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Old 18th January 2005, 07:06 AM   #31
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Quote:
Originally posted by Circlotron

Took =me= a little while to figure it out at first.

Pink for Pieces of spectrum.
Whitle for Whole spectrum.
Not quite.
Basically, white noise has equal energy per Hertz, so if you measure it with a moving filter of constant bandwidth (300Hz, 1kHz or whatever), you will measure it as flat. This is how spectrum analysers measure a signal.
Pink noise has equal energy per octave (or fractional octave), so if you measure this with a constant bandwidth filter, (like an SA), then you'll see a response that falls of at 3dB per octave. On the other hand, if you measure pink noise with an RTA, which measures in octave chunks of the spectrum (or 1/3 or 1/12th octave as required: ie, the bandwidth of the filter increases as the frequency rises), then you measure pink noise as flat.
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Old 18th January 2005, 11:00 AM   #32
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Well, the way I understand it is if I want to measure the whole spectrum in one hit e.g. 20Hz to 20,000Hz then I use white noise.
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Old 18th January 2005, 11:02 AM   #33
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But if I wanted to use an analyser that divided the spectrum of interest into bands of 1/3 octave or some other constant percentage then I would use pink noise.
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Old 18th January 2005, 11:28 AM   #34
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Your pictures show an FFT-based spectrum analyzer, which will show the same results (more or less) as a conventional filter-based SA, therefore it shows white noise as flat. You are quite correct in saying that if you used this noise as the source for an analyser that measures in 1/3rd octave bands (or whatever fraction of an octave you want to use), then it will show a 3dB per octave (or to be pedantic, a 10dB per decade) rise in response. To show a flat response on such an analyser when measuring a flat system (like a perfect amplifier, or the mythical 'straight wire with gain') then you need to use pink noise as a source.
There's nothing to stop you using wideband pink noise as a source to measure the whole 20Hz to 20kHz in one go if you have a suitable wideband pink noise source and an RTA that covers the whole band (like TrueRTA does).
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Old 18th January 2005, 12:23 PM   #35
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Quote:
Originally posted by Circlotron
Well, the way I understand it is if I want to measure the whole spectrum in one hit e.g. 20Hz to 20,000Hz then I use white noise.
hey matey, could you tell us the software you are using?

that would be of interest to some thread readers, especially if it's an affordable option...
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Old 19th January 2005, 10:45 AM   #36
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Sure!
It's CoolEdit '96.
Demo versions of it (of which you can only use two major functions at any one time) are legitimately available for download lots of places.
I love it.
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Old 19th January 2005, 11:24 AM   #37
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Quote:
Originally posted by Circlotron
Sure!
It's CoolEdit '96.
Demo versions of it (of which you can only use two major functions at any one time) are legitimately available for download lots of places.
I love it.
mmm..i'm checking out Speaker Workshop now...looks good, i'll crank it up when i get a chance...
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Old 20th January 2005, 01:29 AM   #38
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In addition to speaker workshop (but this one costs money after it expires)

http://www.audiotester.de/
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