add tensorboard scalar logging for audio filter variables

[dmarx]

~~corresponding losses and computed weights don't seem to be getting logged either.~~ nevermind, I had display_every set to an arbitrarily high value to suppress this reporting, I think for debugging something.

oh hey, maybe there could be a "dry run" animation mode or something to just compute per-t weights and such. using that kind of outputted file as an input is probably identical to the "csv" input gandamu was talking about in his personal tooling. maybe he can integrate that piece?