> Thank you for your replies Florian, perhaps Dieter will have the
> definitive answer.

I don't know the "definitive answer" but indeed the XP filter design
generates a bit more noise than other filters (the A-107 is nothing but an
expanded XP filter). The reason is that the original signals of the four
filter stages (CEM3379 filter chip) have very low levels and have to be
amplified by about 100 to obtain the audio level used in the A-100. This
causes a higher noise floor because even the noise is amplified. And in
addition some filter types are composed from up to 4 filter stages. This
increases the noise additionally. The filter types that use only one filter
stage (i.e. 6, 12, 18, 24 dB low pass) should be a bit less noisy because
for these only one of the filter stages is used.

But with max. audio input level (i.e. just before clipping) the noise floor
should cause no problems.

Best wishes
Dieter Doepfer