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07-31-2013, 11:22 AM | #111 | |
TIM YOYO
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http://craig.backfire.ca/pages/autos/v8-engines#firing For a given RPM, a V8 will have a higher sound frequency, because it has more combustion events per revolution, so if you know the RPM, it's trivially easy to determine the number of cylinders through frequency analysis.
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07-31-2013, 11:27 AM | #112 | |
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07-31-2013, 12:53 PM | #113 |
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Let me ask you a question. What insight do you want to gain? I assumed you were interested in the gear spacing, but I'm not sure that's correct. I can tell you the highest amplitude frequency before and after the shift, but that will only tell you the relative difference in RPM between gears; it won't provide any insight in to maximum RPM.
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07-31-2013, 01:03 PM | #114 |
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The "illusion" you refer to is called doppler shift. It can be corrected if you know the correct inputs, but we have to guess because we don't know the velocity of the car, nor the exact angle-of-travel relative to the recording source. If you're making a relative comparison, and the inputs are close enough, you needn't correct for it.
I used the 1:30 region for analysis. Samples:
Highest amplitude peaks (not corrected for doppler, Hanning window):
Plots: ![]() ![]()
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07-31-2013, 01:53 PM | #115 | |
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07-31-2013, 03:13 PM | #116 | |
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Thanks for the frequency plot. If anyone can shed some light on speed approximation for the piece of track involved. We can at least guess a gear number. |
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07-31-2013, 03:33 PM | #117 | |
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I'm not going to guess on what the doppler effect is, as speed unknown. Assuming a gear change at say 7,000rpm, next gear is 5,600rpm. That is quite a long gear spacing if from 3-4th on a 7 speed box. ![]() Little movie I took in the M6, very similar. Forward to 27 seconds. |
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07-31-2013, 06:18 PM | #118 | |
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07-31-2013, 06:23 PM | #119 |
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Ah, in that case, I don't think waveform analysis is sufficient to identify the difference without some very specific circumstances. E.g., a V6 with dual exhaust, and a stereo mic placed on the centerline.
If you had a very detailed recording, you could examine the waveform from various examples of V6 engines versus I6 engines, but you'd need a high quality recording with many samples. Ultimately, I think there are too many confounding factors, like exhaust design and turbocharger configuration.
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08-01-2013, 06:29 AM | #120 | |
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On a parallel twin turbo straight six, although not as dramatic as the Subaru, the front 3 cylinders typically have a longer exhaust path, which phases the sound out of sync with the rear 3. This could give the impression it is a V shaped engine sound. Certainly the M3/M4 doesn't sound like a conventional inline 6. |
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08-05-2013, 12:28 AM | #122 |
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Nope, you need the sound right before a shift and a likely redline shift as well. As a side note I believe it is unlikely that the car will require redline shifts in the upper gears to extract maximum acceleration (unlike current car).
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08-05-2013, 01:53 AM | #123 | |
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08-08-2013, 08:10 AM | #125 |
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I don't know what the heck that whistling noise is, but it won't prevent a Fast Fourier Transform analysis of the engine RPM. To do that, you'd need to produce a tone similar in frequency to the primary combustion impulse. That whistle is way too high-pitched. Maybe it's a harmonic, but each multiple you move from the fundamental, the benefit of confusing the base frequency would be diminished. That whistle would have to be a shriek.
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08-08-2013, 02:05 PM | #127 |
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I strongly suspect it is just pressurized air, air/fuel or even exhaust leaking in the turbo system somewhere due to a poorly fitting part or an improperly torqued bolt(s). This is a known issue. As noted above this would not disguise the fundamental combustion frequency in a fourier transform.
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08-08-2013, 05:33 PM | #128 |
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