Originally posted by Roger Memphis
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Originally posted by geoffbrown
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I spent some time building a white noise generator, but never got one working whose noise was white enough (they all generated blue noise). Finally, I just gave in, generated a 60 second white noise .wav file, and used my phone as a test signal generator (can't use .mp3 for this, as it messes up the spectrum). I built a couple of custom cables that plugged into the phone, terminated with either an RCA plug for line-in, or alligator clips for "A" and "B" in.
To measure the response, I fed the output (via a line-out that I'd built into the organ long ago) into the input of my laptop, running Audacity to record the 60 second long noise burst, and generate the spectrum. I exported the spectrum data to .txt files, and imported those into a custom program I wrote that generates the graphs you see. The program can compute the difference between two spectra (that's how I generated the "relative effect" graphs), and for the non-difference graphs, I actually generated the difference between the measured signal and the raw signal to adjust for any non-flatness in the noise. That's one advantage to using a recording of white noise; it's identical every time.
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