LFO: It’s just an oscillator…


When it comes to digital audio environments then every one of them will probably know some kind of breakthrough or big development along the way. Max becoming part of Ableton Live as Max for Live would be a good example. But often big things can appear to be quite small. When looking at Native Instruments; releasing their free players and a trimmed down version of Komplete may not seem like a very big deal, but I think the impact it had most certainly was!

And sometimes big “trouble” comes in small packages and that’s where things can get interesting. Take Reason’s Pulsar rack extension. Its free (until the 1st of October 2012), its a twofold LFO device and well. It’s just an oscillator, right?  Hmm, yes and no 😉


It stands for Low Frequency Oscillator and its actually part of most synthesizers and DAW’s in general. However I get the impression that many people can’t really imagine anymore what an LFO actually is, does or can do. After all, in most environments its a separate section which can often be used to control parameters in other sections, and make them wobble 😉

An LFO device as can be found in Guitar Rig 5

But quite frankly there’s much more to an LFO than that even though its essence is actually very simple: it’s an oscillator which generates a very low pulse, often a sine wave. Its actually so slow that we can’t even hear it. And that’s where it can get interesting because just because we can’t hear it doesn’t mean its not there…

Wibble Wobble

An LFO is most often used to create some kind of tremolo, or wobble, in your sound but using it to influence other parameters has also become quite popular. For example; when looking at the Guitar Rig LFO device above then you’ll notice the white “LFO” section at the top left corner. That can be dragged onto any other control in the Guitar Rig effects rack. Whatever its dragged onto will then be controlled by the LFO device.

It’s actually quite common to have an LFO controlling device these days. Take for example this Max for Live LFO controller on the left. The section at the right side of the device can be used to point it to some device parameter, regardless on which track this device has been placed.

After the connection has been made this patch can then modulate the parameter and change its value in a way which is fully programmable by the rest of the interface.

Pulsar Dual LFO

Pulsar is Reason’s implementation of a separate LFO controller. It has two LFO devices which can even influence each other, and it has an envelope section which gives even more control over the way the LFO’s can behave.

The LFO’s can be used “in sync” so that they follow the overall beat / speed of your project, but of course you can also use them as a totally independent source. And as could be expected from a Reason device; it provides a lot of CV in- and output connectors which allows for full control over the LFO’s but also provides the LFO’s a means of control over other device (if those can use input CV signals of course).

Apart from CV connections the Pulsar device also provides several audio-out connectors, and here things start to get interesting…

Mono synth

A Sine wave signal, produced by Pulsar.

As can be seen in this screenshot of my M4LScope Pulsar can generate audible frequencies, as such you can use it as a sound generator. Better yet: because Pulsar has a keyboard follow knob it can track the incoming MIDI data and change the LFO’s frequency accordingly, this allows you to use Pulsar as a mono synth.

But because Pulsar can output audio signals there’s much more you can do…

Amplitude modulation

Lets say you’re working with a Reason song which contains 16 tracks and you want to apply a wobble to your overall sound score, how would you proceed?

I suppose you could try to setup two 14:2 mixing devices and chain them, after which you connect a Pulsar LFO to every available channel’s level CV input so that you can modulate the outgoing audio level. However, things can be setup much easier than that:

Using one Pulsar to effect a whole sound.

You can click on the picture to get the full sized screenshot.

While you can use the Pulsar’s CV outputs to control other Reason devices, you can also use its audio output to apply so called amplitude modulation on an audio signal, such as an entire music score.

When you set the Pulsar to very low frequencies you most likely won’t hear any sound, especially if you’re using sine waves. But as I hinted at somewhat earlier: just because we can’t hear it doesn’t mean it isn’t there.

As you can see in the screenshot the led output of the line mixer reacts even though no note is played on the keyboard (check the ‘note on’ indicator on Thor if you don’t believe me). That’s because its reacting to the signal as its being sent out by Pulsar.

And if we bring that low frequency signal together with a full music score you’ll notice that the entire sound spectrum will be affected by it; generating a global wobble in the sound. So in my example above: if I play my Thor pad it will result in a pulsating sound. That’s because I combined my Thor sound with that of the Pulsar LFO.

This is caused by amplitude modulation; we’re basically adding one sound signal to the other. And because one signal is a “wobble” this will eventually apply to the entire sound itself.

And this is one of the reasons why I favour Pulsar so much. While it may appear to be very straightforward and relatively ‘easy’ you can actually do many crazy things with it. And never underestimate the things you can do with a tone generator, if you want more proof of that you should look into the stuff the tone generating module can do within the Kong drum designer.

Using sound to display sound effects

Now, this is something I’ll be diving deeper into in an upcoming post but just to give you a little preview demonstration…  Maybe you’ve heard of the Polar rack extension; a harmonizer and dual pitch shifter effect. I always like to experiment with such effects by sending a rather sub standard sound into it and check the results.

With such studies you’ll often learn a whole lot more about the effect and the things it can do. And because Pulsar can also be used as a mono synth, or tone generator, that makes it the ideal tool for the job.

A simple square wave generated by Pulsar.

Here you can see a rather standard square wave which I generated using the Pulsar rack extension. Just for fun, this is what it looks like when I turn the shuffle knob:

A shuffled square wave generated by Pulsar.

As you can see it does everything which the Propellerheads promised us; by applying so called pulse width modulation it actually changes the tone and appearance of the sound quite specifically.

Now, what would happen if I take the first (standard) square wave and feed it into a Polar?

A simple square wave generated by Pulsar and processed by Polar.

As you can see the square wave itself changed a bit; it now shows quite a bit of extra wobble, but that by itself isn’t the big deal here. The big impact is on the harmony of the sound, and you can see as much in the middle which shows you the interaction, or harmony, between the two sound signals (left and right combined).

Speaking of the wobble in the square waves… If you check out this blog post in which I theorize a little about how different DAW’s can expand but also impact each other you’ll see that a lot of “aliased sound sources” come with a lot of wobble on their own.


I think its a good thing to see Reason finally getting a little more tools which people using other environments have gotten their hands on long ago.

But I think its very refreshing to see that the Propellerheads haven’t lost their touch when it comes to their own instruments and effects. Its why I favour their material so much and also the reason why the only expansions I want to get my hands on are the ones from the Propellerheads themselves.

That is, everything except the radial piano; I simply have too much piano sounds sitting in my gear already.

And there you have it, hope you enjoyed this post.