What is Baxandall EQ? How to use it in mixing and mastering

Unless you’ve been living under a rock for the better part of the last decade, there’s a good chance you’ve heard chatter about Bax – or Baxandall – EQs in audio engineering circles. Although its roots go all the way back to 1950, it was the release of the modern Dangerous Music BAX EQ around 2010 that catapulted it back into the audio engineering zeitgeist.

But what exactly is a Baxandall EQ, and what makes it so special? Moreover, how should you put it to good use in your productions, mixes, and masters? In this article we’ll dive into all that and more. 

Follow along with this tutorial using  Nectar ,  Neutron , or  Ozone , or try all three as part of  Music Production Suite .

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What is Baxandall EQ?

A Baxandall EQ is a special type of shelving equalizer based on a circuit developed by English electrical and audio engineer Peter J. Baxandall in 1950. In fact, it’s often called a tone control, and if you’re old enough to remember the “bass” and “treble” tone knobs on older hi-fi stereo systems, there’s a good chance they were Bax filters under the hood.

So what makes these filters so special? If they were in countless consumer home and car stereo systems, why would we want to use them in mixing or mastering? In a nutshell, it’s the shape and slope of the high- and low-shelf filters in a Bax EQ that sets them apart.

Baxandall shelves have a very wide and gentle Q-factor which gives them two rather unique properties: first, the phase shift is greatly minimized and spread over a wider area than with conventional parametric shelves, and second, in their useable frequency ranges most of the affected audio frequencies fall under the rising – or falling – parts of the Baxandall EQ curve. By the time a Bax shelf flattens out it’s so high or low that it’s beyond the limits of the human hearing range.

Taken together, these properties have the effect of giving Bax shelves a very transparent and musical sound. While that does make them particularly well suited for consumer applications where simple controls are needed, they can also be extremely useful in mixing and mastering for general tone shaping duties.

Analog vs. digital Baxandall EQ 

Of course, being from the 1950s, Baxandall’s original design was analog, as was the Dangerous Music reboot over half a century later, but Baxandall EQs don’t have to be analog. In fact, since transparency is often one of the primary goals of Bax EQs, it’s a great candidate for digital where distortion and noise can be all but eliminated.

How does Baxandall EQ work?

The circuit for a Baxandall EQ is surprisingly simple, consisting of nothing more than a few capacitors and resistors, and an amplification stage with negative feedback. Originally, the amplification was achieved with tubes, but in modern circuits integrated – or discrete – operational amplifiers are commonly used. In essence, a Baxandall tone control is a collection of very simple passive high- and lowpass filters, cleverly configured in a negative feedback arrangement. For more detail on the internal workings, check out this article about amplifier tone control. 

Not only that, but digital offers some flexibility that’s much more difficult to achieve in analog. Without getting too far into the weeds, the frequency selection in an analog Baxandall EQ is determined by the values of several capacitors, and since audio runs through them they have to be very high-quality, and precisely selected and matched for stereo operation – and that’s just for one frequency. Of course in digital you can get perfect stereo matching, and at any frequency you like.

However, if you’re looking for some of the streamlined workflow inherent to one of the finest analog Bax EQs in existence, you’re in luck! Plugin Alliance has an exacting replica of the Dangerous Music BAX EQ from Plugin Alliance that gives you the best of both worlds – plus some digital-only extras like mid/side mode and the ability to unlink the left and right channels.

How to use Baxandall EQ in mixing and mastering 

So, now that we know a bit about what makes Baxandall EQs special and unique, and how they behave, what I’m about to say should come as no surprise: if you need surgical EQ moves, a Baxandall filter won’t get you there. However, if you’re looking to add some presence, sheen, gloss, air, etc. to the high end without things getting harsh, or you need to add some heft or weight to the bottom without things getting boomy or muddy, Baxandall shelves are a great choice.

With that in mind, let’s take a look and listen to how to put them into use in mixing and mastering with no less than five options available to you in the Native Instruments family of brands.

Using Baxandall EQ for vocals

If you’re trying to get that airy shimmer and sparkle on a vocal that we so often crave, the Baxandall high shelf in Nectar is a great place to start. Conversely, a cut with a Baxandall high shelf can be a great way to soften an overly bright vocal, or push backing vocals a little further back. Let's listen to both.

First, here’s a lead vocal both flat and with some added shimmer from a Bax high shelf boost.

Next, here are some background vocals that can be made to sound a bit further away by using a Bax high shelf cut.

