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I'm attempting to physically model an internal combustion engine, a task much more complicated than at first imagined. I work on a lot of sync to picture material and often find that simply placing a sound effect or trying to modify a sample of an automobile is not satisfactory. I'd love to be able to control the variables involved; engine size, exhaust system, interior, exterior, doppler, etc.

I've got a pretty good idea of how to model everything after the engine, but am having trouble with how to model the exhaust impulse. There are several variables I'd like to be able to control, such as cylinder displacement, the pressure of the exhasut impule over time, the load on the engine, etc.

Problem #1. How do I modify a repeating waveform in realtime, or the "best" way of approaching this?

I've used the "GlottalPulse" waveform in a Function Generator and had somewhat satisfactory results. This waveform most closely resembles what I would assume an exhaust impules looks like on a time/amplitude graph. I would now like to vary the shape of this waveform based on the variables listed above.

Any help is greatly appreciated.

-- MichaelRadentz - 07 Feb 2005


You might have some luck with the CrossFadingMulticycleOscillator:

  1. Start by looking at samples of engine or exhaust sounds and identify individual impulses in the waveforms
  2. Copy and paste several of these impulses one after another into a single multicycle waveform
    Make each impulse 4096 samples long by selecting it and then using the Interpolate Selection template in the lower half of the Samples File Editor
  3. Use your new multicycle wavetable in the CrossFadingMulticycleOscillator? Use Index to select different impulse waveforms Use DutyCycle? or Formant to compress or expand the duration of each impulse Use Frequency to control the rate of firing of the impulses (like RPMs on the engine?) Use frequency modulation if you want to shift the phase of the impulses within a cycle

In fact, you may be able to get by with just a single impulse taken from an engine sample and using the regular Oscillator. By changing the duty cycle and repetition rate of that impulse, you should be able to emulate quite a few of the engine states you describe.

I am curious to hear what you discover!

-- CarlaScaletti - 08 Feb 2005

Question: How do I reshape a waveform based on variable imput?
Keywords: automobile waveform reshape impulse

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