Creating an Experimental Reverb from Alpas Stages

Tutorial | Dec 05, 2020

I tried to create a reverb by using an all-pass stage as the foundation. I used a stereo split and placed one all-pass on the left channel and the other on the right. I used a long delay and a blend knob to fit the original signal back into the patch, and then I added a modulation amount to the delay to give the reverb a more metallic feel. I then added a low pass and high pass filter to remove any low end frequencies and experimented with adding multiple all-pass devices to create a more complex reverb.

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Questions & Answers #

Maybe you dont watch the video, here are some important takeaways:

What is an all-pass filter? #

An all-pass filter is an electrical circuit used to affect the phase of a signal without altering its amplitude. It works by allowing the signal to pass through with no attenuation, but changing the phase of the signal as it passes through.

How does a reverb work? #

A reverb works by sending a signal through a series of delays, filters, and all-pass filters to create a reverberation effect. The signal is sent through each of the elements, with each element adding a different element to the sound. The signal is then mixed back together to create the reverberation effect.

What is delay modulation? #

Delay modulation is a technique used to add movement and interest to a sound or signal by changing the timing of its echoes. This can be done by adding an LFO to a delay effect, or by changing the delay time manually.

Transcription #

This is what im talking about in this video. The text is transcribed by AI, so it might not be perfect. If you find any mistakes, please let me know.
You can also click on the timestamps to jump to the right part of the video, which should be helpful.

[00:00.000] So now I'm trying to create some kind of reverb and most of the algorhythmic reverbs have
[00:21.880] some kind of alpas stage and every reverb is different basically and how is such a structure
[00:34.560] is built. So some reverbs just use alpas and then have different pitch pitching delays
[00:44.160] in between and so on. So it's always a bit different and every time I build something
[00:50.000] like this it sounds a bit different. So maybe I go for a stereo split here, left channel
[01:01.000] goes in one alpas, the right channel goes in this one, get the out of this and maybe
[01:07.280] just just listen to the output of the alpas. So it sounds like a delay, right?
[01:38.280] And when you have reverbs, you have sliders or knobs like this, the fusion, right? And all
[01:47.480] this means is basically that you fill in the gaps between the delay times. So when you
[01:52.760] hear the delay taps playing, all you need to do is fill in the gaps. And you can do this
[02:15.920] with feedback. So maybe we use the long delay here, go into the long delay. I use a blend.
[02:26.880] So we can fit in the original signal to the delay, go out into the long delay and back into
[02:38.080] this patch here. And maybe it will volume here at the end. And you can see how the feedback
[03:00.880] builds up over time, right? And then you feed the same signal back in every time and you build up
[03:10.320] some kind of diffusion system.
[03:40.120] So you need to find the right sweet spot of the right volume where it just starts to build up,
[03:48.280] but it doesn't exceed itself in volume. And you can hear it sounds pretty metallic because it's a
[04:08.680] feedback and it's always the same sound on top of each other. So what you do in most reverbs is
[04:17.320] to bring in a changing delay. That's also what you have here, delay modulation amount. So we change
[04:27.000] the, either the speed here of the delay or let's go for this, bring in the delay here. And then we
[04:38.440] modulate this to the amount of the delay. So maybe you'll go from random. Let's use an LFO.
[05:08.440] Now we get rid of the
[05:38.360] metallic feel because the pitch changes over time slowly. And so the signal is a bit different
[05:46.200] every time it overlaps in the feedback.
[05:56.680] And also when you see here some delays like this they have low pass and high pass so you
[06:11.400] can remove the low end a bit. whoops high pass sorry always yeah exchange
[06:38.120] these in my mind can also use multiple all pass devices here maybe.
[07:38.120] So this is basically a small reverb. And you can go completely crazy with this you can
[08:03.720] add more all pass devices you can add more stages and so on. I already built some kind of crazy
[08:11.320] reverb maybe.