[PD] [tabwrite4~], is it possible at all?

[katja]

Hello,

In order to build a variable speed sound-on-sound looper I was looking
for an object that can write at fractional speed, analogous to the
interpolated reading of [tabread4~]. Indeed I found C code for
[tabwrite4~] in ggee/experimental, but a quick test revealed that it
doesn't work properly. In a flash of optimism, I planned to rewrite
the code, but soon stumbled upon questions.

It seems to me that 4-point-interpolated writing would mean: write
values to 4 indexes at a time, just like [tabread4~] reads from 4
indexes at a time. While writing 4 values, recently written values
must be taken into account, not bluntly overwritten. So two existing
values, x[n-2] and x[n-1], should be somehow integrated with new
values, if the writing direction is positive. That should be a leaky
integration. Imagine the write pointer doesn't move; the values should
not build up then. But how much should it leak to get the right
balance?

Does anyone have knowledge of this? It would be cool to have
[tabwrite4~] in Pd-extended. I'm prepared to spend time on it, if
someone can assure me that the concept is viable at all.


Katja