Love the graphics in PC but definitely think the sound needs much more attention and is not on par with the visual aspects of the game. Ok, so what am I talking about?
1) The rate at which the audio sample rate is modulated is not high enough. How does this translate? Glitchy, unnatural engine noise when revs go up/down very quickly. Slower rev changes wouldn't be noticed but rev the engine when stationary and it's obvious that it's a computer. Higher rate would solve this, at a slight cost to CPU - could easily be implemented and made optional for high res audio. Guessing this is the mix rate of the sound output.
2) When speccing other players the noise of the engine is really messy, guessing this is a net code issue...
3) Environmental effects - racing down the straight at Spa for example, should create a cacophony of noise from the right-hand side as you scream past the wall..
4) Option to mix (by %) the engine sound you normally hear only when viewing the car externally, from within the cockpit. Let's face it, no one uses that view and it's the only way to hear the car properly. On open top cars, this should be a default % already.
5) Better flywheel simulation. It's not loud or realistic enough
6) Where are the squeaks, rattles, creaking? Especially with older cars. GTR has this bit sorted.
7) Other cars just seem to sound loud enough. An Aston Martin V12 doesn't so much scream past you, but kind of remotely buzz....
8) Wind noise, again, it's just not enough, especially on open top cars.
9) Off-throttle backfires. Only audible when viewing externally most, if not all, of the time....especially on turbo cars.