In this article we look at some of the common, and less common modulation effects, examine what they are and why and how they sound the way they do.
Anyone who has ever heard a choir, string section or any ensemble perform live will understand how impressive the richness of multiple people playing the same thing is, and it is trying to recreate this thick, lush sound which lies at the root of modulation effects. They might have diversified over time and the artefacts which gave them away as not being the real thing are now valued as part of the charm, but ever since we could make sounds go woosh and swoosh we’ve been thickening up our sounds using modulation. There are many ways to add movement and interest to sounds. In this article we look closer at modulation effects.
To Illustrate all of these effects we have an example using the following guitar recording, we chose this distorted guitar sound as the harmonic content makes the effects easy to discern.
The three most common modulation effects, Chorus, Flanging and Phasing are all created using a modulated delay. A standard digital delay which has its delay time modulated by a low frequency oscillator (LFO) can create all of these effects, the only difference is in the specific delay and modulation settings. It’s important to note that these effects rely on the difference between the modulated signal and its dry, unaffected original. The effects are only properly audible if mixed in with the original.
Chorus
Starting with chorus, this technique involves the duplication of an audio signal, wherein each copy undergoes a variation in its periodicity or pitch. These modulated duplicates are then blended with the original signal. A chorus effect can be made with a single delay but the cyclic nature of the effect becomes predictable to the listener. Adding more delays at different speeds and depths adds more richness and disguises the cyclic nature of the effect.
Chorus employs longer delay times typically with delay times ranging from 15 to 35 milliseconds proving most effective compared to the likes of phasers and flangers, which means that there is less of a ‘comb filtering’ sound to the effect. Slow modulation speeds are common, with faster speeds making the pitch modulation more noticeable and the faster effect adding a nervy edge to the sound.
Chorus was such an over-used effect in the 80s that I’m only just getting over it! When used tastefully it can thicken up sounds in a pleasing way, though when over-used things can sound indistinct and washed out. Chorus is a great way to place a sonic nod to the 80s, especially if you drown it in reverb too!
Recommended Plugin - Arturia Dimension-D
Flanging
Best explained to someone who doesn’t know what a flanger is by referencing the intro to Heart’s Barracuda (Or Rush’s Spirit Of The Radio), flanging produces a distinctive sweeping sound by introducing a slight delay to one of two identical audio signals while modulating the delay time. This creates constructive and destructive interference between the signals, resulting in a jet-like effect. Similar to chorus, the key difference is the shortness of the delay time, short enough for the signals to comb filter aggressively. Whereas Chorus is principally intended to subtly flatter Flanging is more attention-grabbing, though used with care it can still be subtle.
Recommended Plugin - Eventide Instant Flanger Mk II
Phasing
There are some confusing twists of terminology associated with the history of modulation. A perrenial source of confusion is between flanging and phasing. These days flanger is commonly taken to refer to an electronic device but the term was famously coined by John Lennon when referring to the practice of modulating the speed of a pair of tape machines playing back the same audio by manipulating the reels or ‘flanges’ of the tapes. Confusingly this technique is also known as tape phasing. Check out Luke’s demonstration of how to do authentic tape flanging below.
The two terms settled out into distinct techniques when they became purely electronic processes. As already referred to above, the flanger came into being with Eventide’s delay lines. The signal can be manipulated easily in the delay line, but the delay applied to the signal is uniform across the entire spectrum.
Phasing involves splitting an audio signal into two paths, altering the phase of one path, and then recombining them. This creates peaks and notches in the frequency spectrum, resulting in a swirling, psychedelic sound. this sound very like flanging but a key difference is how these effects were produced. Analogue phasers used all pass filters, which have a non-linear frequency phase response. This means that different phase rotations are applied by the filter at different frequencies. Most phasers use multiple “stages” adding additional all pass filters to rotate the phase more dramatically. The key difference is that the effect varies with frequency in a phaser.
Recommended Plugin - Softube Fix Phaser
Tremolo
Tremolo is a modulation effect that rhythmically varies the volume of an audio signal. It has been available as an effect on some guitar amplifiers for many decades and as such can be very evocative of 60s Americana. As well as the rate of the amplitude modulation, the shape and depth is also very important and the best tremolo plugins offer extensive control over the shape of the LFO. Just drawing in square wave volume automation won’t sound right.
One notable, and unusual variation of tremolo is harmonic tremolo, often associated with vintage Fender amplifiers. Harmonic Tremolo differs from traditional tremolo by modulating the amplitude of the high and low frequency bands independently, as opposed to the overall signal. This approach results in a more interesting tremolo effect than mono tremolo. Deep mono tremolo makes the sound pulse on and off, harmonic tremolo is always passing audio, as is the more common stereo tremolo, which to all intents and purposes is the same as autopanning.
