I see these as:
1. Burble is that lovely V6 'wobbly' noise in my opinion, best heard in the lower rpm range.
2. Crackle would be a form of bang on overun, though I would say crackles, pops and bangs all sound different and easier to show irl.
3. Roar is when full throttle, the car comes to life and is shouting.
4. Rasp is, debatably, that horrid lack of tone and 'wasp nest' sort of noise. Eg. A loud civic is often raspy af. 350z's suffer from it when you dont have many resonators/mufflers etc. A straight pipe would be a lot more raspy than say an ark grip
Thats my interpretation of them anyway!
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