Hi!!!
I'd have to differ with the previous opinion, (EDAN).
A 1/4" 4-track and a 1/2" 8-track should have the same overall fidelity *(AT THE SAME TAPE SPEED), with the obvious exception that the 1/4" has 4-tracks and the 1/2" has 8,... given that all other things are equal *(HEADS/ELECTRONICS), such as in a series of units like the Tascam 30-Series (32/34/38).
Without consulting the (Tascam) manual, (which I'll do later), the track width on the 1/4" 4-track should be virtually the same as the 1/2" 8-track. Also, the electronics of these (Tascam 30-Series) decks are virtually alike.
IF, by chance, you're comparing different makes and brands of recorders, then all bets are off, and they should be compared on a case-by-case basis.
F/I, a Tascam 38 won't sound quite the same as an 80-8, nor will it sound exactly the same as an Otari or Ampex recorder, although the track width & tape speed on these different decks should be virtually the same. At that point, differences in the heads and electronics will give a characteristically different sound for each deck.
So, given what you're comparing is not clearly defined, there's a lot of leeway for differing answers on general fidelity of units. I've framed my basic answer in a Tascam:Tascam comparison of formats,... but there's a lot more to it if/when you mix & match various formats and brands for comparison.
