Engine audio simulation

I’ve been searching for a few days now a way to do a vehicle engine audio. I’ve seen a lot of methods on how doing it, like changing the pitch and playback speed of the sound relative to RPM, having a set of audios with idle, and redline engine sounds with crossfading, and i came across this video:

And i found very interesting the way it was made, and i noticed this is the approach that the game Jailbreak used to make their sound engine.
And while trying the find the original file to this engine, i noticed that it was unavaliable, i tried reaching the original creator of it and i got no response.

I wanted to know how could i recreate this approach for my engine audio simulation.

How familiar are you with Fuzzy logic?

I know it’s a type of condition that uses a range of values, but i’ve never worked with it before

What makes you so certain jailbreak uses that?

I think they use a much simpeler approximation. Depending on your usecase, simple might be enough.

It uses the same Jailbreak’s engine sounds, and Jailbreak seems to have the same approach because of their engine sound crossfading

I’m by no means an expert, and haven’t used them outside of software like Labview and Matlab which does most of the heavy-lifting behind the scenes. Also, like @Apenz1 said, I doubt you’d need to use a proper Fuzzy controller to produce something like this when you can simply “hard-code” it using ratios of rpm range and limits.

To give a brief explanation, you were along the right lines with “uses a range of values”. Fuzzy logic takes a ‘boolean’ type comparison (e.g. Hot, or Warm, or Cold) and converts it to a ratio-type comparison (e.g. 60% Cold, 40% Warm) which can be more representative of the actual thing you’re trying to represent. To use the same example:

You can then apply ‘generic’ rules, such as:

  1. If “Hot”, turn on A/C, turn off Heating
  2. If “Warm”, turn off A/C, turn off Heating
  3. If “Cold”, turn off A/C, turn on Heating

Then after the logic determines the ratios, it might then (based on our previous example), turn off the A/C and turn the Heating on to ~40% (as a guess).

From my understanding, it’s basically a means of producing a representative output based on a set of varying inputs. In your example, they’re (presumably) taking inputs of RPM and load, and using rules such as: "If RPM < 2000 AND load < 10000, Play ‘Idle’ "

Once the Fuzzy logic takes into account the weightings of all of the rules, it will produce variables that can then be applied to pitch/volume of each audio.

I’m not sure if there are any open-source lua libraries that you could utilise, and either way I’d probably just recommend considering each audio file and writing your own methods for each individually, such as:

local function getRatio(value, min, max)
    value = math.clamp(value, min, max); -- Clamps the value so you don't accidentally get ratios <0 or >1
    return (value - min) / (max - min);
end

local rpm = 1250; -- Example value within the range
local IdleStartPitch = 0.7; -- "minimum" pitch of the Idle sound
local MaximumIdleSoundIncrease = 0.2; -- "maximum" amount of pitch increase for the Idle sound

if (rpm > 500 and rpm < 2000) then
    local ratio = getRatio(rpm, 500, 2000)  -- Returns 0.5 (as 1250 is half-way between 500 and 2000)
    IdleSound.Pitch = IdleStartPitch +(MaximumIdleSoundIncrease *ratio); -- Gradually increases pitch as rpm increases up to 2000
end

Thanks for the explanation and help! I will be looking towards it.

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