About Equalizers
Summary
Equalization is a form of Digital Signal Processing
…but the most interesting DSP when talking about headphones is equalizing so headphones/earphones sound more natural, or more fun
Equalization is the largest upgrade to sound you can make
…short of buying much more expensive headphones/earphones
Equalization apps are cheap
Often £0–£20 for a digital app
Equalization apps are fiddly, and for many people too much trouble
On computers they involve tricky configuration. Due to security reasons, mobile phones prevent many possibilities, meaning equalizers may not work all the time, and/or you may need to switch players to make them work
Adjusting equalization is not easy
Most apps have presets, but these are usually rough. Good coverage of this subject is a university course
About
Equalization means adjusting the volume of different frequencies replayed by a device and headphones/earphones. So you can make more ‘treble’ or ‘bass’. You may want to do this because you like more ‘treble’ or ‘bass’. Or you may want to do this because what you own sounds wrong, and you want to correct it.
The equalizers we talk about have many more volume controls than ‘treble’ or ‘bass’. They may have three to thirty controls, so can for example boost lowband, push the midband forward, or fix a screechy highband.
Can an equalizer make my £8 earphones sound like £800?
No. Changing the frequency response can not make cheap gear sound like expensive gear. But it can overcome limitations or incompatibilities.
I didn’t think anyone used equalizers besides recording studios?
For a long time equalizers were avoided in replay. Most sound replay gear was analogue. If you add gear to change analogue signals, the gear will degrade the signal (this is a bland argument—if you like, you can read more). Nowadays people are using smartphones and portable computers, where the signal is digital. The losses are far less.
About equalizer apps
How much do they cost?
For the kinds of general applications we talk about, £0–£20
Are equalizer apps too much trouble?
Only you can decide. If you’re not happy installing apps and meddling with settings, avoid. Effects apps, including equalizers, are particularly difficult on smartphones, where they may not work with sound from the web or some players. But marked improvements to replay can be made. See AutoEQ.
Does it matter how many bands/‘slots’ an equalizer has?
Yes. An equalizer with two bands is a ‘treble/bass’ control, and these have always been regarded as useless—they operate over too many frequencies. Ten bands is usually regarded as good for adjustment of an output.
(you didn’t ask but…) How do I adjust the volumes?
Not as easy as it seems. Let’s say you have a more sophisticated equalizer than a treble–bass. You try adjust and don’t get lost pushing knobs up and down. Then you find that you adjusted for one track, but the settings will not work on another track. There are solutions—we discuss what the apps do in the reviews.
What is a ‘parametric’ equalizer?
Most equalizers split the audio spectrum into slots, then you adjust each slot. Parametric equalizers let you pick the spot where a particular volume will act, but also the width of frequency the boost/dip will act over. This is much more subtle, but difficult to set up and use.
The position of equalizer apps
Sound in computers is organised in chains. Sound starts at a source, runs from the players through effects then amplifiers to the replay gear. There are usually many chains, from many sources, so these get mixed together for the output. Effects like equalizers can be placed at many points in the chains.
There seems to be equalizers added to everything!
True. You can find add‐ons that plug into browsers, sit in playback devices, tap into audio chains, or filter the final mix. None of them are perfect.
But I only want to tweak my headphones (or loudspeakers)!
One place will work for most people, most of the time, which is to place the effects in the final mixer. Computers can do this, but smartphones, for security reasons, block anything that interferes with overall settings.
Why isn’t the final mixer a good position?
It’s a good position, but not perfect. The ideal equalizer app, for our purposes, would let you define the effect for,
the source, “Use my settings for sounds from the music library and system sounds but not the web”
the replay device “Use these settings whenever I plug in my best headphones (but not anything else)”
the type of sound (music/news/podcast/video/chat etc.)
This is impossible. Sound systems nowadays send a message when apps are starting, so some ‘system‐wide’ apps can react and put a different effect on playback from files but not from the web (or visa‐versa). But they can’t mark the difference between the sound of the news and music. Same for playback, computer sound systems can tell the difference between playback on speakers, socket outputs and microphone inputs, but they can’t tell what is plugged in. On smartphones, ‘system‐wide’ apps may not know if a sound is playing at all.
Why don’t headphones have EQ inside them?
That would fix many issues. So a handful of expensive models do. But the reasons why not are obvious—it costs money, it can only be done with big headphones, and it means an extra app to adjust the settings.
AutoEQ
What is AutoEQ?
It’s an index of settings for equalisation that ‘correct’ the far‐from‐perfect replay of headphones and earphones
That can be done?
HiFi people love measuring the frequency profiles of their far‐from‐perfect sound replay gear. Result is, the data for thousands of headphones/earphones is freely published on the web. This data can tell you where the headphone is ‘good’ or ‘bad’. With that information, the correction a headphone needs can be worked out, such as ‘this one needs less bass and more voice’.
Why don’t the manufacturers build headphones/earphones right to start with?
Headphones and earphones (and loudspeakers) are a simple idea and imperfect. That’s why there are thousands of different types on sale. And then, there’s more to sound replay then equalization.
Why don’t they build the corrections in?
Nobody is agreed how to do this—and people who produce music need different equalization. It’s only in the last fifteen years anyone has reached some agreement about standards for replay, and these standards are a long way from fully researched. Also, physically, how would equalization be built in? An equalization chip can be squeezed into a headphone, but not an earphone—and will you pay for it?
What’s this AutoEQ thing?
The various databases have been gathered into one large index. The index is called AutoEQ. Go there and see if your headphones/earphones are listed. If they are, you can download then apply a corrective equalizer setting.
Is an AutoEQ correction any good?
At first headphone corrections were an ad‐hoc interest. Nowadays some Hi‐Fi enthusiasts think no modern digital system should be playing without headphone‐correction. Stick my neck out, it’s like spending half or same price again on your replay gear. But …downside. AutoEQ correction means running an equalizer app, which for many people is too much trouble.
Sounds interesting?
Precisely. AutoEQ generates various formats from the many available headphone/earphone frequency sweeps. Nobody is saying this is perfect. To get technical, the corrective equalisations generated are set to standard curves, which is not for everyone. Harmon, who publish the most well‐known curve, themselves have published curve revisions for younger people which favour ‘bass’, and for older people which favour ‘treble’. Hi‐Fi people will want to tweak the curves for further purpose. But when all that is said, and debates wane… for the average listener an AutoEQ corrective equalisation will provide a startling change. And maybe a permanent upgrade.