Hi Christof,
Thanks!
Don't forget the guard point, which could also be set explicitly to 1.0
Matt
On Wed, Jun 5, 2024, 4:29 AM Christof Ressi info@christofressi.com wrote:
Hi Matt,
thanks for chiming in!
Christof:
This should ensure that the table is symmetric, unless the underlying cos() function is broken :)
I think the underlying cos() function is dependent on architecture and compiler?
Yes. cos() is a library function, so the output depends on the particular C library implementation, the compiler and the also architecture. I would still expect it to be (reasonably) symmetric, but I haven't really checked.
Even with the new cosine table, on my machine the zero crossings have a (very tiny) residual, so it's sitting at a very small DC offset.
You're right, I didn't consider the peaks and zero-crossings! The values of 1/2 PI, PI and 3/2 PI cannot be accurately represented as floating point numbers, so the result of cos() may be a bit off.
I think we should explicitly set these points:
cos_newtable[COSTABLESIZE / 4] = 0.0; /* 1/2 PI */ cos_newtable[COSTABLESIZE / 2] = -1.0; /* PI */ cos_newtable[COSTABLESIZE / 4 * 3] = 0.0; /* 3/2 PI */
@Miller: what do you think? IMO we should make the cos table as good as we can, so we won't have any regrets :)
The rest of the function looks symmetric, though, and certainly much, much better than the previous one.
Thanks for checking!
Christof _______________________________________________ Pd-dev mailing list Pd-dev@lists.iem.at https://lists.puredata.info/listinfo/pd-dev