cyrille henry cyrille.henry at la-kitchen.fr
Mon Jun 16 12:22:56 CEST 2008

```hello,

Charles Henry a écrit :
> On Tue, Jun 10, 2008 at 10:29 AM, cyrille henry
> <cyrille.henry at la-kitchen.fr> wrote:
>
...

>
> I'm having trouble compiling, due to the garray_getfloatwords symbol.
> Which version of Pd are you using?
vanilia 0.41.4

>
> I'd like to see the waveform and test it out.  Here's my analysis of key points
>
> (a=x[-1], b=x[0], c=x[1], d=x[2])
>
>    83   	a0 = d - c - a + b;
>    84 		a1 = a - b - a0;
>    85 		a2 = c - a;
>    86 		*out++ = ((a0*frac+a1)*frac+a2)*frac+b;
>
> At frac=0, output should be b.  Check!
>
> At frac=1, output should be c
>
> ((a0*1+a1)*1+a2)*1+b
> =a0+a1+a2+b
> =d-c-a+b  +  a-b-(d-c-a+b)  +  c-a  +  b
> =d-c-a+b  +  a-b-d+c+a-b  +  c-a +  b
> =d-c-a+b  +  2a-2b+c-d  +  c-a  +  b
> =c
>
> Check!
>
> 1st derivatives:
>
> At frac=0,
> d/dx f(x) = c-a
>
> (This quantity really ought to be (c-a)/2, but let's see how the rest comes out)
>
> At frac=1,
>
> d/dx f(x) = 3*(d-c-a+b) + 2*(a-b-d+c+a-b) + c-a
> =d-b
>
> So, we've got 1st derivatives that match between samples.  Check!
>
> This looks like a really good plan.  I might suggest some new
> coefficients to try:
>
> a0=(3b-a-3c+d)/2
> a1=a-5b/2+2c-d/2
> a2=(c-a)/2

ok, i don't have time for now to test anything.
i'll have more time in 1 or 2 weeks.

>
> The only difference is the 1st derivatives are (c-a)/2 and (d-b)/2,
> respectively.
>
> Maybe you could try a 5th-degree polynomial next and set the 2nd
> derivatives for continuity.  This would involve 4-points as before,
> but it might introduce a ripple in the interpolation (cubic
> interpolation can't do that, since it only has two critical points).

i tried a Hermite interpolation.
it sound great, but i did not had time yet to explore the tension parametter.

here is the code if you wish to explore it.

>
> I'm not keen on doing the spectral analysis, because it would take
> about 4 hours, to do it by hand.
>
> There's something I would like to see (once I can compile it).  I made
> a patch (attached) a while back to view the tabread4~ interpolation
> function (impulse response).  Give it a try if you're inclined to do
> so, because it might surprise you.

attachement is a pict of the impulse response of tabread4~ and tabread4c~.

cyrille

>
> Chuck
>
>>
>> cyrille
>>
>>
>>> Chuck
>>>
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