Dangerous Music’s BAX EQ is a highly refined professional interpretation using shelving filter topologies introduced by British audio engineer P. J. Baxandall in his classic paper, “Negative Feedback Tone Control,” first published in Wireless World, October 1952. The design was seminal; it was the first tone-shaping circuit where levels could be controlled by a single potentiometer without the need for a switch to select boost or cut.

The simplicity and sonic quality of the design led to its deployment as the “tone control” in countless high-fidelity preamplifiers. The design had characteristics that made it especially suitable for musical tone shaping — extremely smooth, flat shelves and minimal phase shift. The filter components reside in the feedback loop, leaving the main signal path pure. Dangerous Music’s lead designer, Chris Muth, has skillfully exploited these advantages to create an exceptional mastering-grade, analog stereo EQ.

Features

The feature set on the “BAX” is simple and straightforward; there is a low cut, low shelf, high cut and high shelf. Frequency points are linked for both channels while boost/cut levels can be set independently for left and right. This allows for M/S operation in conjunction with an external sum and difference matrix, as well as individual channel tailoring. All controls are stepped, and the corresponding internal component values are hard-switched via a network of 40 relays.


The circuitry is built from high-quality parts, selected after a year’s worth of listening with the goal of tight tolerances and musicality. All capacitors in the signal path are film-type, not ceramic. The elaborate relay-switching scheme ensures that the shelving slopes remain constant as the corner frequencies are changed. Values are dialed in with 8-position rotary switches for frequency and 21-position rotaries in .5 dB steps for level. Low-cut points range from 12 Hz to 54 Hz, low shelves from 74 Hz to 364 Hz, high shelves from 1.6 kHz to 18 kHz, and high cuts from 7.5 kHz to 70 kHz. The subsonic and ultrasonic points are intended to keep the audio band clean without side effects.

In Use

At first, the frequency values on the shelves seemed counterintuitive; they are specified with the values in the middle of the slopes rather than at the corners. The reason behind this is the gentleness of the slopes. It is this gentleness that contributes to the BAX’s extraordinary musicality. The phase shift is kept to less than five degrees for a 1 dB change, and tonal effects are heard far from the nominal values well into the midrange. It is remarkable how an EQ so simply laid out can be so versatile and effective.

The top end is capable of an effortless air, while the midrange is smoothly enhanced. The low end can create a “solid-as-a-rock” bass while warming vocals. The BAX is all about feel; it mysteriously imparts improved sonic appeal without aggressively impacting the original tonality of a mix. It can do this while neatly sidestepping two of the thorniest recording problems: thickness in the low-mids and harshness in the upper-mids. My other equalizers took on new characteristics when freed by the BAX from the heavy lifting, resulting in a range of new colors.

My first in-session use was on a well-mixed big-band project. The mix engineer had mastered the project, but the artist felt there was more potential, so the unmastered mixes were sent over. The BAX delivered — and it delivered fast. There’s something fantastic about interacting with a great analog EQ. The sweet spot came into focus quickly. It seemed too easy. My usual 5-band analog parametric EQ remained unpatched. The BAX proved itself as a true “program equalizer” in the tradition of the classic mastering EQs of simpler times. Add some nice top and bottom ... and done: The ref garnered an enthusiastic approval from the artist with no change.

Next up was an attended mastering session with singer-songwriter JD Souther who traveled from Nashville to New York for the date. JD had recorded what he felt was a personal best album and was deeply invested in every aspect of the production. JD and I had never worked together before, and both his manager and the label’s A&R executive were at the session. No pressure.

The BAX delivered a deep bass and an open, airy presence. My standard EQ was then free to handle a few notches to sweeten the vocal. After the first playback, you could hear a pin drop. Following what seemed to me a very long minute, JD said, “What’s wrong with that?” and we were on our way. On the second tune, JD asked for a .5 dB more bass. How fun was it to just reach for the BAX, twist one quick click, hit play and see appreciation in an artist’s eyes.

With the BAX, a .5 dB click amounts to a lot, thanks to the gradual slopes of the shelves. The BAX seems to do more with less, giving a track a finished polish with only a few touches. Running the shelves in conjunction with the cut filters leads to a surprisingly flexible range of curves. When used in conjunction with the low-cut filter, the low shelf can tame a tubby bass as well as flesh out a thin one. The high-cut filter serves to sweeten the top end when the upper shelf is used for a midrange lift. The device seems very transparent with negligible insertion loss.

Summary

I have been having a blast with the BAX and feel grateful to be able to benefit from the years of research and development that Chris Muth did while serving as technical director at Sterling Sound. During his time there, he ripped apart and improved just about every bit of equipment that came through the door. Chris is also a mastering engineer in his own right and, apparently, he finally built an EQ that even he could love. The BAX EQ is affordably priced well below its high level of quality. It’s like a delicious dessert with no calories.

Price: $2,529 list

Contact: Dangerous Music | dangerousmusic.com

NYC-based mastering engineer Alan Silverman is a two-time Grammy nominee in the Album of the Year category for mastering.