Here’s a great tutorial on how LFO’s work on a synthesizer and how to use them with your synths.

I’ll run through a few real world examples of what we can use LFOs for and how we go about setting them up. I’ll be using a few different synths in my screenshots and audio but you can use any synth with an LFO that can be routed freely.

Step 1: Simple Auto Panners

If you are new to LFOs or they mystify you slightly, it’s best to start simple. I find one of the best ways to demonstrate an LFO in action is set up a basic auto-panner effect. The aim of the game here is to use a free running, sine wave based LFO to control the master pan setting of your synth.For those of you who are totally in the dark here and have no idea what an LFO is, let me give you a very brief explanation. LFO stands for “Low Frequency Oscillator”.

Now although these are oscillators they don’t actually make any sound, so try not to associate them with the regular sound generation oscillators in your instruments.Instead try to think of LFOs in a similar way to envelopes. They are simply a modulation tool and are there to alter other parameters in your synth.

LFOs run at much slower speeds than sound generating oscillators and this is ideal for creating modulation effects in your patches.Your synth’s LFOs will usually feature a number of waveforms to select and depending on the complexity of your synth, a list of routing options to patch the output to your chosen destination. These features will vary from synth to synth of course.

Synthesizer LFO Tutorial - Learning How to Use Your Synth's LFOs

Here you can see that I have used Logic’s ES2 synth and have patched a simple sine wave based LFO to the master pan control using the mod matrix. I also changed the speed of the basic pan effect to make it more pronounced.

Synthesizer LFO Tutorial - Learning How to Use Your Synth's LFOs

Step 2: Vibrato and Other Pitch Mods

Another simple effect that is easily created using LFOs is Vibrato. Essentially this is just pitch modulation and works in much the same way as our earlier pan effect. The only real difference is that we are effecting the pitch of the oscillators in place of the pan.Generally speaking a fast LFO speed coupled with low intensity will produce an excellent and playable Vibrato effect. You can of course experiment with more intense settings and slower speeds, these effects quickly move away from the traditional and into the experimental.

Synthesizer LFO Tutorial - Learning How to Use Your Synth's LFOs

Step 3: Filter Sweeps and Other Effects

When you are ready to get a little more adventurous with your modulations you can start to point the LFO on the direction of your synth’s filter section. Anything from long dramatic sweeps to intricate wobbles can be created here using the same techniques we have covered in the previous sections.If you want to experiment with some more interested effects then you will need to move away from the simple sine wave wave shape we have been using up until now and switch to square and ramp flavours.These new wave shapes will allow you to create new and interesting effects such as the laser style synth effect below and fast stuttering patches. Add some resonance to the mix and you can really make things interesting.

Step 4: Random Action

One of the most under used LFO modes is the random waveform. This can be a great way of creating completely unpredictable but very useable effects patches. Used in a subtle way it can also add a great new dimension to your more traditional patches.Some synths even have a stepped and smooth random wave shape feature, try experimenting with the two but I personally prefer the precise sound of the stepped wave form. Using this shape in conjunction with a resonant filter classic ‘sample and hold’ effects can be created, very simulate to those in the classic tune ‘Rez’ by Underworld.

Synthesizer LFO Tutorial - Learning How to Use Your Synth's LFOs

Step 5: That Syncing Feeling

Although many of the LFO effects we have looked at can be easily created using a free running LFO speed, sometimes you will want the effects produced to be perfectly timed with your project’s BPM.The vast majority of synths offer the ability to tempo sync their LFO’s speed at the flick of a switch. Once this feature is activated you should see the speed display switch to musical measures. Any of the effects we have looked at can then be easily timed.

Original source: http://audio.tutsplus.com/tutorials/production/practical-tips-for-using-lfos/