Help me understand phasers and possibly build one in the ER-301

My knowledge of phasers is limited to the basic diagram of some all pass filters in series with feedback. Then, I think each all pass filter has a different central frequency (related to each other, how?) about which the input is shifted in phase. Thus you get peaks and notches, which you move up and down by modulating the frequency of the filters.

As there’s not a dedicated generic allpass unit, is Joe’s Schroeder All Pass filter somehow suitable for this, even though the only parameters are delay and gain? I naively threw 4 in series, but the result was not what I was aiming for.

Any help here would defiantly be appreciated! I normally try to be a more self-sufficient, but what I’m finding online is either way too basic or too technical for somebody w/my lack of time and technical background.

I just built one myself (I think?)

(All pass filter) * 4 in series (4 stage, 2 pole)

(All pass filter)
2-band:
1st band: LPF
2nd band: HPF to bipolar vca @ -1

set it all within a custom unit and move the f0 of all filters.

edit:
Add a mixer in front of the all pass filter chain and assign from the end for feedback.

Dry/Wet for depth. Add more all pass filters in series for more stages, more poles.

I have attached the relevant section of the wikipedia:https://en.wikipedia.org/wiki/All-pass_filter#Implementation_using_low-pass_filter

edit 2:
I’m running through this excellent site and trying to implement what i learn through the er-301. Feel free to join me!
http://www.spinsemi.com/knowledge_base/effects.html

4 Likes

Will give this a shot and report back. Thanks!

Would you mind letting me know what frequency settings you used for the filters? I’m def getting nice phaser-y sounds, but they’re not particularly deep.

How many stages have you tried? I think the depth of the effect has more to do with how many “notches” you can create and how much you have mixed this with your original signal over the frequency of the filters. The frequency range I had used ranges from fully open to fully “closed” - I think the frequency is usually modulated with an LFO anyway.

edit: You can also try to make a flanger which is similar and just as easy to make in the er-301.

edit 2: Oh! and make sure you use a source signal with enough high frequency content so you can hear (or see in a scope) the effects of sweeping the frequency. I was using white noise (e.g. a sin wave would be a less than ideal source).

edit 3: To answer your question about notches in your original post:
"A phaser with n stages generally has n/2 notches in the spectrum, so a 4-stage phaser will have two notches.

Additionally, the output can be fed back to the input for a more intense effect, creating a resonant effect by emphasizing frequencies between notches. "

edit 4: some inspiration: https://www.youtube.com/watch?v=1wDHraG6JMI
you can do it!