/AUX output about 0,5volt from aux, and about 1 volt from USB (GAIN AMP set 55%) No diferences, Norrmally? Alpince cde 178btCheap, low voltage on the out puts are suspect in my book.