Quote:
Originally Posted by Mangler
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?
T
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Yeah, this looks like the kind of app that performs analysis through the mic, which doesn't work so well for this application. When you do Fast Fourier Transforms, you're breaking a signal down in to its constituent components. Every time you reproduce the sound, you lose fidelity. This is especially true when you're playing the sound over a speaker, then re-recording it. You're suffering acoustic loss at the speaker and the mic. Add to this the fact that the mic in the iPad isn't a reference grade component, and your result is going to include all kinds of errors.
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/