So, the X2014 Junior, then.
(Edited for betterer video I've pilfered from another thread...)
I've had a play with one on its own on the track, and did my best to figure out how the sound was being generated by ear. It's not the same old sampling scheme, that's for sure. I thought maybe it's the new-fangled granular ramp playback, like you get with the new NFS game and GTA V, among others. But the steady state sound is flawless and there is a smooth progression between on and off-throttle that is infinitely adjustable.
That leaves several possibilities, but there is a particular sound that stands out to me, and that's the "tube"-like resonance you can hear in the overall sound, but also in the aliasing under the distortion (sounds like a resonant filter, unsurprisingly). This points to a specific technique in my mind, and I don't think I was a million miles off when I was talking about Yamaha previously! It's beautifully expressive, and just what I was hoping for, assuming it doesn't just do raspy four cylinder sounds (which there's no reason to believe it does).
What's interesting is that the sound is technically wrong, and there is still only the exhaust sound. This implies it's still using the same source mixing method as for the sampling case (i.e. the same sound engine, which makes sense). The lack of intake sound is still hurting here,
compare (EDIT: and
this).
As for my claims of "wrongness", it's clearly playing the same 4-1 exhaust sound back from both exhaust locations on the car, which is causing the now-infamous phasing sound (plus lots of audible interference in the form of volume fluctuations). I'm hoping that's a limitation of the source mixing in use. The exhaust also sounds excessively long given the apparent packaging, which is an artistic issue (the "settings" are wrong on the synth, effectively).
Now, it seems the sound engine can dynamically allocate and switch between streams, which effectively allows PD to have many more of them "registered" in the scene and only select the maximum number the hardware can handle to "audition" at any one time (basically a level of detail system).
Add to that the fact that many people have been having problems with sounds dropping out or not even coming in at all (it happened to me once for about a second), I'd say what's holding PD back at the moment is being able to have all the sources they need for every car in the scene, and have the sound engine robustly switch between them all without audible drops or total failures.
What I don't understand, though, is why they didn't use the new exhaust sounds for all cars.
Still, I can't wait for them to get them working.