EQ - Audio Hertz

Posted on September 9, 2020December 27, 2022 by David Silverstein — Leave a comment

What the f*ck is a Baxandall EQ?

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You’ve probably seen plugins, guitar amps, or stereos that replicate a Baxandall circuit, or maybe you’ve heard of the popular Dangerous BAX mastering equalizer. Peter Baxandall designed the Baxandall tone circuit or EQ in 1950, and they were then implemented into millions of audio systems around the world.

So what is a Baxandall equalizer circuit, and what makes it different than other equalizers?

The Baxandall equalizer is a shelving EQ, but unlike traditional shelving EQs, which have a steep rise or fall above the set frequency, the Baxandall shelving curve has an extremely wide Q curve, which creates a gentle slope. The broad curve can adjust a large portion of the frequency spectrum, but the gentle slope allows for a more natural sound and minimal phase distortion. The minimal phase distortion enables users to make more drastic boosts and cuts without imparting negative artifacts into the signal. This results in a wide, open sound that enhances the source’s sonic character that’s already there rather than imparting its own sonic character. These equalizers offer a subtle yet remarkably effective way of adjusting the frequency spectrum, which is why you’ll often find them being used on the mix bus and for mastering.

History

During World War II, Baxandall consulted for the Telecommunications Research Establishment in the Circuit Research Division. It was there he spent his time working on many different types of projects, including frequency transformers, powered loudspeakers, oscillators, high-speed tape duplicating equipment, and high precision microphone calibration methods, among many more things. His hero, Alan Blumlein, who you might know for his stereo micing technique, also worked for the TRE.

Lucky for us, Baxandall was enormously generous and patient with passing on his knowledge. He was also remarkably good at conveying very complicated topics in a simple and easily understandable form. He published his tone circuit in a 1952 article in Wireless World magazine. Have you ever seen the Bass and Treble knobs on a stereo? That’s likely a Baxandall EQ circuit. He never collected a single royalty, while even a minuscule percentage would’ve made him an extremely wealthy man. This might be the greatest testament to his generosity; he genuinely wanted the world to sound better.

More History

The term equalization was likely derived from the various operators’ requirements at the time (phone, motion picture, broadcast, etc.) that were attempting to get their audio back to a flat frequency response or equal. Equalization, or filtering as it was also called, has been part of audio equipment since the beginning of the technology. Early radios came equipped with high frequency or top cut filters to remove unwanted noise or artifacts. Early telephone lines used equalizers to put back the high end that was lost in transmission. These equalizers were not fully adjustable like the parametric equalizers you’ll find in your DAW today.

Do you want to try a Baxandall EQ?

These plugins are available for free,
Acustica Audio Coral Bax-ter EQ
Kuassa BasiQ
Fuse Audio Labs RS-W2395C Baxandall EQ

What the f*ck is Linear Phase EQ?

Fab Filter’s Pro-Q 2 and Wave’s Linear Phase EQ are two of the most popular Linear Phase Equalizers.

A minimum phase EQ is just another name for your standard, everyday equalizer. Your Neve 1073, API 550, your Pultec EQP-1A. All of these equalizers experience phase shifts due to the latency created by changing the amplitude of specific frequency bands. This latency or delay of the frequencies causes what’s known as a phase smear. Smearing leaves audible artifacts in the signal, which can be undesirable. Many times you can’t hear smearing at all, other times, you may like what it’s doing, but in different scenarios, you may want an equalizer that keeps the phase consistent (more on those later).

In the analog world, phase smear was just something that product designers tried to minimize or mold into something that sounded pleasing. In the digital world, all bets are off. When plugin coding and processing power started to become more advanced, developers realized they could finally do what engineers have wanted to do this whole time. Linear phase equalizers are impossible in the analog world, but in plugin land, anything is possible. Linear Phase EQ is equalization that does not alter the phase relationship of the source— the phase is entirely linear.

The irony of Linear Phase EQs is that they were initially conceived because of an engineer’s desire to eliminate phase smearing, which was thought to be a negative byproduct of using analog hardware equalizers. Once software programmers were able to develop a Linear Phase EQ, they soon realized that there were new problems and artifacts to overcome.

Pre-ringing is a negative artifact commonly associated with using Linear Phase EQs, which affects the initial transient. Instead of starting with a sharp transient, there is a short but often audible crescendo in the waveform before the transient hits. Since it happens before the transient, it sounds very unmusical and displeasing. This affects the overall tonality of transients which people do not find desirable.

The next obvious question… When are you supposed to use one? What are they good for?

Well, that answer depends on the engineer you ask. There are a lot of engineers that might tell you there is never a good reason to use a Linear Phase EQ. There were thousands and thousands of records made before plugins and Linear Phase EQs existed, and a lot of them sound pretty damn good. I can’t fault an engineer who doesn’t even bother with ever using one.

Other than never, there are a few scenarios where you might want to try a Linear Phase EQ. One of those is when boosting or cutting on sources that were multi mic’d. Since the phase relationships between each mic are so important, a Linear Phase EQ will ensure the phase coherence stays intact even with processing.

Another time you may want to pull out the ol’ Linear Phase EQ is when equalizing parallel tracks. When you have two of the same tracks, and you insert an equalizer, the phase of when the signal will change when combined with the unprocessed channel. This may, in fact, make it sound better, and you may like it, or it may make it sound worse; in this case, you could try reaching for a Linear Phase EQ to retain the phase relationship while still being able to boost and cut frequencies on the parallel channel.

Tag: EQ

What the f*ck is a Baxandall EQ?