How does a vocoder work?

Although they were originally developed in the 1920s for communications purposes, vocoders found a niche within electronic music as an instrument for creating “robotic” vocal sounds.

In modern popular music, vocoded sounds remain as popular as ever – for example, you’ve heard them on Zedd, Maren Morris, and Grey’s “The Middle” and Ginuwine’s “Pony.” But it can be difficult to understand exactly how a vocoder modifies your audio. In this post, we’ll take a look at what exactly a vocoder does. We’ll then apply this knowledge to help us use some common vocoder parameters to their fullest.

What’s better than one signal? Two.

Vocoders require two audio sources: a carrier, which acts as the initial sound source, and a modulator, whose harmonic characteristics shape the sound of the carrier. This is achieved through the use of a “filter bank,” which analyzes the modulator signal, divides it into frequency bands, and applies a band-pass filter to each one. The filters are tuned automatically to the center frequency of each band present in the modulator signal. Finally, once the carrier signal is sent through the filters, the vocoder raises or lowers the level of each filter according to the harmonics of the modulator signal.

Carrier and modulator signals can be difficult to grasp, so think about how the sound of your voice works for a simplified analogy. Your lungs produce air, vibrating your vocal cords; this is a carrier signal. Next, the rest of your vocal tract shapes the vibrating air as it leaves your body. A vocoder works in the same way, by affecting the carrier signal according to the characteristics of the modulator signal.

What kinds of signals can I use?

Any type of audio signal can be used as either a carrier or modulator (or both simultaneously), but music producers typically use synthesized sounds as carriers and vocals as modulators. For a classic example of a vocoder effect using a saw wave patch as a carrier and a spoken human voice as the modulator, listen to 1:16 of Kraftwerk’s “Trans-Europe Express.”

For a demonstration of a more scratchy, experimental vocoder effect, check out our recreation of Kavinsky’s “Nightcall.” This Vocalsynth 2 patch consists of two square waves playing chords and some white noise that serves as the carrier, which is modulated by a spoken vocal part.

How do I make my vocoder sound good?

To get great results from your experimentation with vocoders, you’ll probably want to use a carrier wave that is rich in harmonic content. If you provide the vocoder with more harmonics, the modulation effects will be much more evident and intelligible than, say, a sine or triangle wave. We’d recommend beginning with a saw wave or saw-based synth patch. It’s also not a bad idea to compress and / or saturate your carrier signal on its way into the vocoder; a more limited dynamic range will help accentuate the effects of the filter bank.

Now let’s talk about the modulator. When you’re singing or talking into a vocoder, don’t be afraid to over-articulate. Pronounce the words more clearly than you usually would; since the harmonic characteristics of your voice will be very different, your diction is key to an intelligible vocoder effect (assuming that’s what you’re going for). Pitch doesn’t really matter when singing into a vocoder, so focus on making the other characteristics of your voice as interesting as possible.

What are a vocoder’s parameters?

Here are a few parameters commonly found on vocoder plugins and hardware that can help guide your creative process:

Bands

This refers to the number of frequency bands into which the modulator signal is split. Essentially, you can think of this as resolution. Vintage vocoders tended to have fewer frequency bands, so try using a setting of 8 – 12 bands for a more classic sound.

Frequency range

This refers to the upper and lower limits of the frequency in the carrier signal accepted by the vocoder. To increase intelligibility, try raising the upper limit of the frequency range on your vocoder above ~5 kHz.

Formant

Some vocoders offer a formant parameter (sometimes also referred to as “shift”). This will increase or decrease the frequencies of the filters, which makes the result sound brighter or deeper, respectively. These are great for blurring the lines or switch between “male” and “female”-sounding vocals. In fact, some vocoders even have a “gender” parameter dedicated to this!

Unvoiced

Unvoiced sounds occur naturally in human speech. Also known as plosives, these sounds are produced when we make a consonant that requires blowing air through the lips, such as “p” or “b.” Many digital vocoders are capable of detecting these airy, noisy sounds, which span a distinct frequency range from pitched, vibrating vocal cord sounds. For example, on Ableton’s Vocoder audio effect, the Unvoiced knob allows the user to mix a noise generator in with the carrier wave to ensure that these unpitched transient sounds remain present in your vocoded audio.

Do you have any questions on how to use vocoders? Are there any vocoder tricks that you rely on in your own productions? Let us know in the comments below.

July 23, 2019

Max Rewak Max Rewak is a record producer, audio engineer, and music writer, based in New York and currently working in Sounds content at Splice.