I had the thought to do simple db testing between the stock exhaust and RS4.
This is by no means scientific, but at the least a rough idea of actual sound and noise level difference.
Car is a 95k mile 1995 NA. 100% stock mechanically, stock intake, exhaust manifold, catalytic converter, etc. Only the Roadster Sport 4 CAT-back was was added.
The decibal meter used was Tacklife model MLM02 as found on Amazon.
Measurement distance was 8 feet from center of bumper, meter at 45° angle. Camera is a Gopro Hero 4 with Olympus external stereo mic model ME51S.
I would have edited these into a single video but my PC does not handle HD video well at all.
Also, I foolishly forgot the mic sock when recordng the stock exhaust. So wind can be heard in those, but I it doesn't affect the db meter readings.
Cold start idle:
Stock:
RS4:
Hot start idle with revving:
Stock:
RS4: