I checked a silent bit of my mono mix capture (very old recording, VHS linear track) and the RMS noise floor was about -38dB, but after correcting the DC offset it was -57dB.
A silent bit of the uncompressed ANH audio as used on my DVD (retail VHS hi fi, normalised and noise reduction applied) was about -75dB.
Tip: Use Tools -> Statistics in Sound Forge rather than scan levels in the Normalize dialogue to measure stuff.