Effective Effect Filtering

Do you think plug-in filters are good for adding trance-gate pulsation and little else? Check this article out to learn just how much more can be done with these versatile devices.


by David Baer, Mar. 2014 


Electronic musicians who cut their teeth on subtractive synthesis may be forgiven for dismissing filter plug-ins as effects of little value.  If the heart of a subtractive synth is the oscillator, the filter is the soul.  In modern synths, filters are polyphonic, with each note getting a dedicated filter process with per-note modulation (envelopes, LFOs, etc.).  With a filter plug-in inserted in the signal path after a synth, there’s only global processing.

Certainly, my attitude was dismissive until recently.  But circumstances prompted me to investigate further and I was pleasantly surprised that filter plug-ins could do far more than just impose a trance-gate quality to the sound, which was my original suspicion.  So, we’ll be looking at some of those applications in this article.

Although I’ll be using Fab Filter’s Volcano effect, many of the sound manipulation possibilities that I’ll be demonstrating will be transferable to other brands of filters, either directly by using multiple instances of the filter plug-in and sends.  But it should be made clear that Volcano is probably more capable than most filter plug-ins available.  That only makes sense.  If you’re going to call your company “Fab Filter”, then your filter plug-in had better be pretty special.  🙂 

We’ll be looking at a few Volcano factory presets (from which there are a vast number to choose).  Don’t worry if you know nothing about this device.  We’ll be deconstructing the presets and explaining the details as we go.  Once you see some basic applications, creating your own presets should be easy to accomplish on whatever type filter effects you have available in your DAW.



Although I’m not going to do a full explanation of the intricacies of Volcano, some background is in order.  First, Volcano has four independent stereo filters.  These can be configured in series, parallel and permutations in between.  Each filter can be low, high or band-pass with 12, 24 or 48 dB/octave attenuation.  Nine different filter models can be selected, ranging from smooth-as-baby-skin to rough-and-tumble, with self-oscillation capability on a number of them.

The plug-in can also do filtering independently on each stereo channel or can independently operate on mid and side signals.  In this case the number of filters per channel must be a symmetrical one or two (but when there are two, they can operate in serial or parallel on each channel).

Volcano’s power and flexibility is mostly due to filter modulation possibilities.  One key aspect of this is the XLFO modulator, which can act as a conventional LFO, a sixteen step sequencer or anything in between.  ADSR envelopes, envelope followers and MIDI modulation (CC, velocity, note number, etc.) are also possible modulation sources. 

More than any other plug-in type, I believe that filters will frequently benefit from being able to receive MIDI input.  Some DAWs make this easy, others not so much.  You’ll be in a better position to effectively employ filter technology if your DAW is in the former category.

Volcano is a filter powerhouse as you’ll hopefully see in what follows.  Be assured, Volcano is not the only option in this area, however.  Ohm Force, FXpansion, and others have effects worth evaluating.  They may not sport all the bells and whistles found on Volcano, but they have many and also most have more modest pricing to recommend them.

A note about the audio examples is in order.  I’m using a slightly modified factory preset from the LuSH-101 synth here for all my examples.  None of the examples are intended to be compositions worthy of note; they are just simple musical passages that illustrate the sound manipulation supplied by the filter.  Where appropriate, examples will be start with a brief unfiltered passage to set the stage, after which you will hear the filtered sound.  No other processing is in the signal chain.


Filtering as EQ Alternative

Let’s start with the most basic of applications: using a filter to manipulate the audio spectrum.  The image below shows the Enhance My Synth preset.  It could hardly be simpler – there is zero modulation in the works.  We have three band pass filters running in parallel with gentle 12dB slopes and frequencies of 52Hz, 17KHz and 22KHz respectively.


So what’s the big deal?  Why not just do this with EQ?  The answer lies in the fact that with the filter, we have a dry/wet control, something you’d never see on an EQ (at least I’ve never seen one).  In addition to sounding subtly pleasant, several options exist: one is to gently modulate the Mix with a slow LFO and another is to MIDI-map an external controller like the mod wheel to control the mix.  The results can be heard in the audio clip that follows, where a passage is first heard alone and then with the filter enabled.  The filtering results in an extremely subtle change in the sound which might not be evident on lower end playback equipment (but will hopefully make it through the transition to mp3).  Though subtle, I find the results to be quite lovely … I fully expect to be returning to this preset frequently.

     EQ Alternative Demo


Filtering for Stereo Enhancement

Let’s take the previous idea a little further and put some modulation into play.  This time we have two low-pass filters, initially at 18Kz and 84Hz respectively, and panned mid-right and mid-left respectively.  We also have two sine wave LFOs, the first with a languorous cycle time of eight bars, the second of a slightly-less-slow four bars.  The slower LFO modulates only the first filter’s cutoff.  The second does triple duty, modulating filter two’s frequency and both filters’ resonance (peak) values.


