OK, looking at the OOURA code, the init routine has this:

========================

static int ooura_init( int n)

{

n = (1 << ilog2(n));

if (n < 64)

return (0);

========================

then later in the fft/ifft routine:

========================

if (!ooura_init(2*n))

return;

========================

and rfft:

========================

if (!ooura_init(n))

return;

========================

since these operate directly on samples in the signal vector, it will pass signals in small blocks without performing dft. I don't know what this is supposed to avoid. I've used fft in small block sizes before, and I can't be the only one whose patches might be broken by this.

On Fri, Oct 16, 2015 at 5:33 PM, katja <katjavetter@gmail.com> wrote:

If I understand the fft files correctly OOURA is now the default, but
'disguised' as mayer fft so the old API should remain valid.
(http://sourceforge.net/p/pure-data/pure-data/ci/master/tree/src/d_fft_fftsg.c).

Indeed I get the same result for Matt's test patch with Pd 0.46-5
which is on my system. Sinusoids for block size 8 and 16, instead of
spectrum points.

A while ago I've been reading in OOURA fft code and what I remember
is, Pd uses its mixed radix functions. Not sure about it though.

Katja

On Fri, Oct 16, 2015 at 10:00 PM, Robert Esler <robert@urbanstew.org> wrote:
>
> As far as I know Pd stopped using the mayer fft library in .46, which is probably why this is new behavior. I only get what you’re experiencing with a block size of 8. Otherwise, it seems to perform as expected.
> To really understand if this is a bug or not is to know which fft library is being used for OS X. My guess is it’s the OOURA but it’s not clear from looking at [fft~] object code that comes with distribution.
> You could also download the old library and recompile Pd, but I doubt it’s worth it.
> -Rob
> -------
> Hi list,
>
> There's either a major bug in the [fft~] objects in Pd-0.46.7 (64bit OSX)
> or I'm going crazy. I'd love to see if others can reproduce it.
>
> Basically, for [block~] sizes less than 32 bits, [fft~] doesn't perform --
> it just passes the signal through unchanged. [ifft~] does the same. The
> [rfft~]-[rifft~] is a little more complicated -- it passes signal through
> but zeroes out the last N/2 for [block~] sizes less than 64.
>
>
> See the attached patch, which only shows [fft~]. The saved contents of the
> tables on opening are the results for [block~ 8] on my machine, for
> quarter-nyquist at 44100.
>
> I've never seen this before in other versions of Pd. Anyone else get this
> behavior?
>
> Matt

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