The width of the track plays a huge role in tape noise, as well as the skill of the recordist at "gain riding". If we look at a cassette tape, moving at 1 7/8IPS, the width of each track is slightly less then 1/32". My half track RTR uses 1/4" tape, but only has 2 channels, so the track width is slightly less the 1/8".
More magnetic particles, the more the field strength. My Revox does not have any Dolby, but has produced very quiet recordings.
If your machine has Dolby (or a dbx) circuit, then hopefully, you will also have panel access to bias control, because such noise reduction circuits will alter the bias for each type of tape formulation.
Wayner