Flanger & Phaser Depth parameter improvement

[Be-ing]

I am trying to figure out better behavior for the Depth parameter of the Flanger and Phaser effects. Both of these create their effected sound by mixing the dry signal with a delayed copy of itself to create comb filtering. Simply adding the dry and delayed signals does not work well because the volume increases quite a bit when the Depth parameter is at its maximum. I have come up with a formula that keeps a roughly consistent volume but it is still not ideal. I cannot hear the effects until the Depth knob is up half way. Simply truncating the range of the Depth knob to 0.5 - 1 would not work because the effects should not change the input when the depth knob (which is linked to the metaknob by default) is fully down. Any ideas for how to improve this further?

[daschuer]

I think we should close this and fix the flanger towards this:
https://www.premierguitar.com/articles/Get_More_Out_of_Your_Flanger

Our depth parameter currently just wrong named. It is actually a "Dry/Wet" parameter sometimes labelled "Mix" on some Stomp boxes. The original lfoDepth parameter or Width should effect LfoAmplitude.

It would be also Cool to have an Manual knob to tweak kAverageDelayLength.
In case Depth is 0, you can sweep the delay manually.

I am also curious how the "Regen" feedback loop sounds.

[Be-ing]

I tried making the Flanger LFO amplitude controlled by an effect parameter knob, but it didn't seem very useful. Perhaps I didn't choose an appropriate scale of values. If you have different ideas for improving these effects, I'd be happy to test them. I'm not certain this PR is the right way to go, it's just an attempt.

[Be-ing]

Closing in favor of #1362.