The IDs of new sound effects are the numeric order in the corresponding action 11 plus 49 (73 decimal), i.e. the first entry in action 11 has ID 49, the second one ID 4A and so on. You must have an action 11 before this action 0, or else no new sound IDs will have been defined, and thus their properties cannot be set. You cannot directly set the properties of IDs 0..48 that refer to TTD's original sounds, except by overriding these sounds using property 0A.
|08||B||0.6 2.5||Relative volume|
|0A||B||0.6 2.5||Override old sound|
Relative volume (08)
This value defines the volume of the sound effect relatively to the main volume. The maximum is 80h (0dB), the minimum is 0 (-24dB).
If unset, it defaults to 80h.
This value is only meaningful in the DOS version, where there are limited mixing channels. The lower this byte is, the higher the priority of the sound is. If a sound needs to be played when all mixing channels are busy, the mixer will stop one of the lower priority sounds. Less important sounds should have this byte higher.
If unset, this defaults to 0.
Override old sound (0A)
Overrides the given old sound (00h..48h) with the current one. This also changes the sound effect to use the relative volume and priority associated with the current one.