To access the Baxandall shelves in Nectar – or any other iZotope plugin – simply create an EQ node, click on the filter shape dropdown in the band controls panel, and select “High Shelf > Baxandall” – or “Low Shelf > Baxandall” – as shown above.

Advanced vocal tip

Baxandall low shelves can also be used on vocals, but they warrant a little caution. You’ll likely need to set them to a higher frequency – perhaps around 550 Hz – than is normally employed for a Bax style low shelf. This can add some really lovely warmth to an anemic vocal, but because the Bax shelf continues rising down to 20 Hz and below, it can add a lot of infrasonic rumble. To combat this, add a flat high-pass filter with a cutoff a bit below the lowest vocal fundamental.

Using Baxandall EQ on instruments

Baxandall shelves can also shine on many instruments and buses. For example, here are some high and low boosts on a string group using the Bax filters in  Neutron .

Not exactly subtle, eh? Of course, any moves like these need to be considered in the context of the full mix. If the rest of the mix dictates a more midrange-forward sound for the strings – or any other element – this wouldn’t really be suitable, and perhaps Baxandall cuts at these exact same frequencies would be more appropriate.

There are no rules here, so feel free to experiment. Low Bax boosts can be a lot of fun on kick drums or basses if you’re after a ton of weight – although it’s probably best to pick one or the other in any given mix – and high boosts can add gloss and shimmer to drum overheads, acoustic guitars, synths, and more. Just be careful not to get carried away, as the sound of Baxandall boosts can be rather addictive! 

Using Baxandall EQ in mastering

Given that Peter Baxandall originally designed his EQ circuit as a tone control for program material, it should come as no surprise that it shines as a mastering tool. You can access the Baxandall shelves in  Ozone  in the exact same manner as in Nectar and Neutron, but there are a few subtle differences in Ozone.

The first is just a small visual change. Since EQ moves in mastering tend to be subtler than in mixing, the vertical gain scale in the EQ graph reflects that. Second, although the phase shift of Baxandall filters is already extremely small, you can put Ozone into digital mode to achieve a linear phase response if desired.

When using Bax shelves in mastering it can certainly be easy to overdo it. To help mitigate this tendency, I like to start with a boost of 1–2 dB and with the frequency set all the way up at 20 kHz for a high shelf, and down near 50 Hz for a low shelf. Then, slowly work the frequencies toward the center. This makes it easier to find the point where the boosts are doing just enough without going overboard. From there you can fine tune the gains as needed.

Lastly, I’ve been talking a lot about boosts – let’s be honest, that’s what’s most fun about Bax filters – but you shouldn’t discount them for gentle, transparent cuts either. Whether you’re working on a song that’s just got a little too much edge up top, or is too thunderous down in the low end, a Bax shelf can be a great way to tame those regions without them sounding obviously EQ’ed.

Additional options from Plugin Alliance

There are also two offerings from Plugin Alliance that offer Baxandall filters for anyone who’s interested in units that accurately emulate their real-world analog counterparts. The Louder Than Liftoff SILVER BULLET mk2 is an all-around mojo and tone box, with several flexible saturation stages, followed by Baxandall filters with some carefully chosen fixed frequencies.

For the purists, there’s also the aforementioned Dangerous Music BAX EQ which comes with both “mix” and “master” versions of the plugin. The mix version gives you a single set of controls, while the master version allows stereo unlinking and mid/side operation.

You may also notice that the Dangerous Bax includes highpass and lowpass filters. These can be very useful, especially on masters since the nature of Baxandall shelves is to boost frequencies far beyond their set point. This means that a low boost can bring up a lot of infrasonic rumble, while a high boost can bring up a lot of ultrasonic noise. 

While these frequencies may be inaudible to human ears, they can eat up headroom, and exacerbate aliasing and intermodulation distortion issues. By bookending the Bax curves with high- and lowpass filters, you can get the audible benefits without the out-of-band drawbacks.

Start using Baxandall EQ in your production process 

Fundamentally, Baxandall EQs are fairly simple both in design and usage. As always though, knowing a little more about how they work and what makes them unique is hardly a bad thing. You now know the details of what sets the Baxandall curves apart from other shelving EQs, how digital and analog versions can differ, and how to approach their use in mixing and mastering.

If you’re looking for tips on how to EQ different mix elements with a parametric EQ, this EQ cheat sheet article is a great place to start, and if you’re wondering how to integrate EQ and compression we’ve got you covered there as well. So until next time, good luck and happy Bax-ing!

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