What Is An Allpass Filter?

This has bugged me recently, and I was wondering if anyone here has knowledge on this matter, and might be willing to shed light on this.

From what I gather, it seems that allpass filter acts like a delay of sorts. Am I right?

I’ve tried to build a renoise native allpass filter by routing source signal into two separate butterworths, a highpass and a lowpass, and combining the result. (Linking the cutoff with a hydra) The result, when played together with the source audio sounds to me just like a ‘static phaser’.

Why would one use an allpass filter instead of a delay? Or a static phaser?

How does the cutoff frequency of the allpass filter fit into all this?

Also: are there specific uses for an allpass filter? I understand that this might seem a dumb question (like: are there specific uses for a delay… uhmmm.), but bear with me; I’m a complete novice on sound.

EDIT: wrote stupid things in a hurry. Fixed.

In my understanding they’re nothing but phase correction circuits that introduce some measure of delay into the processing chain without the need for storing any signals in memory, like a delay does. So really relevant to hardware design, not so much in DSP… I think?

Yeah if I recall correctly from one of my classes the all-passfilter delays certain frequencies so that phase shifts occur. You can use it to fix phase problems in signals for instance.

Not sure what to add but you’re all pretty much correct.

An All Pass Filter will add delay to a signal, the type of delay depends on the type of filter design so may be linear phase or may not.

Phasers (in the hardware world at least) are made out of a combination of All Pass Filters, I think to get good results it has to be an even number and will often be 4-8 or so. I believe the Stages parameter of Renoise’s Phaser is how you set how many All Pass Filters are modelled into its calculations but I’m only guessing.

You say if you want a delay why not just use a Delay. How do you make an analogue delay device? By using an All Pass Filter.

Allpass filters or static phasers have a very distinct audible effect, and are definitely useful in your arsenal.
They can sound great on kickdrums, and particularly good on low sawtooth notes, they give everything a kind of laser-pulse snappiness.
Cheesy electro-house like Deadmau5 and Skrillex and all that shit is absolutely drenched in this effect.

Anyone know of a free plugin that does it?

You can chain up like 6 arguru stardusts with nothing but the bass phase rotator switched on to 8 poles to get something very similar to Uhbik-P (which is what I use normally)