> <snip>
I think I understand why these errors are generated. It would appear that \fz is not intended to be used as a dynamic - it is not mentioned in the NR. Nevertheless, is is defined as a dynamic script in the LP file dynamic-scripts-init.ly. Unfortunately, there is no corresponding entry in midi.scm to assign a “factor of total volume” for this dynamic, without which the midi performer is unable to do anything sensible.
It is possible you might get the results you want by rewriting the snippet as:
> music = \relative {
> c''2\p\< c |
> \tag #'pdf c1\fz\>
> \tag #'midi c1\f->\>
> c\p |
> }
>
> \score {
> \keepWithTag #'pdf \music
> }
>
> \score {
> \keepWithTag #'midi \music
> \midi {}
> }
>
Good idea; thanks for the suggestion. I'll give it a try over the weekend, once I've worked out the ramifications for other tags in use.