Tremolo, sure you know what it is and what it does (it makes that “whoa whoa whoa whoa whoa”
sound), but do you know HOW it does this? Somebody just figured out how to take the sound a Floyd Rose makes and put it into a circuit, right? Simple! Errr… no. I suppose another research project would be figuring out how Floyd Rose and others started using the term “tremolo” for their products, but it’s a very inaccurate term. Think about it for a bit, when you shake the whammy bar on your guitar, does it sound remotely similar to a Fulltone Supa Trem? That’s because the two devices are doing completely different things to your sound. The tremolo (pedal/effect) is manipulating volume, while the tremolo (tailpiece) is manipulating pitch. The tailpiece part of that should be pretty obvious, which means all those goofy folks that insist on calling your bridge a “vibrato” are 100% correct in their terminology. So one last time, tremolo is volume, vibrato is pitch. Got it? Cool, let’s dig deeper.
How it works
So how does a tremolo pedal work? Probably the most common and simplest (with modern technology) is to modulate input voltage via circuit. This is how your typical Boss tremolo works. In this scenario, a voltage controlled amplifier (VCA) adjusts signal amplitude with a specific waveform to create the tremolo sound. (Don’t worry, I’ll explain the waveform options below) These tremolo pedals often sound nice and work reliably, but similar to listening to vinyl, there are many people who prefer some of the imperfections of other technology.
Other types of tremolo technology involves a low-frequency oscillator, which feeds the signal back into the amp in-phase, causing a tremolo sound. The low-frequency oscillator helps create the tremolo effect by controlling the speed and as far as I know, only produces a sine wave.
Expanding on that technology, some tremolos use the low-frequency oscillator combined with high and low pass filters. This is how many older Fender tremolos work as well as the Catalinbread Pareidolia Harmonic Mesmerizer tremolo.
Next up, tube bias. With this tremolo, the low-frequency oscillator is controlling the power tube bias. Essentially acting as a dimming switch for the bias that goes up and down, resulting in a nice tremolo effect.
Back in the glorious 60’s, the same process was also adapted with a light bulb. This is called a photocell tremolo and involved the low-frequency oscillator modulating input level. With this technology, the bulb would turn completely off and on, which created an effect more like a square wave. Which brings me to…
For the purpose of this fairly basic article, we’ll focus on three waveform patterns; square, sine and triangle. Forgive the imperfect drawing below, but it gives you a very good example of what a tremolo is doing to the input signal.
Square wave – this is how a digital sound wave is represented. The up/down pattern depicts the on/off nature of digital. In a tremolo, it’s the very hard tremolo sound where you can hear the signal go completely silent during oscillations.
Sine wave – the traditional tremolo effect. The sound is a fairly smooth up/down pattern similar to moving your volume knob up and down. This is an analog sound wave, but digital devices can replicate the effect to varying degrees of effectiveness.
Triangle wave – kind of a hybrid in the sense that it has a smoother effect like a sine wave but cuts quickly. Square and triangle waves have only odd harmonics, which gives them similar characteristics.