Sometimes, simple stuff matters. DJ mixers like Pioneer’s DJM-800 have simple, single-knob low- and high-pass filters. Laptop software often doesn’t. Enter FZero, with his free and open source Single Knob Filter to fill the gaps. (Windows-only, built in SynthEdit, but it’s open source and schematics of the basic signal processing are available, if anyone wants to translate this to Mac.) Drop this into an insert in a tool like Ableton Live and go play.

Single Knob Filter [Project Page]
SKF-VST at Google Code [Source, VST Download]

It’s apparently a big improvement on an Ableton forum solution that used 127 different filter instances in a rack.

I’m aware of the goodness of Single Knob Filter thanks to the Aurora open source DJ mixer project (see yesterday’s write-up); they assign an instance of the plug-in on each of the Aurora’s two mixer channels. Aurora’s Matt originally had the SKF plug-in in their Ableton template, but I encouraged them to replace it with Ableton’s Auto Filter for cross-platform compatibility and ease. That said, for plain DJ filtering, this it the One True Knob.

Now, go forth and use it on some crazy experimental noise soundscape you’ve been working on, just to spite cliche.

The Pioneer DJM-800, caught in action by talented Flickr Fotographer Manuel_P (see blog).
  • single knob filter appears to have two knobs

  • Well, the filter is one knob. Resonance doesn't count? 😉


    some folks @ the abletonlivedj forum will be very excited about this….

  • George Kilburg

    Yes, the concept of a filter cutoff frequency being controlled with only one knob is a new one on me!

  • Whoa, this made my day. It was rather crappy up until now. 🙂

    I'm absurdly flattered. Really. Thanks.

  • There's no source on the Google Code page. 🙁

  • @Ortzinator Yes, there is, in Synthedit format. I'm not a C programmer, sorry.

  • Oh it's in with the binary. Cheers.

  • George Kilburg

    The second thing I don't understand is this:

    "It’s apparently a big improvement on an Ableton forum solution that used 127 different filter instances in a rack."

    Why do that?

  • tobamai

    Sounds to me like someone over at the ableton forums made a rack full of 127 different filters all set to different frequencies. Then he bound one knob to cycle through them.

    The better solution would be to pick your favourite low pass and high pass filters and then bind the top half of a knob to control the low pass and the bottom half to control the high pass with zero on both filters in the center. You can do this in Live 7 with the midi binds, I don't know about other versions. You could just write some midi translator script to do parse the one knob's cc into two different cc's (with glovepie, maybe bome's).

    I'm glad I'm not the only one who thought 127 different filters sounded like a really bad solution.

  • @tobamai, since HP/LP filters act inversely, i'd probably map the high pass to the top half of the knob and the low pass to the low side with center value = 127 for LP and 0 for HP.

  • jason

    @seismo: You can do this with Traktor DJ and my VCI-100 controller. I just discovered how to set it up properly. Totally freakin' sweet.

  • tobamai

    Yeah, I caught my mistake but I don't see a way to edit the post. Anyways, the idea is that when the knob is at the center the filters don't affect the audio at all.

  • Ashley

    Oh dear. I can't believe anyone would care about this. There's got to be like 10,000 other crap stock standard synthedit filters available that could do more than this.

  • If this faithfully emulates the sound of those Pioneer effects it's gets my achievement for the worst sounding filter ever.

  • gbsr

    my question is this: why would this be a better solution then the ableton rack you mention? because, racks and native live devices uses no cpu unless they have a signal (other then the very few cpu cycles it takes to piont the vectors). so it wouldnt exactly be anything to gain by getting this as opposed to the rack, except a stupid vst ui. oh, ofcourse as for the sound i dont know, but if they are identical in terms of sound, there shouldnt really be any difference, other the fact that one thing has a ui and the other has a native ui.

  • gbsr

    umm yeah, to clarify: native devices uses no cpu unless they have a signal. racks isnt true per definition since racks can contain vst plugins aswell as bative devices. but if a rack uses native devices only, then its true.

  • There were a couple of free Single Knob Filters released on this KvR page

    Including my own version, which is hand coded and uses the host GUI

  • Pingback: Freeware: Single Knob Filter VST wie DJM-800 « DIGITAL AUDIO SERVICE()

  • @all:

    My intention was to make something that used less cpu and was less clunky than the rack with 127 filters. Contrary to what @gbsr said, the former filter rack used around 10% of my cpu while idle and up to 25% while active, so it was impossible for me to use on my machine at the time (Pentium M 1.5 notebook).

    I never said it was an ideal solution or that better alternatives don't exist. In fact I would really like to know some C++ to make a proper plugin with a (more) kickass sound, but for now I'm satisfied with this (and I don't have time to learn C++ properly right now).

    I really think Sythedit's filters sound awesome anyway (they self-oscillate!), and the thing is open-source after all. Want to make it better? Download it and modify it! I'm curious to see what other people can add to this (LFO? Better gfx? Who knows?).

    By the way, I tried to make a simpler rack on Live before doing it with Synthedit, but it didn't sound right because Live doesn't have a way to apply curves (exponential, parabole etc.) to the controllers. The linear curve makes it very difficult to make a natural-sounding single knob filter.

  • Please…. oh pretty please will someone translate for us Mac peeps. 127 Autofilter instances sounds all too familiar….

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  • gbsr

    @fzero, +1 on the curves.

  • Ashley

    @ Andrew:

    go to There's hundreds of free mac filters that will do 100x times what this can. This can't be translated to mac. But there's tonnes of free filters out there that look better, sound better, and have more features.

  • Correct me if I'm wrong, but aren't there two knobs on that single knob filter?

  • Ashley

    Yeah, it's obvious that whoever made this is about as good at counting as they are at making software.

    Sorry, i just had to.

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  • ridiculous

    you ppl are absurd, i can’t believe this even got a mention on create digital. any newcommer to synthmaker or synthedit with a just a basic understanding of filters could make this plugin within 3 minutes.

  • MAC

    OSX version?

  • switched from pc to mac and i badly miss this vst… any news on a mac version?

    or a cpu friendly alternative?