I have an issue where the "slider" for volume is near unusable for a USB-headset. Only the first four mini-steps (see Lowest volume is still too loud—how can I make it even lower?) are somehow valid volume ranges, the rest are way too high.
In the MIDI-control I can see that the dB-range is from -37 dB (0-volume) to -0 dB (1-volume, or max, the scale is between 0 and 1). With mini-steps (see above) the increment is 0.016-volume, but the first step from 0 to 0.016 gets the dBs from -37 to -32.37, and each following mini-step is roughly 0.5 dBs closer to 0.
I want the volume slider to step between -37 and -18 dBs instead of -32.37 (the lowest mini-step with sound) to 0. Is this doable somehow using the normal vol up / vol down keys?
As a comment, I think the actual dB-values are way off, but that probably depends on the fact that it is a USB-headset.
Edit
Added image below, note that this is set manually, I cannot get it this low with volume keys. Lowest with volume keys is "value" at 0.016 and db at -32.37, whilst I'd like 0.001 and db at -36 as I have now (via applescript).
Best Answer
I also had this Problem a years ago by then I found no way to do it with OS X Onboard Tools didn't even try nor know the AppleScript Workaround (this would have been enough for me i think) anyway.
My Solution I ended Up using was to use Soundflower https://rogueamoeba.com/freebies/soundflower/ a Software based 2 or 64 Channel Audiorouting Tool.
Maybe it also had some inpact on my decision to use it that I already used it for Music Production.
I think the Way I used it to do what you're looking for was as follows:
Soundflower shows up as 2 Separate Audio Devices on the Audio-Midi-Setup a 2Channel and a 64Channel Device both with individual Soundlevel Sliders.
So I just set the System Out under Systemsettings to Soundflower 2Channel and then set a Audio Level on the Soundflower 2Channel Device.
By that time Soundflower was a free Tool don't know if its still free and also am not 100% shure if I really only used Soundflower back then or together with Jack http://www.jackosx.com.
As I said it was years ago and I can't remember all exactly also I now have different Audio Setup much more complex so i'm currently not able to try it out by myself.
Hope it still helps you.