How Does an Audio Tone Control Work?

Tone controls use common analog electronic components to filter audio signals.

An audio tone control is a filter in the audio-signal path that allows the end user to control which frequencies--usually bass, mid and treble--to enhance or decrease. Tone controls work by using capacitors, resistors, inductors and amplifiers to filter certain bands of frequencies.

Potentiometer

The potentiometer, commonly called a pot, is the most common physical form of a tone control. Simply put, it is a volume knob that increases gain when turned clockwise and decreases gain when turned counterclockwise.

Cut and boost

Instead of affecting the overall volume of an audio signal, the tone control changes only a specified frequency band. The decreasing and increasing of a tone are referred to as cut and boost, respectively.

Electronics

While there are many ways to design the specific circuitry of a tone control, most use a potentiometer and all use a series of resistors and capacitors of varying values. Capacitors are particularly useful in audio filtering because their impedance--how much they impede the signal--is inherently related to the audio frequency.

Single-knob Tone Control

Some audio circuits offer only one control for tone. This is common on electric guitars, where often there is one pot for volume and one for tone. This tone control is actually only a high frequency cut.

References

• All About Circuits: Design Project--Audio Tone Control
• Elliot Sound Products: Beginners' Guide to Potentiometers
• Guitar Nuts: How Volume and Tone Controls Work