The lecture continues...
AArrgghh! Insomnia I hate it!
PRAT is a tricky one to get a handle on.
Music/sound operates in three main areas, these being variable frequency (pitch) variable intensity (volume) and finally TIME.
If any of these three elements is missing or skewed (off key, lacking dynamics or out of synch) then things simply don't work that well.
PRAT as a HiFi attribute is all about timing.
Umm, how can I explain this...? There are heaps of drummers in the world, however if you've ever listened to, for example "60 Ways to Leave Your Lover" by Paul Simon, you may understand why there's only one Steve Gadd.
That said, on a system that doesn't have good PRAT, he may sound just the same as every other drummer.
With the right recording, a system that "times" well, should make it impossible for you not to be tapping your fingers or foot, bobbing your head along with the music, even wanting to get up out of your chair and do a shuffle around the room. Some people refer to this attribute as "boogie factor".
What gives a system good PRAT/boogie factor is tricky to pin down. Broadly speaking there will be less phase shift across the musical spectrum meaning that the leading edge of a sound be it high in frequency such as a snare or hi hat, or low in frequency like a kick drum or walking bass line arrive at the same time, rather than the bass stuff being slightly delayed. Additionally, the system will have less overhang, that is, once the signal ceases, sound levels should fall away quickly.
Beyond this, for some reason turntables seem to have better PRAT than CD/DVD/MP3 players, I might even go so far as to say that direct drive or idler drive tables (Technics SL1200, Garrard 401, Thorens TD125) have better PRAT than belt drive tables and that unipivot tonearms (in my limited experience) have better PRAT than bearing tonearms.
I have a close friend with a very well sorted Michell Orbe turntable and Rega 9 tonearm and I'd suggest that my crusty Technics SL120 with Decca International unipivot arm "times" better. You could probably buy his TT alone and the same money would net you a brand new Yeti 303 frame and a set of Boxxer World Cups.
Amps with better PRAT (huh, an amplifier can have timing???) seem to have less complex circuitry in the power supply, fewer gain stages and less (if any) global negative feedback. A two gain stage triode class A valve amp with a fast recovery power supply and zero global negative feedback with minimal capacitors in the signal path can be an amazing thing if you can tolerate the low efficiency and limited power output inherent in such a beast.
In all this, you must be aware that in audio, as with bikes, the law of diminishing returns for dollars spent kicks in wth a very big stick. Unless you are exceptionally lucky, you can pour tens of thousands of dollars into a system and reap little improvement, or you may go forward in one aspect at the expense of others.
(some early mono jazz recordings for instance, obviously have zero stereo imaging but clearly surpass the same era stereo pressings or any subsequent digital releases of the same recording for tonal accuracy, relaism and timing)
Ah well, I'm off to try and sleep again.
Drew
