Sidechain for a total noob

Hello all. I have searched all over this forum, found a few posts about using SC LADSPA plugins. (I’m on ubuntu.) I’ve tried to emulate what other people are doing, but I seem to be failing. I have never really dealt with sends before in ardour, so that might be the cause. Essentially, I need to sidechain a bass against a kick, so that the bass goes down when the kick volume is high, etc. I’ve been adding an SC3 plugin, but I get an error stating that “this plugin is bugged, there are 3 inputs and only 2 outputs, unless it is a sidechain plugin.” Well no shit ardour, THIS IS A SIDECHAIN PLUGIN.

But even if I do get that working, I’m not really too sure about how to work the sends. Do I put the kick input in it’s own, first send, and then have two bass inputs in a second send? Thanks.

I was just (moments ago) using SC3 for exactly what you’re trying to achieve (the David Guetta style ducking) and realized something you may want to look into. Although the triggering for SC3 comes from input 1, the amount of compression applied depends on the volume of the material coming into inputs 2 and 3. So to get the kind of pumping style you’re after, try normalizing the track you’re trying to squash (the bass), and then add the “simple amplifier” to the track you’re trying to squash BEFORE the send to SC3 (whether you use a send or just route the output of the track). That way, if your input is pushing +10 db (for instance) at the SC3 input, whenever the compression is triggered by the kick (at a -30db threshold for instance, with a 1:10 ration), a +10db signal on the bass compresses to -26db. Then you can just turn down the compression bus to match the levels of the rest of the material. If you really want a complete duck (no bass when kick hits), try adding a gate to the compression bus AFTER the SC3, set to a threshold below the uncompressed volume, but above the compressed volume (in my example case, try setting the gate’s threshold to between -20db and +6db would work, depending on how much dynamics your bass track has: to work around your bass track’s dynamics, apply a compressor to the bass track before both the amplifier and the send). Also (though you may already know), if you’re trying to get the half-beat release style common to most house music, get out a calculator and divide 60000 (milliseconds in a minute) by the BPM of the song, then divide that by four. The result is what you should set the release in SC3 to (set the attack to as low as possible). In fact, if you’re really after a heavy duck, do all of the above, but duplicate the kick track, move the region to slightly ahead of the actual kick, and use that track as input 1 in the compressor track (disconnect this track from the master outputs, or it will sound weird). I’ve just done it, and trust me, that is some HEAVY ducking. Works like a charm.

Have fun!

EDIT: @linuxdsp: I love your plugins! any chance of a sidechain compressor from you? More interestingly, I can’t seem to find an expander with sidechain in the linux world, which is one of the main things I miss from using Logic. I often used to use a sidechain gate/expander to emphasize rhythm guitars and bass when the crash hits, but since moving strictly to Linux I’ve had to do these manually with automation, which I end up spending a lot of time on that I didn’t have to previously (when using OSX). If anyone knows of a sidechain expander please let me know!

The point is that the plugin cannot advertise its "extra" inputs as a sidechain, so its not possible for Ardour to "understand" how the plugin should be wired up. This is, just as a footnote, a problem with several other plugin standards too.

You don't put tracks or inputs "in" a send. A send is a routing from a track (or bus) to another bus (or track). You create a send from the bass (why does it have 2 channels?) that connects to the first 2 inputs of 3-input/2-output bus. Then you create another send from the kick to the same bus (but connected to the 3rd input). The bus contains the SC plugin.

I really think that the instructions at are qutte detailed and should get you going. But do feel free to ask again.

Ah, I got it working. However, currently, the bass plays only when my kick plays. I would like to invert this if possible: The kick will hit and the bass comes in as the kick is resolved. How do I go about doing this in the plugin’s settings? I’m using SC3.

Thanks, I appreciate your help.

Kind of surprising that no one knows / is willing to help with what I would think would be a very common function. Anyway, in lieu of this, is there a means of side chainingly EQing a range? For instance, instead of sidechaining the whole sound, merely having a kick’s bass take precedence over any other lows that may be crunching around down there?

My issue is that, I am trying to keep my kick at 0 db to make it really pop. However, when I use compression with a release any faster than 5ms, there is a rather obvious amount of distortion (and I’d prefer to have as low a release time as possible).

So I’d like to find a way to either side chain the sub bass against the kick (which no one responded to above, as when I tried with the SC3 plugin it merely played the sub bass ONLY when the kick hit, I want the exact opposite, I need the kick to clip the sub bass), or side chain/smartEQ cut the lows whenever the kick hits.


EDIT: I am trying to prepare this for play at parties and such, as I am DJing a few upcoming events! That’s why it’s so necessary for me to try to match the sound levels of professional tracks (which stinks because I am totally and utterly new to mastering process).

@Peter7K: perhaps you missed the key point.

