Let repeated settings add

[peastman]

A very useful feature would be a way to specify the same setting at multiple levels (global, group, region), and instead of the later ones overriding the earlier ones, they would add together. For example, I want to use CC1 to control the volume. So at the group level I specify

volume=-20
gain_cc1=20

But I also want to specify volume at the region level, because my samples aren't exactly the same volume and I need to correct for that. So a lot of them have minor adjustments like volume=2 and volume=-1. And I want to keep these separate, because they're adjusting the volumes for completely different reasons. But it doesn't work. The region setting overrides the group setting. Instead I need to combine them and put values like volume=-18 and volume=-21 in all the regions. Then I decide I actually want the volume to vary over 25 dB instead of 20, and now I need to go through all the regions and recalculate what their volumes should be.

This also applies to other settings. For example, I specify tune at the group level to set up pitch bending, and also at the region level to correct for inconsistent tuning of samples.

[plgDavid]

global_volume, master_volume and group_volume along with the standard volume seem to do what you are requesting here. [https://sfzformat.com/opcodes/global_volume]
All four volumes are additive. The catch is each of the four opcodes can be overridden in every due to how the sfz parsing logic works. Its however very bad practice to do so and potentially should be warned to the user
[Note that ARIA supports equivalent multi tiered ‘tune’ as well [https://sfzformat.com/opcodes/global_tune]

[peastman]

That's exactly what I was looking for, thanks! I didn't realize they added, since the documentation doesn't say anything about how they interact.