Audio: What Are Faders? (Mixers, Graphic EQ & More)

Faders are perhaps the most important tool for mixing and are often taken for granted. If you're interested in learning more about these fundamental controls in the world of audio, you've come to the right place!

In this article, we'll discuss faders in greater detail, comparing them to knobs and considering their usage across both analog and digital audio equipment.

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What Is A Fader?

A fader is a physical control (or a virtual representation thereof) that slides along a track/slot. In analog audio, a fader is typically designed as a physical control over a potentiometer or, in other cases, a voltage-controlled amplifier.

A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider (by varying the resistance). In the case of the fader, it's a sliding contact.

Put simply, as the resistance is decreased or increased by the fader potentiometer, more or less current can flow through the connected circuit.

Depending on the design of the audio equipment, this can control a variety of different aspects of the audio signal. Most commonly, though, faders are used to control the audio's overall signal level or “volume”.

At one end of the fader's path, the resistance is practically 0. At the other end, it's practically infinite.

Fader potentiometers are nearly logarithmic across this range. Since decibels measure ratios along a logarithmic scale, they're used for linear measurement along faders.

Typically, analog faders hold a logarithmic relationship for about 60 dB, often spanning a bit above and far below a set “0 dB” point. Below this range, near the bottom of the fader, the resistance becomes so high that the signal becomes negligible (mute, for all intents and purposes).

Other than controlling potentiometers, faders can also be used to control voltage-controlled amplifiers (VCAs).

A VCA is an amplifier that varies its gain depending on a control voltage. In the case of a fader, this control voltage is controlled by a slider.

In mixers, VCAs are used in signal routing and channel strips to control the signal level of one or more audio tracks. Audio signals do not pass through VCA tracks. Rather, VCAs are used to control other tracks.

If you'd like an in-depth discussion on routing, check out my detailed video below:

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Faders Vs. Knobs

Faders and knobs are both physical parts that connect to electric parts, typically used to control potentiometers. While knobs are more common for this purpose across all audio equipment, faders are more common in mixer channels.

The obvious difference is that faders are designed along straight sliders, while knobs are rotary.

A side effect of such design differences is that faders take up more space than knobs (perhaps why knobs are more popular).

As I've suggested, faders are commonplace controls for mixer channels, graphic EQ bands, synthesizers, effects units, and more. Knobs can be found on all this gear and more. They're also often more plentiful on equipment that features both faders and knobs.

Beyond their form factors, knobs and faders are often tasked with the same basic function: altering the value of something. This something is often the variable resistance of a potentiometer, which can then control the amount of current flowing through a piece of analog equipment. Depending on the circuit design, these potentiometers can control a wide variety of effects on the audio, including (but not limited to):

• Volume
• Tone/drive
• EQ gain, centre/corner frequency, Q/slope
• Dynamic processors (including compressors, limiters, expanders, etc.) attack and release time, threshold, ratio and even knee and lookahead.
• Wet/dry control (internal parallel processing)
• Reverb parameters (pre-delay, size, decay, etc.)
• Delay parameters (delay time, feedback)
• Synthesizer parameters

Knobs and faders can both be programmed in digital systems and can be controlled via graphic user interfaces and/or physical interfaces. These faders and knobs can often be programmed to control more than what's possible in analog systems and multiple things at once in the case of macro controls.

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Faders As Potentiometers

As mentioned, in most cases, faders act as physical (or virtual) slider controls over a potentiometer.

By varying the resistance/impedance at certain points within audio circuits, these potentiometer faders can achieve a wide variety of results.

The most common, of course, is signal level or “volume” control. This is the case with channel faders in mixers but also applies to individual frequency bands in graphic-style EQs, individual oscillators in synthesizers and effects, and more.

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Faders As Voltage-Controlled Amplifiers

I'll reiterate that faders are also commonly used to send control voltages to voltage-controlled amplifiers. In this case, the VCA acts to amplify and/or attenuate any number of audio channels it's set to control. The fader sends the control voltage to the VCA in order to control such amplification/attenuation.

VCA tracks do not pass any audio but rather act as a control. They allow us volume control over multiple tracks with a single fader, helping simplify our mixing endeavours while maintaining the relative balance between the tracks controlled by the VCA.

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Virtual Faders

We are living in the age of digital audio, but much of our processing is based on the days of analog. Virtual faders are the digital equivalent of analog faders, and they perform the same tasks, only digitally.

In other words, there are no potentiometers, control voltages, VCAs, or electrical circuits connected to virtual faders. They instead work in digital systems to provide the same service, only digitally.

You'll find virtual faders in digital audio workstations, audio plugins and virtual instruments. They are programmed to serve the same functions as their analog counterparts.

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The Use Of Faders Outside Of Channel Strips

We know how faders are found in the channel strips of our mixing consoles/mixers, digital audio workstations, and more. They can also be found elsewhere, and pretty much anywhere a knob could do that job (remember that knobs are more popular thanks to their space-saving).

In addition to channel strips, we may also find faders in the following equipment:

• Graphic EQ
• Controllers
• Synthesizers
• Audio effects

Faders In Graphic EQ

Graphic equalization is a style of EQ where predetermined bands are centred around set frequencies with set Q factors that can be either boosted (amplified) or cut (attenuated) via faders. The name comes from the fact that the EQ settings of a graphic EQ unit typically look very obvious and “graphic”.

Each frequency band has its own fader to control the gain (positive or negative).

The dbx 231s is a dual (stereo) 31-band graphic equalizer, complete with 62 faders.

Faders In Controllers

There are physical controllers for our DAWs and virtual instruments that include faders, often to control our virtual channel strips or specific attributes within our DAWs or VSTs.

The Softube Console 1 Fader is an example of a 10-channel fader control surface for our digital audio workstations.

The Arturia KeyLab 88 MkII is another example of a MIDI controller with faders (in addition to a full 88-kay keyboard).

Faders In Synthesizers

The Behringer DeepMind 12 has plenty of faders to control its sequencer, LFOs, oscillators, envelopes, and more.

Faders In Audio Effects

Audio effects are often designed with knobs to save space but can certainly be designed with faders to control their parameters.

The Electro-Harmonix POG2 comes to mind as a guitar effect pedal featuring faders.