Very common on electric pianos, along with the previously mentioned phaser, tremolo is rather overlooked, which is a pity as it’s a lovely effect, though rhythmic gating effects can be seen as a modern, more sophisticated equivalent to tremolo. The strict rhythm of gating effects is addictive but there’s something nice about a free-running tremolo which isn’t directly tied to the tempo of the music.
Recommended Plugin - Goodherz Trem Control
Vibrato
Vibrato effects are relatively unusual, which is interesting because real vibrato is so universal to instruments which are capable of it. Vibrato is of course a modulation effect that introduces periodic variations in pitch, creating a pleasing effect which should ideally be the right speed and depth. Going outside of the typical variation of somewhere around a quarter tone and in the region of 6Hz never sounds quite right. Famously the tremolo arm on electric guitars was misnamed, as it modulates pitch, the ‘vibrato arm’ has never broken through though!
As stated earlier vibrato is rather unusual as an audio effect but one place where the mechanical sound of artificial vibrato really works is in organs. Hammonds had a chorus/vibrato section but the organ I really associate with vibrato has to be the Vox Continental. You might see ‘vibrato’ controls on some guitar amplifiers but these are likely to be misnamed tremolo effects! The Boss CE-1 chorus pedal has a genuine vibrato effect and there are various plugin versions of this available, Avid make one available in the bundle of stomps which were originally developed for the Eleven Rack.
Recommended Plugin - Avid C1 Chorus-Vibrato
Frequency Shifting
Frequency Shifting is an odd effect, I first came across it in my teens when a friend had an old frequency shift guitar pedal pedal from the 70s. We really didn’t know what to make of it…
Frequency shifting isn’t the same as pitch shifting. Pitch shift maintains the harmonic relationship between frequencies. Frequency shifting does not. As a result the effect tends to be unmusical. Like its relative the ring modulator it is a good source of clanging, clashing tones. As already mentioned unlike pitch-shifters, frequency shifters do not aim to maintain the harmonic relationships of the original audio. Instead, when the pitch is adjusted upwards or downwards harmonics are offset by a fixed amount, which usually takes it outside the harmonic series. The resulting sound often takes on an eerie metallic or bell-like quality that deviates significantly from its original form. This sounds like a digital process and while this is easy to achieve in the digital domain, just like ring modulation, frequency shifting can be achieved using analogue components.
Because it doesn’t maintain the harmonic series it’s most successfully deployed on unpitched sounds like drums and percussion or reserved for special effects. If you want to try frequency shifting effects check your stock plugins as you might already have one. For example Logic Pro’s Ringshifter plugin combines ring modulation and frequency shifting.
Recommended Plugin - Melda MTransformer
Leslie
Renowned for its distinctive swirling effect, the Leslie speaker has become synonymous with vintage and classic tones. Originally invented in the 1940s by Donald Leslie, the defining characteristic of the Leslie speaker lies in its rotating components. By incorporating a spinning horn for the top end and a rotating baffle on the woofer.
The interesting things about the Leslie, which is de rigeur on hammond organs but has also seen use on guitar, vocals and electric and acoustic pianos on many classic tracks, is that it combines elements of several of these modulation effects. the amplitude modulation of tremolo, vibrato introduced by doppler shift and complex phase interactions due to the changing interactions of the drivers with the room. Check out Luke’s article 5 Leslie Speaker Sounds On Record for a tour of famous Leslie examples on record.
Despite the advent of digital emulations and advanced software plugins, the unmistakable charm of the original Leslie speaker remains unmatched. However some excellent emulations do exist as audio plugins.
Recommended Plugin - Universal Audio Waterfall Rotary Speaker
Traditional modulation effects, such as chorus, flanger, and phaser, were born out of the possibilities offered by analogue technology. These effects relied on the manipulation of voltage-controlled components to create cyclical changes in sound. However, with the advent of digital audio workstations, the landscape of modulation has expanded exponentially. In a DAW, any parameter can be changed cyclically, emulating the rhythmic patterns produced by LFOs traditionally found in hardware units.
Through use of of automation, producers and engineers can modulate parameters like frequency, depth, and delay time over time, opening up a world of creative possibilities. Whether it’s creating evolving textures or animating synths, the flexibility offered by DAW automation allows for intricate and precise control over modulation effects. The limitations of analogue technology may have been transcended, but these traditional effects are familiar and often reference particular genres and periods of recorded music.
What is your approach to using modulation effects?