System-wide sound effects on OS X? Is there an option in macOS which would allow a 3rd party to install a system-wide sound effect on an macOS machine? Something similar to Windows APO (Audio Processing Object) technology:
&quot;Windows allows OEMs and third-party audio hardware manufacturers to include custom digital signal processing effects as part of their audio driver's value-added features. These effects are packaged as user-mode system effect Audio Processing Objects (APOs).&quot;
The technology enables users to easily enable/disable system-wide sound enhancement algorithms (see screenshot).
From the system tray:

From the device settings:
You can add Audio Unit effects, which can be used by any AU-capable audio app. Example with Apple originals &amp; third party additions…

Generally, you cannot plug these directly into the Mac's audio output, you need an app capable of accessing them. Apps such as SoundSource can do this for any app or all, at simple general consumer level, intercepting between app or system output &amp; the intended hardware out.
There is, of course, already a large market for these effects as stand-alone processors, in the pro audio world. From free to expensive.
If you search &quot;VST plugins&quot; you'll find many of these that come in multi-format, VST, AU, etc. VST is a proprietary format from Steinberg, but the plugin API is available for developers. Once the effect is coded (waaay beyond my abilities) then they are often cross-ported to other formats.