There is no plugin API that allows a plugin to mark an audio input as “The SideChain Input”. This means that the host can’t know how to wire up the plugin. This in turn means that its only the user that knows that the third (or second, depending) input of the plugin is a side-chain. So talking about this as a common function is a bit misleading - its certainly a common function, but its one not supported by plugin APIs and thus very hard for hosts to offer as an automatic, easy thing to do. If a plugin API allowed a plugin to say “hey, this input isn’t a normal input, its a sidechain, so please be sure to use it that way” then hosts (like ardour) could make this all much simpler for users. but they don’t.

(note: its possible that VST3 does this. but VST2 and AU and LADSPA and current LV2 do not)


  • Create a new 3-channel bus
  • Add an SC3 to that bus, set Chain balance on the SC3 to 1 and the others to taste
  • Add a send from the kick track to input 1 of the bus
  • Add a send from the bass track to input 2 (and optionally 3) of the bus
  • Make sure the bass track is not connected to any output
  • Hit play
  • Profit!

Thank you for laying it out for me so simply!

I apologize for my incompetence, this really was soo simple haha. Thank you both.

Okay, so I thought I had it… and it kind of looks visually like it is actually being compressed ever so slightly… but it’s nowhere near enough, not really sure what’s up. Here’s what I have, maybe someone can look at this and check out what’s wrong (hopefully everything should transfer over in that file). Thanks.

You have the compressor settings wrong.
Clear all the automation you currently have on the SC track and set all the automation items to Manual.

Set the SC3 compressor to

You can play around with Thresh, Ratio and Gain to get the perfect balance. If you decrease Thresh you have to compensate by increasing Gain

Wawooo! Thanks mate.

I’m curious if someone could help me with the settings for the complete elimination of sound of the thing that is being compressed, much like LMMS’ peak controller side chaining function. Basically the plugin will allow the sound up to 0 dB, and when the kick hits (the kick being 0 dB) the sound that is compressed is TOTALLY eliminated. I’m having a trouble getting more than just part of the sound eliminated with the SC3 plugin. :frowning:

Why does the SC3 (and SC4) have a ratio control labelled 1:n when almost every other compressor in existence expresses compression in terms of n:1 and expansion is normally 1:n? What is ‘chain balance?’ - I mean I could figure it out, but I’ve never seen it (called that) on any other compressor? And why on the SC4 can I adjust the RMS / Peak to something between 0 and 1 e.g. what does RMS / Peak of 0.005 actually mean?

I think the issue is that the ratio only goes up to 10… which is not nearly enough for some real ducking, like one might hear in house music or something like that. I haven’t found a way to stack this compressor either (perhaps if one can’t increase the ratio one might be able to layer the compressor to get more compression?).


You can always take a peek at Steve’s code to see what is actually going on there. As I am sure you know though, even though the labeling isn’t quite standard, as long as it gets the sound desired it becomes secondary(Though it is still an issue and one that should likely be fixed). In this case I think it is pretty obvious what it means no matter what, it certainly has never bothered me much.


Yes! This is much easier… I had been stacking multiple outputs all to the one 1st input in the SC3… a simple amplifier before the send makes much more sense.

It’s still a bit of a hassle… and an expander would be very nice to have. Hopefully Linuxdsp could provide a plugin and/or Ardour3 could facilitate ducking/expanding much better!

@macinnisrr, Peter7K: A sidechain compressor / expander could certainly be added to the (increasingly long) list of things to do in 2011 - there will also be some updates to a few existing plugins due in January too - watch out for a much improved ‘MKII’ version of the graph-eq with some great GUI improvements and some new ‘analogue’ style eq curves - screenshot of the prototype here:


Every day I am closer to switching back to Linux full time for studio work, I really am looking forward to testing out your plugins when I do:)


@linuxdsp: looks great! I’ve been really happy with your pro mx plugins as well as your VC2 and ch-eq2 apps (use them on almost every project); keep up the great work!

Additionally, one thing I personally would pay a good amount of money for would be a sidechain-equalizing plugin (I don’t know if this already exists or not but it seems like it would be EXTREMELY useful for mixing and some desirable effects):

The plugin could act as a sort of look-ahead limiter and limit/certain frequencies that are the same as the compressing sound, the end goal would be to have (when the plugin is active) a waveform of exactly the same dB at the end.

For instance, if you have, say, a bass line and a kick, let’s say (just for this example) that the kick ranges frequencies 20Hz - 80Hz, and the bass encompasses 60Hz - 200Hz. When the kick would hit, the bass’ sound would be compressed, but ONLY in the range of 60Hz - 80Hz (of course the plugin could allow for limiting, or completely eliminating the bass’ sound in the 60Hz - 80Hz frequency, or just compression and merely decreasing the volume of that frequency range).

I would probably pay upwards of $40 for a plugin with this functionality.