I never imagined that the bass and treble controls as seen on home and car stereos for decades would follow me into my professional life. That ubiquitous EQ circuit, designed by Peter Baxandall, was reimagined in 2010 for professional audio applications by Chris Muth [Tape Op #45] and the team at Dangerous Music when they released their BAX EQ [#79]. After I heard it skillfully applied to some of my work by several mastering engineers, I thought about buying a unit for myself. I hesitated long enough to discover the Dangerous Music BAX EQ plug-in from Brainworx and started there. My team and I have used it as a mono or stereo insert on clients' projects, but I always wondered whether or not the analog hardware sounded better. At NAMM 2026, Dangerous Music unveiled the BAX500 as a single channel of BAX EQ adapted for the 500 Series format. That was the inspiration I needed to finally satisfy my curiosity.
When I unboxed my BAX500, I was surprised by its substantial weight, as I knew the audio path was transformerless. I was admittedly unsurprised by its exceptional, fully American manufacturing. The hand-soldered circuitry is protected by a shielded enclosure, and the faceplate is nicely finished all the way around. Control labels and position markers are first laser-engraved, then filled in with paint to prevent fading from everyday contact with busy hands. The front panel is straightforward, but the BAX500 is neither a repackaged Baxandall tone control circuit from a vintage hi-fi nor a typical shelving EQ.
The BAX500 offers two shelving bands with highly adjustable filters and a truly linear phase response. Independent controls for each band include an eight-position rotary switch to shift the (peak) shoulder frequency, an eight-position rotary switch to select the (12 dB/octave) filter cutoff frequency, and a non-detented potentiometer to set the (+/-5 dB) gain. A non-latching button engages or bypasses the entire circuit via relays.
The frequencies listed around the Hi Shelf knob are an octave below the actual shoulder and roughly at the midpoint of the lower Q slope. On most Hi Shelf settings, the shoulder is in the (inaudibly high) ultrasonic range. The practical result of boosting that band is a continuous rise of energy starting an octave below the selected shelf frequency and extending up past the limits of human hearing. The Hi Cut filter is useful for tone shaping on that band or discreetly removing any ultrasonic artifacts from A/D converters and the induction of RF noise into the audio path. The frequencies listed around the Low Shelf knob directly correspond to the shoulder of that band, so the upper slope of the Q reaches about two octaves into the lower midrange. Once again, the very wide Q means that boosting the Low Shelf will also increase (inaudibly low) infrasonic energy. The Low Cut filter is useful for tone shaping on that band or shutting out infrasonic rumble and DC offset.