Low Frequency Oscillators: Create motion with a single press


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What is an LFO?

LFO stands for Low Frequency Oscillator. It's a term you've probably heard relating to synthesisers or audio effects. The LFO takes a particular setting or parameter and applies back-and-forth movement to it (oscillation) at a low frequency - that is, a speed slow enough that you can easily hear the changes it's making.

For example I might apply this movement to the detune knob of a synthesiser which would allow the detune knob to have some movement added to it. You would audibly hear the detune amount changing as if someone was turning the knob.

How can I use an LFO with a MIDI controller?

An LFO does not make sound by itself. It is simply a modifier placed on top of another setting. This is a perfect scenario for MIDI control. MIDI itself, after all, is a digital message that ends up controlling something else.

Think of the LFO as a "third hand" which can add movement to a MIDI value for you instead of doing it manually. For example, say you have an expression pedal that you use with your BRIDGE6 or BRIDGE4 to send a MIDI CC message to your Line6 HX Stomp. It controls the Tremolo Depth because you like to vary the depth throughout a particular song section for a fun effect. But now you want to control something else instead. You could add the Tremolo Depth CC message to a MIDI LFO and have it slowly oscillate the depth, and free up your expression pedal (and your foot and your brain) for some other effect like Wah or Volume.

How do the LFOs work on the BRIDGE6 & BRIDGE4?

On our BRIDGE controllers, every switch on every bank is able to apply an LFO to the messages in a single chosen message stack. That's 600 LFOs on a BRIDGE6 and 400 LFOs on a BRIDGE4!

Each LFO has its own settings and can be synced to one of the two MIDI clocks onboard, or be free-running with a custom frequency from 0.1-10 Hz. You can choose the waveform, trigger type, minimum and maximum value/velocity limits, and the step size to create a completely different effect for each LFO.

Any MIDI messages that are in the selected message stack (i.e. Toggle On, Toggle Off, Press, Release, Hold, Hold Release, or Double Press) will be sent at the frequency you choose (from min to max 0.1-10 times per second) with the value changed for each message, within the limits you set, and with the step size you set.

The Trigger determines whether you want to LFO to work only while you hold down the switch, or whether you want the switch to act as an on/off toggle.

Clear as mud? Let me show you.

The LFO is set to 1hz with the minimum value set to 0 and the maximum value set to 127. That means that every second, the value will be moved from 0 to 127 and back to 0 again. The Step size will tell us the value intervals. If it's set to one, then we will get 127 messages sent in one second (val 0,1,2,3,4,5,6,7,8,9...127), but if the step size is 32, only 4 messages will be sent per second (val 0,32,64,96,127)

This cycle will repeat as long as the LFO is active, cycling from minimum value to maximum value. The "Reset" LFO setting will determine whether the LFO starts from the minimum value every time the LFO is stopped and started again, or whether it picks up where it left off.

The Screenshot below shows the really fast MIDI data (note the time on the far left) and the CC value increasing in steps of 1

Notice the multiple 1's at the start? That's because of the sine wave - it starts slowly so it stays on "1" for a bit longer then speeds up by the time it gets to "8"


One thing we haven't mentioned yet are the waveforms. The way the MIDI data is sent out can be changed. Think back to our illustration of turning a knob on a pedal: if you want to turn the knob from 0% to 100% and back to 0% in 3 seconds, you can do that lots of ways. You could turn it very slowly to start with, and then turn it back very quickly right at the end, or you could turn it smoothly the whole time from 0% to 100%. This if what different waveforms do in an LFO. They change the speed that the data is changed at different point in the cycle.

On our BRIDGE controllers there are 6 waveforms:

  • Random
  • Ramp
  • Sine
  • Square
  • Triangle
  • Sawtooth

Here is a chart showing how they module the data

Time to Experiment!

Now that you understand how the LFO works, you can start automating parameters on your MIDI-controllable software, hardware, effects, apps and more!

Wanted a phaser on your HX Stomp, but don't have enough blocks? Why not use that EQ block you've got in there already and automate one of the bands with the MIDI LFO? problem solved!

Need a really weird sound for an ambient guitar track? Why not assign and LFO to the mix knob on your reverb pedal?

The possibilities really are endless. We can't wait to see what you create.

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