Hi Mykle,

Yes, iFFT takes spectral-bin signals in parallel.  Right now they all
run at the full audio sampling rate, but later we should be able to
downsample as is typical.

Note that for 1/f noise there is a spectral_tilt function in
filters.lib that will provide a 1/f filter for white noise as a
special case.  More generally it can provide 1/f^alpha over the entire
audio band, for any alpha, to any desired degree of accuracy.
Moreover, alpha can be safely modulated over time as that only moves
the zeros of the filter.

- Julius


On Fri, Feb 23, 2018 at 7:55 AM, Mykle Hansen <my...@mykle.com> wrote:
>
>> On Feb 22, 2018, at 10:23 AM, Oleg Nesterov <o...@redhat.com> wrote:
>>
>> On 02/22, Mykle Hansen wrote:
>>>
>>> My latest problem: my Faust program seems to hang the compiler,
>>> locking up one CPU on my system until I terminate it.
>> ...
>>
>>> betanoise(beta) = real, imag : an.ifft(N) : select2(0)
>>> with {
>>>  N=8192; // 2^13
>>
>> Well, an.ifft(8192) needs some time to compile ;)
>
> Aha.  Or rather, d’oh.
>
>> but it seems that you do not really understand what it does. You can't use N 
>> > 1,
>> inputs(an.ifft(N)) == 2 * N and it must be equal to 2 == outputs(real, imag).
>
> You’re right, I sure don’t. =) I thought N was an evaluation window
> size, or something.
>
> I was just experimenting with Bourke’s approach, which I
> get in theory but not in practice.  The signal his code is
> feeding to fft(-1) is a complex waveform with exponentially decreasing
> magnitude over time (dithered with noise) & random phase.
> He runs it through IFFT to convert that into 1/f noise, with
> exponentially decreasing power over frequency.
>
> Peering at analyzers.lib a little deeper now …
> am I right that N is the number of evaluation
> bins, i.e. as would be produced by a forward FFT
> analysis of a signal?  (So 32 would be plenty for audio,
> and that compiles quickly enough.)
>
> If so, I guess my whole approach is 90 degrees off —
> the magnitudes need to be fed in parallel to ifft(),
> not in series.
>
> Does that seem right?  I admit I’ve never done an IFFT before. =)
>
> -mykle-
>
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> Faudiostream-users mailing list
> Faudiostream-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/faudiostream-users



-- 
Julius O. Smith III <j...@ccrma.stanford.edu>
Professor of Music and, by courtesy, Electrical Engineering
CCRMA, Stanford University
http://ccrma.stanford.edu/~jos/

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Faudiostream-users mailing list
Faudiostream-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/faudiostream-users

Reply via email to