The fundamental concept behind half speed mastering is bandwidth. Normally with most things the faster the better. 15ips is better than 7.5ips, 30 ips is better than 15. 45 is better than 33. 78 is better than 45.
Why? Because the information can only be laid down so fast, and so the faster the medium the greater the information density per unit time. It is spread out over a greater amount of medium (tape or vinyl) but the same amount of time.
Sorry if that is too technical. What happens with cutting is the same only different. Instead of going faster you go slower. The cutter head only has so much power to cut the dynamic swings into the vinyl. The slower you go the more time it has, and this has the effect of increasing the cutter head effective power. Very simply, it allows the cutter head to cut much more precisely the input signal.
This is totally a huge advantage. But notice, this is only one small item on a very long chain of events in making a really good sounding record. All things being equal, half speed mastering is better. But all things seldom are equal.
I have on my shelf 4 different copies of Fleetwood Mac Rumours: one original vintage vinyl, one Nautilus half speed mastered "audiophile" pressing, one 45RPM audiophile reissue, and one White Hot Stamper.
The worst one of them all is the Nautilus half speed mastered "audiophile"! Not even close. Why? Not because half speed mastered! It was "digitally remastered".
The 45 sounds great, but the White Hot Stamper sounds so much better than the 45 you can hardly believe it. Even though if you had both of them right here in your hands, my original vintage copy and the White Hot Stamper, you could not for your life tell them apart. They are absolutely identical. Yes hot wax people, even the hot wax. So forget that one.
The point is not to promote Better-records.com, but to get the point across that many, many different factors go into producing a terrific sounding pressing. No one can say buy the half speed mastered it will be better. No one can say buy the vintage, or the 45, or whatever other "audiophile reissue" fantasy story they want to pull over on you.
(If you want to be assured of the absolute highest sound quality, then you do want the White Hot Stamper. That much we definitely can say for sure.)
The one you have, BIA45, is one fantastic sounding LP. IF and ONLY IF you get one that is! Because, depending on the pressing run it can also be one of the WORST! One copy I got had dips and skips and freaking pieces of paper melted right into the vinyl. The next copy played almost perfectly.
Suffice to say vinyl is a fickle filly. As Sting would say, "That’s my baby, she can be all four seasons in one day!"