Stereo Tool

Yes, but on Android there is no good way to get to the audio. If we could get access to audio from other programs it would be interesting, without that, it would require you to use a sound card for input, and that makes it not very useful.

Yes, you can.

Have a look at things like Poweramp Equalizer (standalone app)

It can take audio from any other known audio app and process it.
And with a toggle from adb (giving extra permissions) it can do all apps and process _all_ audio.

The big question is if this is just controlling an EQ that's already available in the phone's hardware or software, or that it actually grabs all the audio, changes it and then sends it back to the phone. So far I've only been able to find equalizers, nothing that really does anytihng more.

I don't know how to find out what they did exactly for this specific app.

Differences to other rootless FX apps
Regular rootless audio effect apps on the Play Store all essentially work the same way: Android has several default audio effects built into its operating system that these apps can use without any special permissions. Here's a list of those: https://developer.android.com/reference ... udioEffect.

Being restricted to these default built-in audio effects is problematic if you want to implement any advanced custom effects such as Viper or JDSP, because Android does not allow apps to access & modify the audio stream directly.

To work around this problem, RootlessJamesDSP uses a bunch of tricks to gain full access to the audio stream of other apps. This is done via Android's internal audio capture. This allows RootlessJamesDSP to apply its custom audio effects directly without relying on Android's built-in effects.

Unfortunately, these tricks are not 100% reliable and introduce some limitations. Apps such as Spotify block internal audio capture (they don't want people to record their songs), and because of that, RootlessJamesDSP cannot directly access the audio stream of that app. This is the reason why a special patch is required to disable this DRM restriction inside Spotify's app. Patches for other apps with these DRM restrictions do not exist, but are possible to do.

Oh, I missed the "rootless" part of that one! It doesn't work on my phone so I guess I'll have to get a new one to test this; they only iist 2 phones on the site on which it's confirmed to work... not a lot.