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      07-26-2013, 10:47 PM   #91
MCaro
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Drives: M3 & 335
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Quote:
Originally Posted by bradleyland View Post
I had similar questions, so I did some exploration of my own.

Why did you choose a hanning window?

I think he probably chose Hanning window because of the dynamic range of the audio data. Although I looked at rectangular as well, and the plot looked pretty good after I applied a lowpass filter.

Did you try a spectrogram to get better time/frequency resolution?

Spectrographs of mechanical sounds are really difficult to interpret. I've attached a screenshot of a short section if you're interested in looking at it. This is the region just before the upshift.

Have you tried running the audio through an adaptive FIR filter to remove white noise?

I'm not really sure what an adaptive FIR filter is. From what I gather, it would required input coefficients that would allow me to narrow the frequency range. I just used a lowpass filter as you can see in my full write-up.

==============

My analysis shows a result that's closer to 7400 RPM. If you download my files, you can open the .aup files with Audacity (it's free). Running spectrum analysis on the audio just before the upshift always gives me values closer to 330 Hz, not 350-360 Hz. Not sure why exactly.

Full write-up: http://upload.bradlanders.com/bimmer...ound-analysis/

Copy/paste of my Markdown source (links won't work, so you'll have to click here for the full version):



EDIT: Removed the spectrogram attachment, because it makes the thread so wide. Just download the Audacity files and have a look for yourself.

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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