Terms that'll help you better understand EQ
In the 1950's, I'd take the family television's vacuum tubes down to Willow Grove Radio and TV Repair, check them with the giant tester machine, buy new replacement tubes, and reassemble the repaired television, so my mom and dad could enjoy their precious, respectively, Dean Martin and Red Skelton shows. In the 1960's, I studied radio and electronics at the Franklin Institute in Philadelphia. After college, in the early 70's, I joined a rock 'n roll band as the soundman, learning how to operate the electronics that make music sound good. Then, I worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems and components for recording studios, nightclubs, and touring bands. I moved back to Charlottesville permanently in 1984 and opened a little demo recording studio. I also attempted to put to practical use the creative writing degree I had picked up along the way. In 2006, I finally came to my senses and got this job at Crutchfield where they actually pay me to ramble on, rant, and explain the things I love about music, electronics, and getting good sound.
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Acoustic feedback occurs when a microphone picks up sound from a speaker and rebroadcasts the sound over and over again creating a loud ringing squeal. Audio techs use equalizers to attenuate or turn down narrow bands of frequencies in order to eliminate any feedback at those frequencies.
An analog equalizer is an electronic hardware device that uses knobs or sliders to control the level of each of the equalizer's frequency bands. On the other hand, a digital equalizer's controls are software-based.
Good articulation means that every part of a broadcast voice can be heard distinctly and with intelligibility. Equalizers are often used to improve the articulation of sound systems.
When you attenuate something you're lowering its volume. Each control of an equalizer boosts or attenuates the signal in its bandwidth.
The bandwidth, also called the Q of an equalizer's control describes how many notes are effected by that control. It's the range of frequencies that get adjusted by a control point.
You'll find two types of bass restoration processors. The first type works with factory systems, flattening out any preset low-frequency boosts or cuts so you can get the best possible performance from the subs and amps you've added. The second type can be used with any system to enhance bass response by analyzing the music and filling in low bass fundamental tones lost to compression or poor recording.
The center frequency of each band of equalization is usually labelled on a graphic equalizer, for easier identification of the sound. The full range of frequencies that band will affect is the bandwidth of that control.
Comb filtering, when certain frequencies are lost due to reflected sounds cancelling out direct sounds, is often overcome with careful equalization.
Equalizers use crossover filters for each EQ band to isolate the frequencies of interest from those that are higher and lower.
You can also use an external crossover to route the music signal to different amps in your system. Read our article about choosing a crossover for more information.
Some people think that boosting any frequency will introduce distortion, and so equalize their systems by only cutting frequencies in their adjustments. Some manufacturers offer cut-only equalizers for those customers.
A decibel (dB) is a relative measure indicating whether one signal is stronger, weaker, or the same as another. Most equalizers are marked so you can clearly see at what levels the controls are set. 0 dB means no gain or cut was applied.
An analog equalizer uses knobs and sliders to adjust frequencies, while a digital equalizer uses a menu screen that gives you much more adjustment flexibility and precision. Digital equalizers also let you store different EQ settings, very useful if you listen to a wide variety of music or take part in car audio competitions.
Digital Signal Processors
Digital signal processor (DSP) modules are a hybrid product, often combining features of EQs and active crossovers with enhancements such as adjustable listening positions and soundfields. DSP modules can be connected directly to external amplifiers. In some cases, their output can be routed back into a receiver, making an external amp unnecessary. These units often take the form of a "hide-away" module, installed behind the dash or under a seat. Some high-end EQs have built-in digital signal processors.
An equalizer is a hardware device or software app used to alter the frequency balance of an audio source. An equalizer has the ability to boost or cut specific frequency ranges based around a center frequency. Equalizers come in various forms, including parametric, graphic, active, or passive.
To learn more about equalizers, read our "how to choose an equalizer" article. Then check out our full selection of car audio equalizers.
A fader, also called a slider, is a control that is run in a straight line, up and down or left to right, as opposed to a knob that is turned.
(See Acoustic Feedback) In circuit design, electronic feedback returns a portion of the output of a process to the input, to improve performance or to better control that process.
A filter is an electronic circuit used to reject signals of certain frequencies while passing others. Equalizers use bandpass filters, characterized by three parameters: center frequency, amplitude (or magnitude), and bandwidth.
The Fletcher-Munson Curves are graphs showing the frequency response of human hearing at different loudness levels. Many audio techs equalize PA systems using these curves as a guide, so every frequency will sound the same volume. One example would be boosting everything below 300 Hz and above 6000 Hz, where our hearing sensitivity drops, and making a wide cut centered around 4000 Hz, where we hear the best.
A note is an audible tone made by air vibrating between 20 and 20,000 cycles (back-and-forth movements) per second. The exact number of cycles per second is called the sound's frequency, measured in hertz (Hz).
A system's frequency response is a measure of how well the system handles all the different frequency sounds, from lowest to highest. Equalizers are most often used to improve a system's frequency response.
A graphic equalizer is the standard type of equalizer that usually has 5 to 30 slider controls on the face whose positions mirror the frequency response curve the device is applying. These sliders let you boost or cut certain frequencies, giving you a high level of control over the tonal quality of your music. The width of each band, called the Q or bandwidth, is fixed and cannot be adjusted (unlike a Parametric EQ).
Line drivers allow you to boost the voltage of the preamp-level signal from your car stereo to the highest level accepted by your amplifiers. A higher-voltage signal travelling the length of your vehicle will pick up less noise from your car's electrical system. Many aftermarket equalizers have built-in line drivers to ensure that a robust signal gets sent to the amplifiers.
A notch filter is a cut-only equalizer, usually with narrow EQ bands, used for feedback control.
An octave is a range of notes wherein the highest note has twice the frequency of the lowest. In Western Music, each octave is divided into 12 distinct notes or tones. For a 10-band graphic equalizer, every band is one octave wide.
A hybrid of a graphic and parametric equalizer, featuring controls that graphically illustrate the EQ curve.
Parametric equalization or tone controls allow you to set not only the amount in dB by which a certain frequency band is boost or cut, but also the width and/or center frequency of this band. This gives you extremely precise control of the tonal balance in your vehicle. Parametric equalizers are more versatile than graphic equalizers, which have fixed center frequencies and bandwidths.
A passive equalizer needs no power connections, using coils, resistors, and capacitors to affect the signal's frequency response.
Pink Noise is a static-like noise techs use in conjunction with real-time analyzers (RTA) and equalizers to tune audio systems. When playing pink noise and visually observing the frequency response graphically on the RTA display, the tech can adjust the equalizer to achieve almost any response curve desired.
Q is a number that describes the bandwidth of an equalizer's control. The higher the Q value, the narrower the band.
(See Spectrum Analyzer)
A spectrum analyzer, also known as a real-time analyzer (RTA), is an electronic device which measures and displays the frequency spectrum of an audio signal in real time. It uses a number of narrow bandwidth filters connected to a display to give a visual indication of the amplitude of each frequency band. A microphone, connected to the analyzer’s input, picks up the all-frequency pink noise you play through the system, and the RTA displays its response onscreen. Spectrum analyzers are commonly used to help equalize a speaker system to the installation space.
For more details about how we use real-time analyzers, read our article about car audio testing tools.
Subwoofer Level Control
Some equalizers have a built-in volume control for your subwoofer. It boosts or attenuates the signal going to your subwoofer, letting you raise or lower the bass as needed.