How To Create A Very Basic Comb Filter Using Renoise Native Devices


(dblue) #1

A little while ago, the idea was discussed to create a comb filter made from several bandpass filters. Unfortunately, due to the way it had to be structured, it was not really possible to automate all of the filters at once in an easy way (not even with a Hydra device).

Later in that same thread, martyfmelb suggested the idea of using bandstop filters instead, to create a kind of reverse comb filter. If you’re just looking for that vowel-like timbre, then this can actually work quite well.

Taking the idea a little bit further… if we stick with the bandstop filters as marty suggests, but then invert the results and mix that all back into the original unfiltered signal, we can take advantage of the way it cancels out in certain areas, and the final result is something pretty damn close to a real comb filter. Best of all, since the bandstop filters are all contained on the same track, we can easily use a Hydra device to control them all at once.

Example - (made in Renoise 2.1):
http://illformed.org/temp/2009-08-04-comb-filter.xrns

It needs some more tweaking, and it’s not a totally perfect sound due to the incorrectness of using filters in this way, but it still works kinda nicely.


[Done 2.7] Comb Filter!
(planetm) #2

nice effect, it amazes me what people manage with the native effects - I clearly need more imagination and/or knowledge!


(datassette) #3

Nice work!


(mr_mark_dollin) #4

Really interesting! This one was easy enough to understand. I had some fun taking the pattern commands out and just sliding around with the hydra master position. I now know how these sounds are made!


(dblue) #5

Yeah, it’s fun. I haven’t quite managed to dial in some really nice settings yet, but I was able to get some pretty nice vowel sounds, a bit similar to the old Delay Llama VST actually, although it’s still lacking a certain something. I’d be interested to learn a little more about the specific frequency bands that should be used for that kinda stuff, or if it’s just more to do with the spacing of the bands. Anyway… fun :)


(Winther) #6

Hi guys…

Firstly dBlue i dont understand why you feel the need to put lfo’s between the control path of the hydra and the filter’s? This is quite possibly caused by me being daft… but anyways i have prepared a example of my own.

In this example there are two tracks one with dBlue’s method that i have simplified “simply” by removing the lfo’s between the hydra and filter devices… Track two contains my own understanding of a comb filter, achieved using the chorus device since the delay device doesnt have the required resolution of delay time. I may have completly misunderstood the comb filter, and my version is without question less flexible but i does offer a very high number of “teeth” for the filter. Simply fiddle with the min/max settings on the hydra for various sweeps.

The example given in this post may or may not contain arbitrary lfo's for the sake of displaying sweeping values in said example.  

/Winther


(dblue) #7

You’re quite correct - there’s absolutely no need for them, and I actually wasn’t using them at first, so my example was initially the same as your rework. I just thought it provided a nice way to simplify the min/max parameters into a more familiar [0% - 100%] range, rather than directly entering frequency values. You can see they’re not actually behaving as typical LFOs since the amount is set to 0%, so I was just taking advantage of the offset parameter they provide to remap things. But that’s really nothing more than my own personal taste… no big deal!

[Edit]
Ok, I removed the LFOs from the example now. They were unnecessary and just a personal thing for me, and don’t really help to make things as clear as possible. :)

Again, you’re quite correct. As you’ve demonstrated, a comb filter is really nothing more than a short delay line.

To be more accurate, I should have said “comb-like”, or perhaps “formant filter” or “vowel filter”, something along those lines. It’s just quite easy (for me, and probably some others) to immediately think of a comb filter when trying to achieve that particular sound, because they are so closely related. I also think the greatly reduced number of peaks in this simple recreation provides a much more interesting and musical sound.

Anyway, thanks for pointing it out and providing your example. :)


(dblue) #8

http://illformed.org/temp/2009-08-04-comb-filter-fun.xrns

Just for fun, hahah :P


(Winther) #9

Im not sure how my post sounded when read by another, but i hope it didn’t patronizing or something like that. I should probably use more smiles <_< but i guess thats something ill have to work on…

/Winther


(martyfmelb) #10

Hah, comb-filter-fun is awesome! Additive synthesis that sounds like subtractive = yummy :)


(danoise) #11

Give the man a rock, and he’ll shape it into a diamond :wacko:


(MonoGraph) #12

Tried doing it with a Delay -
With Renoise Delay controlled through two HYDRAS (one for delay time, the other for feedback).
I found it not that great until i layered up another delay - i think this gave it a better feedback gain.
MDA delay seemed a bit smother than the Renoise delay.
And then i thought…
Why not stack up two choruses like in Winthers example.
So i tried it… routed it through hydra etc…cranked up the feedbacks etc… and it crashed the audio somehow… had to restart renoise.

:yeah:

Why make tunes when you can layer FXs all day long? :w00t:


(centipus) #13

this i a great technique!! i’ve been abusing it for the past couple of days and boy has times been fun! thanks for sharing dblue


(Johann) #14

:D :D :D


(Djeroek) #15

great stuff Dblue!

I think I have some notes on which filter settings, create which vowels but can’t find them :(


(BYTE-Smasher) #16

Actually, I’m thinking it is a real comb filter. It seems to me that phase canceling a bandstop against the original makes a genuine bandpass.