AudioEffectFilter description and functionality is incorrect

[nezvers]

Godot version

v4.1.1.stable.official [bd6af8e]

System information

Godot v4.1.1.stable - Windows 10.0.19045 - Vulkan (Mobile) - dedicated NVIDIA GeForce RTX 2070 SUPER (NVIDIA; 31.0.15.3203) - Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz (8 Threads)

Issue description

I have an audio engineering and audio forensic background and I'm making an ear training app, but run into problems:
AudioEffectFilter description: Allows frequencies other than the cutoff_hz to pass. is description of BandPassFilter functionality.
AudioEffectFilter functionality: It cuts everything above the cutoff_hz, making it a LowPassFilter.

Biggest frustration comes from the fact that there are all kinds of filters except the most essential ParametricEq (additive and subtractive frequency filtering with changeable frequency and resonance). And all hope fell on the AudioEffectFilter since it has gain property, but it doesn't function.

Steps to reproduce

• add AudioStreamPlayer with music
• add AudioEffectFilter to the master bus with cutoff_hz as 1000
• high frequencies are inaudible

Minimal reproduction project

AudioEffectFilter.zip

[Calinou]

Biggest frustration comes from the fact that there are all kinds of filters except the most essential ParametricEq (additive and subtractive frequency filtering with changeable frequency and resonance).

This is implemented by #30578, but it needs a rebase and further work before it can be merged.

[nezvers]

Amazing news!
But what's going on with confusing description and functionality

[Calinou]

But what's going on with confusing description and functionality

I think the expected behavior should remain to preserve compatibility with existing projects. We should only modify the class reference description to match the actual behavior.