Hi Piotr, I have produced rolls on standard 2" spools, they play
for just over 8 minutes, and the spools are about three quarters full,
so there is leeway for a few more minutes play time. If I use a larger
spool I can get around 22 minutes play time.

I use thin waxed paper which is very strong, and slightly thinner
than the QRS paper. The rolls are not condensed or shortened, they are
punched as they were recorded. I do not like condensing or shortening
rolls before perforating, as it tends to mess up the repetition.

Additionally, the shortest note you can have on a player piano is one
single hole -- you cannot shorten more than that, so if a roll is
shortened that has single holes, you are already messing up the
arrangement. This is very noticeable on reproducing rolls,

I have purchased Duo-Art rolls that have been condensed or shortened,
presumably to save paper, but they do not play correctly, and I will
not be purchasing any more.

QRS XP rolls play for 6 minutes or more, like Oklahoma XP-121B, but
these are specially arranged to account for the slower playing Tempo.

Regards,
Paul Bell