>>They give you the opportunity to even model the sound based on the
>>layout of the muffler. But it sound verrrry synthetic.
> Interesting. I think it would be pretty simple to include a basic muffler
> model (at least a vibrating muffler anyway). I wonder how that would sound.
> This isn't a 3D system though like the gti software most likely is, so it's
> interesting that you find it sounding better even though it's far simpler,
> probably.
But it might be more accurate for engineering... I haven't got the
opportunity to compare with an engine that corresponds to the model.
I've noticed a difference in approach between "*** industry" and
engineering.
Ok, I'm thinking in a very different way... Since I am working with
dynamic systems every day it is natural for me to formulate everything
as large models an then trying to simplify them using different
model reduction methods. My idea was to simulate the engine as a
simple system and just coupling the sound directly to the engine RPM.
The engine dynamics would then be incorporated in the simulation of the
engine as a whole.
88 kHz might be a bit high for physical simulations... But it might be
possible to approximate the pressure variation in the cylinder using a
cosine function, or even a quadratic function like x^2. I've already
tried to play a sequence of synthesized pressures two years ago, but it
didn't sound very good. Sounded much like playing abs(cos(x)).
I think you should go for the full model and then simplify it by trying
to get a grip of which components that matter.
Yep... It's like numerical integration, but more general. If you
formulate a linear continous differential system you can discretize it
by e.g. first Laplace transform it and the apply a discretization
transform into the Z-transform. Yes, I know it sounds horrible, but it
is actually quite simple once you understand the what's behind the
nomenclature.
By "recursive" I don't mean recursive in code, but in the algorithm...
Like: y(k+1) = a0 * y(k) + a1 * y(k-1) + a2 * y(k-2) + ...,
which will be calculated once for every iteration.
It will depend on old values which already has been calculated which
makes it efficent. The coefficients a0, a1, ... can be dependent of
different states in the engine, like RPM, pressure an so forth...
My point is that if you first formulate the physical system as a large
system of differential equations (which is the hardest part) it is then
quite simple to reduce it all into a couple of cryptic recursive
equations as the one above that has to be calculated often enough. :)
There are many known powerful methods for doing this.
Hmm... I made a quick search in the SAE Digital Library and found:
SAE 2000-25-0255, Interactive vehicle interior sound simulation.
SAE 1999-01-1809, A sound simulation technique used for the predicition
of passenger compartment noise.
SAE 968054 , Simulation and sound quality evaluation of car
interior noise for JARI driving simulator.
SAE 951755 , Numerical simulation of exhaust flows and tailpipe
noise of a small single-cylinder diesel engine.
etc. etc...
There seems to be a lot of literature on this subject. It appears
that most of the simulation techniques are based on simulation of
the flow of gas in the pipes. 1-D models seems to be sufficient.
Some even includes Helmholtz resonance simulation (resonances in
the intake pipes due to valve opening and closing if I remember
right).
Well, this do seem as a really interesting subject indeed! But I have
to get back to work now. :(
--
/S
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