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07-26-2013, 09:04 PM | #89 |
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I bet BMW will make it 7500rpm
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07-26-2013, 09:38 PM | #90 | |
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07-26-2013, 10:47 PM | #91 | |
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Great response, I'm going to work through it when I am back on Sunday, I would like to compare possible solutions. Luckily, it should not take too long to examine it using python or MATLAB. Do you mind PMing me the audio file? |
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07-26-2013, 11:19 PM | #92 | |
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http://upload.bradlanders.com/bimmer...ound-analysis/
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07-27-2013, 12:02 AM | #93 | |
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07-27-2013, 01:10 AM | #94 |
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Probably an obvious step but for anyone playing around with this try to establish a baseline predictive capability using some dyno videos - no Doppler and a known redline.
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07-28-2013, 02:17 AM | #97 |
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We may be losing sight of some important details in our (myself included) obsession with a high redline. I sure hope that the upper ranges of the engines rpm range are both useable and required and most importantly - exciting to use.
I'm digging the bet ^ just above!...
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07-28-2013, 09:07 AM | #98 |
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I took a 1/3 octave snapshot of the highest rev point at the 3:06 point in the video. There are two peaks at 300 and 500hz but all the energy is around 1200hz and they are not harmonics. How are you deriving the 370hz for the calculations? When I am back to a PC ill post a screenshot. Don't know why we can't just upload pics from mobile. So stupid.
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07-28-2013, 02:08 PM | #99 | |
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07-28-2013, 02:18 PM | #100 | |
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1) What tool are you using to perform the FFT? 2) What windowing function and size are you using? 3) What do you mean by a 1/3 octave snapshot? Do you mean a bandpass filter; if so, what specific frequency range? Below are answers to my own questions ![]() 1) Swamp and I are both using Audacity's "Plot Spectrum" feature, so it'd be worth running it through another tool. The math should be the same, regardless of the tool though. 2) I've tried Hanning (preferred), Hamming, and Rectangular at 512 window size. All produced highest amplitude peaks at 320 Hz - 330 Hz 3) I applied a lowpass filter, but it's completely unnecessary for the FFT analysis because of the windowing function. It just eliminates noise, where "noise" is defined as anything that falls outside what could reasonably be assumed to be the primary cylinder firing impulse. In general, I don't see much amplitude at all in the 1200hz range when using rectangular/hamming/hanning windows at a window size of 512. How are you extracting audio from the video? I used a tool called AudioHijack to capture system audio internally, but a better method would be to download the video data, then extract the audio stream.
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07-28-2013, 04:22 PM | #101 | |
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If you're interested in the code, it is as follows: Code:
clear; clc; close all; % Read the file in in [clip, fs] = wavread('m3clip.wav'); % Shorten the clip and only select one channel clip = clip(4*fs:fs*(4.3),1); % Have a listen to make sure it is okay soundsc(clip , fs) % Display the length of the clip disp(sprintf('The length of the clip is %1.2f s',length(clip)/fs)) % Apply a hamming window clip = hamming(length(clip)).*clip; % Create a linearly space independent time vector t=linspace(0,length(clip)/fs,length(clip)); % Find the coefficients for a lowpass butterworth filter [B,A] = butter(5,600/(fs/2),'low'); % Filter the signal clip = filter(B,A,clip); % Find the coefficients for a highpass butterworth filter [B,A] = butter(5,200/(fs/2),'high'); % Filter the signal clip = filter(B,A,clip); % Pad the signal with zeroes to increase the FFT's efficiency nfft = 2^nextpow2(length(clip)); Pxx = abs(fft(clip,nfft)).^2/length(clip)/fs; % Create a single-sided spectrum Hpsd = dspdata.msspectrum(Pxx(1:length(Pxx)/2),'Fs',fs); plot(Hpsd); title('Power Spectral Density for the F80 M3 Sound Analysis Thread') Last edited by MCaro; 07-28-2013 at 05:40 PM.. Reason: forgot to window the signal |
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07-29-2013, 09:33 AM | #102 |
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Here is the RTA snapshot that I took with an RTA tool on the iPad. Not nearly the level of analysis you guys are capable of. This was taken at 3:04 in the video clip where the engine noise is the loudest passing by. Not scientific at all just interesting that there is a peak at the frequencies that you center on and then the bulk of the energy is much higher. How are you selecting the frequency that you are?
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07-29-2013, 01:06 PM | #103 | |
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How are you selecting the frequency that you are? The RTA app you're using takes an audio sample, performs Fast Fourier Transforms, then creates a histogram of the amplitude and frequencies derived from the source material. The tools we're using allow us to import the actual source file (audio extracted digitally from the video), so there is no reproduction error, and we can operate on the full range of frequencies present in the source audio. Granted, there's some loss in the compression that occurs when the video is rendered, but from there, it's digital reproduction, so the operations are lossless. Download Audacity on your computer, then get the source files from the end of my write-up: http://upload.bradlanders.com/bimmer...ound-analysis/
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07-29-2013, 01:07 PM | #104 |
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The download link at the end of my write-up was broken, but I fixed it now, so you can download the full Audacity source files if you'd like to explore a bit.
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07-29-2013, 02:14 PM | #105 |
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You CANNOT average into 1/3rd octave or any other similar averaging techniques with this method. You need full spectral data. If you don't understand this, you probably should not be blindly throwing software at this problem...
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07-29-2013, 04:11 PM | #106 | ||
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I agree. Using software without a fundamental understanding of the material (in this case, signal processing) is a bit like trying to run before learning to walk -- don't do it. |
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07-31-2013, 01:52 AM | #107 |
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This is positive news and great job to the guys who figured it out. So 8K red line from a turbo 6 now we are talking. All it needs is a proper hydraulic steering on par with last gen 911 and keep the price hike to minimum and we might have a great car at hand.
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07-31-2013, 03:58 AM | #108 |
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@swamp2
You did a sound analysis quite easily, could do it to figure out if the engine is I6 or V6 (90°)? Also, the "spies" cannot stand anywhere around the N-Ring, so there are places where the can cannot be filmed/photgraphed. The drivers apparently where told to shortshift/not rev to max at places where spy photographs are standing. |
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07-31-2013, 11:16 AM | #110 | |
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Watch this video and post any timestamps of regions where you find that: If you do the footwork, I'm happy to do the analysis.
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