Originally Posted by taibanl
Why is the high level input, reportedly superior.
I'd be interested in the answer to this as well.
My HD600/4 has the same issues as reported above, but I've determined its an input signal issue (present even with the OE HiFi amp). The car is an E82 with HiFi + Technic harness adapter. Taking the front channels from the harness to the HD in conjunction with the low input setting (gains at min), I get noise. Switching to high voltage removes the noise but as mentioned above, it returns when the gains of the amp are turned up.
Recently I ran the front channels from the Technic harness into a Mosconi 6to8 DSP. This processor has low/high input settings as well. Interestingly, I ended up using a high voltage
input configuration to the 6to8 and retained the low voltage setting at the input of the HD. Other combinations resulted in what sounded like a really compressed signal; very poor sound quality with an unnatural dynamic range.