Sorry but it is not bullshit...
It is.
Only m5 and Gallardo do sound "good" (and very few other) but they are still sounding artificial especially when you change gear.
Most of GT5 car engines are low rpm sample pitched to reach those max rpm instead of recording whole range of RPM. Few premium cars use even same samples as GT4 cars just remastered.
As mentioned lack of transmission sound upon gear change, lack of road sound beside standard "noise", if you hit bump in road you hardly hear it. Complete lack of car body sound under stress. lack of proper intake sound.
And no. Shit sound in 8.1 PCM is still shit sound. Sound recorded via cam in GT5 should sound like in real life according to your theory. But it doesn't because it is shit and lack ton of things.
What GT5 does good is multichannel mixing so you will hear for example properly doppler effect. BUT IT DOESN'T make shit sound better.
Kaz himself said this is problem because PS3 has small memory pool and they hope they will patch it in GT6 or it will be in GT7.
My opinion ? Don't expect new sounds in GT6
And stop using "in real life" comparison because i drive cars daily and anyone here driving car can pretty much sum it up as "bullshit"
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They also need to improve damage model. Or at least introduce it properly ingame instead of being option.