EDIT: Eep, 's a big un! Last paragraph is the important bit; the other stuff is just how I justify my opinions.
I record music and sound for a living. I have almost 20 years experience and own my own recording studio. When you play GT5 and compare it to other racing games you just can't help but feel the sound was almost bolted on like an afterthought. Tenacious D's comments about some of the engine sounds sounding like they are over compressed MP3's are spot on. there is just no depth to the audio. Compare the effects to other games such as Forza 4 or Shift 2 and there really is no comparison.
If you take a look at Kaz's choice of menu music the gentle Jazz piano and almost sterile pop sounds the noise of the cars engines almost fit right in, they are not "in your face" or scary. Anyone who has spent days on a real race track knows that V8's do not sound like they do in GT5, they should instil that feeling of danger and almost intimidate you with the tickover.
I love GT5 but as a sound engineer I wish I could have a crack at re-mastering those sound effects. and I would be happy to do it free of charge just to enjoy a full and proper audio driving experience
In terms of sound design, you might be right that PD favours a more understated approach. I would argue that PGR4 was the same, but that has excellent (accurate) sounds for most if not all (100 ish) cars. So it's not really anything to do with the jazz or what have you, especially with the "rock" and house type stuff that's thrown in there too (sure, no hip-hop). Add in the awesome high dynamic range of the large theatre setting and it really falls apart - that's nothing if not in your face!
It seems to me that GT sounds the way it does potentially more because of an oversight early on in the series when recording cars. Perhaps getting sounds for the 650 cars in GT2 was just too much at that time, and the hardware couldn't really do the samples the best justice anyway (only the player's car used the new samples; the opponents reverted to the GT1 method).
So along came the PS2 and its extra horsepower, the samples were now applied to all cars on track, and they included the engine sound too. But, possibly, the recordings they had didn't include intake, or the intake sound was too inaudible to be of any use (especially if free revving was used for all cars, which seems likely given the cost and relative geographic dispersion of many of the cars). So in a way, GT3 sounded at once better and worse than GT2, just in terms of engine sound.
GT4 included more cars than there had ever been, but the recording methods seemed the same as they had been for GT2, although most of the samples from GT2 were carried over anyway. That said, there are a few examples of cars that were recorded on rolling roads, perhaps only when "convenient" (Audi's R8 etc., there was even a video of a car - I think a Vector or similar - being recorded for GT2 on a dyno, too.) Some cars have better samples than others, in that they're clearer and less marred by looping artefacts and instabilities and have less "ancillary" masking, like flow noise from exhausts or belts, fans and other things on engines, with the sound of combustion seemingly radiating from the block more clearly (try the E46 M3 startup sound; that's got a prominent block noise, sounds like a tractor). In that sense, it may be possible to pinpoint those cars that were recorded on the rolling road.
That still leaves the massive gap with missing "upgrade" sounds (again, most of which I recognise from GT2, with some frankly "interesting" additions that most people seem to loathe, myself included) and, once again, missing intake. It's possible PD have intake recordings for all or some cars, but don't include it for consistency reasons (rolling road vs. free revving) so that all cars have whizzy engines, and more-or-less accurate stock exhausts.
All of this leaves us, often, with interior views dominated by the engine noise, which of course is bereft of intake sound. Guess what sound is most important in interior views, especially in stock cars?
Secondly, the modified sounds; there is little consistency: why does the '64 GTO always sound like a V8 irrespective of mods, but a C4 ZR-1 (or '00 Camaro SS, same samples) will sound like a 6-cyl as soon as it's tweaked? Add in a general scarcity of modified sounds, and we have the state that GT5's sound can be if you're not paying attention.
Of these issues, the only one I expect could be "fixed" is the consistency of accuracy of the modified sounds versus the car in question - i.e. make the ZR-1 sound like a cross-plane V8 (the samples exist!), and my beefed-up Sirion like a proper 3-cyl (any skyline loop will do!) when modified, please!
The lack of samples (intake, plus modifieds) will have to wait until PD realise what they've done and get around to re-recording what they missed. Maybe they've started already.
Hopefully the other sound effects, turbo, exhaust overrun / splosions, gearbox whine, tyres, wind etc. can all be tweaked (and retweaked, by us) too.
