Thanks for the positive feedback OMG, Wallace, Tin, racer-x and RJKD.
Some 3D fractal programs can use sound to make fractals but I haven't seen anything like that in Gimp.
These animations are made with maths and music has a maths component so maybe one day?
I found animations only work if the MM 'animated' filters are applied first and the non-animated filters are applied later.
(after the mixer in above) The 'geom_rotate' filter is one of the standard MM filters and it's useful for rotating an animation
into any position. I guess my breakthough was discovering that nearly all MM filters work on animations but only animated filters
can make animations. So the whole of MM can be applied to animation.