From: Steve the Fiddle <stevethefiddle@gm...>  20130205 23:42:48

[snip] >> >> Nyquist frequency for all Audacity project rates (8000 to 384000 Hz). > > I'm looking in Plot Spectrum at size 256, log, Hanning window > and in that view the curve seems to be steeper for lower > frequencies (for pink as well as brown). For example at: > > 352800 Hz > amplitude 0.5, > stereo track, > 2 minutes 1 second duration > > I see 2000 Hz is 24 dB and 4000 Hz is 36 dB, so twice the > expected drop in level (unless I'm misunderstanding). > > At 44100 Hz (otherwise as above), 200 Hz is at 14 dB and > 400 Hz at 24 dB. > > You can begin to see the steeper slope at lower frequencies > even at default size 512/log. > > Although HEAD isn't correct either at low sizes/log, I don't > see the steepening of the slope there, so it's closer to 6 dB > per octave at lower frequencies. > > What is the "optimal" view to judge this in Plot Spectrum? > Set the "Size" as large as possible (16384). With a small "Size" setting there aren't enough "frequency buckets" for low frequencies and it makes the slope look much steeper than it really is. At the default size of 512 there is only one "frequency bucket" below 1000 Hz (689 Hz and the next is at 1378 Hz) so that one bucket catches everything below 1 kHz. At the largest size you'll see a reasonably accurate plot down to about 30 Hz or so and you should see that for Brownian noise at all sample rates, the slope starts to roll off at around 40 Hz so that it's just a couple of dB down from the theoretical level at 20 Hz. Although the Pink noise is optimised for 44100 Hz sample rate, that too looks good at other sample rates and I think it would be more effort than it's worth to try to optimise it further. Steve > > > Gale 