All Pass Filters

[jmg8]

Hopefully someone can help me understand what this is for.
What is the purpose of a filter that let's everything through?
It seems like it does nothing at all, but I guess it's something to do with phase. I must have missed the memo. Somebody please enlighten me.

[Gamma-UT]

All pass filters are good for shifting relative phase around a centre frequency. Radio stations have used this for decades to reduce peaks and so make stuff sound louder - they use it on bass to smear out the transients. The filters are also useful in reverbs for the same smearing effect.

[vectorwarrior]

Yeah, it allows you to mess with the phase of signals, smearing frequencies over time. For an interesting effect I set up loads of all pass filters in the low freqs and sweep them all up using a multiparameter, fun for low freq sounds like kicks.

To give you an idea, check out this vst, it does a similar thing
https://kilohearts.com/products/disperser

YouTube that sucker for a better idea of the effect.

[jmg8]

Any links to more info? I couldn't find much. A few questions:
Does the central frequency get sped up or slowed down in phase?
How much out of phase do frequencies become? Is there a way to change the phase amount by using gain etc?

I like the sound of BEE sonic maximizer (when used a just a little). From what can understand, it changes the phase of the mid frequencies by putting in behind/slower than the high and low. Does anyone know more about this technique?

Thanks.