Harmonic Tremolo is a variation on the more familiar tremolo effect we’re used to in that rather than varying the amplitude of the entire frequency spectrum it splits the spectrum into two bands and varies the level of each in opposition with each other - so when the level of the bass rises the level of the treble falls and vice versa, all in a cyclic, repeating way to give a more interesting version of the familiar tremolo “wobble”.
This effect has been around for a long time, it is well known as a feature of some old Fender guitar amps and there are guitar pedals and a handful of plug-ins which recreate this effect. Trem Control from Goodhertz and Tube Modulator from Audority both offer a harmonic tremolo mode but for such a simple effect I thought I would be able to create something which was similar using stock Pro Tools plugins.
Using Stock Pro Tools Plugins To Create Harmonic Tremolo
This turned out to be much harder than I had anticipated. Of course, an effect like this could be created using automation. The pencil tool offers a way to quickly automate a pair of filters using the triangle setting, though creating an inverted version of the automation is a little awkward. But I wanted to create a harmonic tremolo effect using just plug-ins.
There is no dedicated tremolo plug-in in Pro Tools even in the Eleven effects, I’ve always considered this something of an omission. There are amp models in the Eleven MkII and Eleven Lite plug-ins, which feature tremolo but this is strictly speed and depth, with no way of splitting bands. I considered trying to use two amps with identical settings on duplicate paths with a high and a low pass filter on each but the issue I hit over and over again when trying to “cheat” this effect was how to create a second tremolo which runs at the same speed as the first but in the opposite direction. I considered using a delay to offset one against the other but that would be delaying the audio path as well as the modulation.
I descended further and further into increasingly impractical ways to get this effect. Using the tremolo output from an amp sim not in the audio path but feeding the sidechain of an Avid Pro Multiband Dynamics with two active bands one of which was set to attenuate its band the other of which was set to boost provided the correct process but actually using it was horribly convoluted.
How Did I Create Harmonic Tremolo using Stock Pro Tools Plug-ins?
In the end, I did manage to make an effect which was close to the effect I was after, by using two AIR Filter Gates, one running at 1/4 notes, the other running an offbeat 1/8 note pattern. that way I was able to get the synced but opposite modulation I needed. It wasn’t perfect but it was a really interesting journey.
Using 3rd party plug-ins, I already had, I was able to create a much better effect using Exponential Audio’s Excalibur, which because it allows the phase a common modulation source to be offset at different modulation destinations the effect was simple to set up.