Griffith, i'm genuinely curious. How are you so confident in that PD is developing a new groundbreaking method of sound synthesis? Are you getting inside scoop or is it strictly guessing based on what you hear? You are very confident that when the update drops, it will revolutionize the sounds in GT. How can you be so sure?
Note that this is not meant to be an antagonizing post. I'm generally curious and I seriously hope you are right!
The X-cars are genuinely using a new synthesis method, anybody who's driven them would agree - I think I can say that is a given now. What's important is how that will translate to all the other cars.
Kaz said they're going to generate sounds in a completely different way. The rest is sort of long winded, but based on things like sound guys being credited for simulation work and the way the sound engine seems to have been designed (directional sources, transmission delay, frequency dependent attenuation, i.e. low pass filtering, etc.), and the attention to detail its received (since the first outing on PS3), it seems that PD are taking a certain mentality towards sound in general.
Combine that with my personal experimentation with sound synthesis, a little bit of covert nodding from PD towards potential industry partners (when talking about the LFA's sound before GT5 arrived) and my hands-on with the cars in question, I am confident that they are using a specific technique, at least as one component of their new sound. Which technique, I won't say, but anyone in the field would be able to recognise it once they got their ears around it (it's just a case of how long it takes other devs to pick up on that - I think PD have earned a short spell of upper-handedness here).
Just the use of that one technique alone is a giant leap in sound quality, in terms of expressiveness that can be achieved (if you use it right, which, arguably, the X-cars don't quite, but there might be reasons for that at this stage). It's not an increase in the fidelity of, say, a static engine note, which is easy if you have a recording (that fidelity may even go down with the new system, but engines are never stationary), rather how that sound changes with driver and physics inputs. The "traditional" method is to blend and pitch samples, which just sounds awful to me now I've heard some alternatives.
As for just how "revolutionary" the sounds will be, that'll depend on the first step of their generation method (which I have no idea about). I have a system, that is pretty lo-fi (I can't code, so I gotta use the tools available), but is, in theory, infinitely adjustable for things like cam timing, port volumes, runner lengths, fueling etc. and any differences between cylinders in any of these things (if you have access to that "info", which manufacturers will, one way or another). That interactive detail is scaleable, too - you don't have to use it all to get believable sounds.
What that means for a game is that you could potentially get into the level of sound customisation people typically undertake for real world cars, and changes from tuning parts will be accurately reflected (so your "racing exhaust" won't sound like a race car unless you upgrade the manifold, cams and intake as well, for instance). But that would require a new user interface and tuning system, so it's somewhat unlikely based on that requirement alone.
Still, infinitely expressive (fixed tuning) engine sounds with no pitching artefacts and no dead spots from blending samples (and no control quirks as with some other methods that try to sidestep those first two problems) would be a major improvement for any game, not just GT, which is so far behind expectations already.
Note: I'm not saying anyone will be blown away by it, necessarily (I think people should just expect "adequate", and see what happens) just that it represents a major step forward for the industry, finally letting go of the cheap-memory stunted legacy that samplers have given us. Where developers can take that approach to in the future is the
really exciting part.