copy a matrix into another one, with offset

Julien Bayle's icon

hi there,
a final output matrix, displaying blank screen at the beginning
another matrix with content changing each x seconds.
both same width, but the second one is 1/8 height of the first one.

The big one has to be filled progressively, each x seconds, by the content of the small one, using offset
in a cycle, after x second, the first 1/8 is filled.
then after x, the second 1/8 (the first 1/8 still contains the previous stuff)

etc till the end where all become blank again

struggling with @usedstdim and the other companions in tutorial 16 and the content of the smallest is always copied at the bottom
strangely.

Max Patch
Copy patch and select New From Clipboard in Max.

Here is the machine:

any leads would totally unstick me :)

Rob Ramirez's icon
Julien Bayle's icon

I guess the one fitting the most is the final one (in the last post) but I still understand the underlying idea :-/

Using matrix operation like +, if I could store the new bands in a total black (empty) matrix, I could sum this one each time with the last one and accumulate the values..