As you might expect, there’s a pronounced unhurried sweep (cycles of four and eight bars being at work).  In this case, and in all the remaining audio examples, the results are far from subtle.

      Stereo Enhancment Demo


Filtering for Stereo Movement

Next, we can take the previous idea one more step and use the sweeping to produce some left-right animation in the stereo soundstage.


This time we have two low-pass filters and a high-pass filter (the high-pass is not modulated and could easily be omitted if your filter effect only has two filters).  The filters all run in parallel.  The two low-pass filters with moderate resonance are initially set to 10 KHz and 12.5 KHz.  Once again we have two sine wave LFOs cycling at eight bars and four bars.  The first LFO modulates LP filter one’s frequency and negatively modulates LP filter two’s pan position.  The second positively modulates LP filter two’s pan position and LP filter one’s frequency.  So, now we again get a sweep, but this time there’s movement as the two LP filter’s panning position slowly changes.

     Stereo Movement Demo


Getting Creative

So far we’ve been relatively conservative with filter applications.  Let’s look a little further into some creative possibilities.  With filters, there’s really no limit to what mayhem you can introduce into an audio signal, but in this case we’ll keep things within reasonbly polite boundaries.  This setup is fairly simple: a low-pass and a high-pass filter.  We have a single LFO with a three-stage wave form modulating filter two’s frequency.  Don’t be confused by the fact that filters one and two are linked.  This is a design-time convenience only and does not affect the modulation.


Oh yes, and one more thing.  This time the filter is operating in M/S mode.  The low-pass filter acts upon the mid signal and the high-pass upon the side signal.  Since our input wave form isn’t particularly interesting from a stereo perspective, we’re possibly not hearing this preset to best advantage, but it does add a rather pleasant bubbly froth to the audio:

  Demo – But of What?


Let’s Trance It Up (If We Must!)

I suppose we have to look at a trance-like filter application if we’re to say we’ve covered this topic thoroughly, so let’s get it over with.   🙂  This time we’ve got a low-pass and high-pass filter in sequence, with the cutoffs and peaks linked.  Two LFOs are operating at a much faster clip than we’ve seen so far in this article: cycles of one-quarter and one-eight notes are set.  The wave form can be seen from the image.


The first LFO negatively modulates filter one’s frequency (modulator polarity flipped) and filter two’s frequency (not flipped).  The second LFO does the same, but at a different speed and with somewhat different depth settings.  It also throws in some shallow pan modulation of filter one for good measure. 

The result is a predictably pulsating filter output, probably right at home in a typical EDM production:

      Trance Demo


 Self-Oscillation Possibilities

Next we’ll look at a preset that is probably of limited musical value for most musicians, but it serves as an excellent illustration of what happens when resonant filters can self-oscillate.  Self-oscillation means that the filter is producing sound of its own volition, not just altering sound coming into it.  We have a single band-pass filter with a steep 48 dB slope and a high peak value.  We use an 80/20 percent dry to wet mix (set in the filter itself, even though the mix can also be controlled by the mod wheel in this preset).


What’s special about this example is the pattern seen in the LFO, or extended LFO (aka XLFO in Volcano).  The initial frequency is approximately that of C above middle-C (MIDI note 72).  The XLFO steps raise the frequencies in step with the C-major scale to an octave higher (MIDI note 84).  So your composition is not in C major?  Well, you would need to skip using this preset or “retune” the cutoff and XLFO steps accordingly.  In any case, listen to the results below.  Note that the self-oscillation continues after the synth stops.

   Self-Oscillation Demo


And More Self-Oscillation Mayhem

Let’s close with a more whimsical application of self-oscillation, the preset aptly named “Arcade Noises”.


In this preset, we have four steep band-pass filters in parallel.  Four XFLOs are running and they cannot all be seen in a single screen shot, so the preset is shown in multiple images.  Much the same thing is going on as in the previous example.  The first three XLFOs modulate frequencies in discreet steps.  XLFO one and three freely run at set frequencies.  What’s new this time is XFLO four.  It’s a triangle(ish) wave that modulates the frequency of XLFO2.  Delightful anarchy ensues, as can be heard in the audio clip.

  Self-Oscillation Mayhem Demo




If you started reading this article with the attitude I held just a couple of months earlier, then hopefully you’ve acquired a better understanding of the role filter plug-ins can play in your music production.  The only reason I had Volcano on my system in the first place was because it came as part of the three-piece bundle.  I badly wanted the other two and the bundle price was attractive.  Once received, Volcano sat there on my DAW machine lacking any love for a long time.  My mistake.  I think it has ended up being the pick of the litter!

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