What exactly is PRaT???

The type of music you're listening to matters in term of whether PRaT is relevant. I've listened to turntables that sound soft and somewhat indistinct rhythmically (typically high mass turntables), but their reproduction of the weight of orchestral music was stunningly good. For that music, I think pace and rhythm didn't matter much. On the other hand, jazz typically seems to benefit from equipment with some ability to reproduce pace and timing.

@yoyoyaya The Naim version of PRaT is easy to understand because it is focused on emphasizing the leading edge of notes while being harmonically lean. I've since found that the next level to PRaT involves music reproduction that has pace but is also harmonically full. Pass amplifiers fit that bill. I think @ghdprentice also mentioned that Audio Research is even better than Pass amplifiers at conveying both pace and tonal richness.

My short definition for PRaT: You can clearly hear how different voices and instruments are interacting together in music. This is particularly evident in jazz music as a vast generality.

FWIW, electrostatic speakers have PRaT in spades because of extremely lightweight of their moving elements. 

@gregm Ivor Tiefenbrun was a brilliant marketer for sure. He took the essence of British Hi-Fi and translated that into words to get awareness in the US market. I think Linn's products back in the 70s and 80s were not so different from other audio components from the UK, but the main difference was that Ivor created a "philosophy" to describe what that British Hi-Fi sound did well.

He got what many engineers miss about marketing. It's about trying to sell your strengths, not covering up all weaknesses.

@stuartk I would agree that all musical genres benefit to some level from better PRaT, but my perspective is that whether PRaT is a key element to understanding the music will vary by genre. Some musical genres like jazz have frequent quick interactions between different musicians. Better PRaT makes it easier in my experience to follow what's going on in the music. Orchestral music, as a vast generalization, tends to have interactions between the different instrumental sections that is of a nature that is not as quick and transient as those in jazz music.

@panzrwagn "Overall, I believe PRaT is fundamentally about controlling and minimizing stored energy within a system. It is the release of that stored energy that smears the sound, robbing the music of PRaT."

I think you’re right on the mark based on my listening experiences. Two categories of components that seem to inhibit PRaT from my perspective are:

1. High mass turntables
2. High powered Class AB amplifiers

Both store a good amount of energy from what I know: high mass turntables are slow to release vibration and higher power amplifiers need larger power supplies to handle the bigger current demands.

@bolong Agreed with your statement that "It requires a clean start and stop of a transient". I agree that I don't think it has anything to do with timing per se, but rather having sharp leading and trailing edges for when a sound wave starts and stops.

@audiom3 Understand the term 'sarcasm' much?

Yes, there is no such thing as PRaT in a live concert because you are listening to live instruments. PRaT refers only to the reproduction of music with a focus on how accurately the leading and trailing edges of notes or sound waves are reproduced, which may not match the original live performance.

I think precision in defining the leading and trailing edge of notes (or when a sound starts and stops) makes a difference in improving the perception of rhythm and timing. What I hear as better "PRaT" is that interactions between different instruments and voices are easier to comprehend.