Although chorus, flanger, and phase-shifter are very similar, there are a few major differences in how those effects actually work. Similarly to the chorus, the flanger creates a copy of the original signal and applies a delay and a comb-filtering to it. Chorus uses much longer delay times and, instead of comb filtering, applies pitch modulation. Phase-shifter does not use a delay on the copied signal but instead applies a series of all-pass filters. Out of three effects, the chorus sounds the most subtle, and the flanger is the most extreme.
Now let’s take a closer look.
The difference between chorus, flanger, and phaser explained
To understand better the difference between modulation effects, we have to take a little detour into the realm of science. So if you do not like to be bothered with scientific knowledge or just do not feel like it this time, feel free to skip the next paragraph. If you decided to stick around, you should know that all modulation effects are based on the idea of changing the phase of the signal one way or the other. So let’s figure out what that actually means.
As we all already know, the sound is a wave, and as any wave, it has the highest point of positive amplitude and the lowest point of negative amplitude. If we have two sound waves with the same frequency content interact with each other, depending on how those points overlap, we will have different results of the interaction.
If the points of the highest positive amplitude of both sound waves overlap perfectly, the sound would be considered “in phase”. This will result in a much stronger and louder signal. When the point of the highest amplitude of the one soundwave overlaps with the point of the lowest negative amplitude of the other soundwave it is called an “out-of-phase” sound. Overlapping frequencies will cancel each other out, and this will result in complete silence.
Some interesting results could be achieved if you have very complex soundwaves and apply some time variation into their interaction. This will result in a different frequency band overlapping at different times. Which, in turn, will make the sound to be perceived as something spacious thanks to the added sense of movement. And exactly on this proposition modulation effects were designed.
To achieve the chorus effect, one or a few copies of the original sound are made. Then the copy is slightly delayed in relation to the original signal. This makes several frequency bands of the original and copied signals to be out of phase and cancel each other out. After, the LFO is applied to the copied signal, which results in a slight change of pitch.
Originally the chorus was designed to emulate the sense of several instruments playing at the same time. Every group of musicians, for example, an orchestra, couldn’t possibly be perfectly aligned. So, even if the orchestra plays exactly the same note at the same time, you still get the sense of volume and can feel the presence of multiple instruments. This is how chorus occurs naturally.
Chorus can be used as a mono effect and a stereo one. The mono instance has only one copy of the original signal. Stereo has two or even more copied signals with different delay settings and pitch variations. To get a better idea of how this effect actually sounds, let’s remember the electric guitar part from Nirvana’s “Come as You Are”.
A flanger is an audio effect that is achieved by copying the original signal and delaying the copied one for a few milliseconds. Optionally the LFO is applied to modulate the delay. Since the delay time is extremely low, there will be a lot of “out-of-phase” frequency bands across all of the frequency spectrum. This effect is called comb-filtering. When LFO is applied, the interference frequencies will constantly change, which will result in a lot of artificial movement according to LFOs settings.
It is believed that the technique of flanging was discovered by Les Paul, one of the most influential and innovative guitarists of the 20th century. The flanger was popularized further by audio engineers who worked on the famous Abbey Roads Studio. By the request of John Lennon himself, they experimented on two identical reel-to-reel machines in order to achieve artificial double tracking. Rumor has it that the term “flanging” was introduced by John Lennon when he heard the resulting effect the first time. The first Beatles song that incorporated the flanger was “Tomorrow Never Knows”.
Similarly to other modulation effects, the phaser uses the copy of the original signal. But this time, this signal is not delayed. Instead, an all-pass filter is applied to the copied signal. Thus the amount of the frequency content stays the same, and the phase is shifted in specific frequency bands. Traditional phasers use a series of all-pass filters that are usually modulated by LFO. Phase-shifting results in a series of out-of-phase notches that are unevenly spaced due to the filtering.
The phase-shifter was largely inspired by the original reel-to-reel flanging effect and is extremely popular with electric guitar players to this day. The first phaser stompbox guitar pedal was UNI-VIBE, introduced in 1968. Soon Jimmy Hendrix incorporated it into his rig and used it extensively. Another noteworthy example of phase-shifter guitar pedals was MXR Phase 90, used on Eddie Van Halen’s instrumental masterpiece “Eruption”. If you want to get more familiar with the sound that phase-shifter produces, pay attention to the drums on Led Zeppelin’s “Kashmir” throughout the whole track.
The actual difference explained
Since by now we know how chorus, flanger, and phase-shifter work, let’s figure out the actual difference between those effects. Essentially all three of those modulation effects copy the original signal and apply the LFO to the copied signal. This is where similarities pretty much end.
Both chorus and flanger delay the copied signal. Chorus uses longer delay times than flanger. Flanger’s delay times are much shorter and vary around 20 milliseconds. Because of this chorus affects the phase of the low-frequency spectrum and flanger applies phase-shifting only to the high-frequency spectrum. Phaser doesn’t implement any delay at all, and because of that, no harmonic content is affected by phase-shifting.
Opposing to phase-shifter, chorus and flanger have rather dramatic effects on harmonics. Out of these three effects, only the chorus implements the pitch modulation.
Which modulation effect to use
Although there’re a lot of similarities in the sound that could be achieved with those three modulation effects, all of them are quite distinguishable and could be implemented in various ways. Of course, how to use modulation is strictly up to you and your creativity, but generally, modulation more often than not is applied to electric guitars, keyboards, and various synthesizers. Rarely you hear those effects on lead vocals. Dave Grohl of Foo Fighters often uses reel-to-reel tape flanging on his vocal parts.
Out of the three, a chorus produces the most gentle effect and can be used to add some subtle movement and depth to the track. Although you can turn it up to sound quite extreme, usually chorus is applied with moderation.
Flanger arguably is not a very subtle effect because it affects mostly the higher frequencies, which we are more susceptible to. Due to its obvious sound, it is recommended to use flanger on various transition effects in your mix. That being said, flanger could be blended subtly and thus used quite similarly to chorus. After all, the aforementioned Dave Grohl does exactly that.
In terms of intensity, a phase-shifter stands exactly between chorus and flanger. It is not as obvious as flanger and lacks the subtlety of a chorus. Because the harmonic contents are left untouched, phase-shifter sounds rather spectacular on acoustic guitars and drums.
The important thing to remember is that music should come from the heart. It’s a concept that we rather feel than understand. So what modulation effect to use and when is strictly up to you. It is essential to learn the experience of people who have done this before, but it’s more important to make your own impact on the world of music. So you are definitely encouraged to experiment with modulation effects further.