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Bass Enhancement Plug-in For APB By Sam Inglis
Published April 2024


McDSP’s latest hybrid plug‑in refreshes the parts of the frequency spectrum other tools can’t reach.

As well as being the greenest item in any given studio, McDSP’s Analog Processing Box is one of the most versatile. It hosts an array of configurable analogue devices that can implement many different styles of dynamics processing, ranging from emulated variable‑mu valve compression to hard limiting, as well as subtle or less subtle saturation. These are bookended by D‑A and A‑D conversion and accessed through a Thunderbolt connection from your computer, from user interfaces that behave exactly like conventional plug‑ins. APB processors ‘live’ in DAW insert slots and can be stored, recalled, loaded, saved and automated in exactly the same way as any other real‑time plug‑in, the only caveat being that, for obvious reasons, faster‑than‑real‑time bouncing is not possible.

Say Hello To BOB

Since its launch back in 2019, the library of APB plug‑ins has grown. The original line‑up of compressors and limiters has been joined by a valve‑style mixer, a hybrid EQ with analogue saturation, and a multiband compressor. The latest addition to the list is another hybrid plug‑in. BOB APB is based on the Bass Optimized Bias module developed for McDSP’s 6060 plug‑in, which is conceptually a sort of virtual 500‑series rack. The tone‑shaping aspects of the APB version are still handled digitally, but it adds what McDSP’s Colin McDowell describes as “headroom stuff” and saturation in the analogue domain.

Functionally speaking, BOB APB can be thought of as a low‑frequency enhancer. Unlike, say, the dbx Subharmonic Synth, or a guitar octave pedal, it doesn’t synthesize harmonic content below what’s present in the original material. Rather, it seems to apply something more like a resonant EQ, before using compression and saturation to thicken up the resulting sound.

The core controls of both BOB APB and its native antecedent are fairly simple. Two ‘styles’ of bias are available, labelled simply A and B. The Freq control sets the frequency at which the process is focused, and the Bias control determines how hard it’s pushed. With Bias at 0% and style A selected, the Freq control acts like a high‑pass filter; as you turn up the Bias, you begin to hear a resonant ‘thump’ at your chosen frequency, while frequencies below this start to make it through again, albeit at a lower level. Style B is more subtle, and perhaps more like a resonant shelving band. The Squash control applies frequency‑sensitive compression, with a Rate control governing release time.

I often find that synth basses are too subby... and BOB APB makes it easy to rebalance the tone so that it will be audible on small speakers without robbing the synth of its impact.

Unique to the APB version of the plug‑in are two saturation modes, labelled I and II. These can be used independently or together, and a single Gain control sets how hard the saturation should be driven. An output Trim control lets you rein in the signal at the back end.

To get you started, McDSP have helpfully supplied a decent selection of presets categorised by application: Bass, Drums, Guitars, Mix and More. These certainly aid the orientation process, but operation is generally quite intuitive, and it won’t be long before you can do without.

Light Touch

I was pleasantly surprised to find that there are subtle and non‑obvious applications for BOB APB. For example, during the review period I was working on a restoration project with audio that had been recorded off the radio before passing through several generations of cassette dubbing. Some of the tracks were simultaneously woolly and overbearing in the low midrange, whilst lacking in true bass. Although BOB doesn’t synthesize subharmonic content, it was able to work effectively with what little there was in the sub‑100Hz region to regenerate a feeling of proper low end.

Most of the time, though, you’ll want to be using this plug‑in in rock, pop and electronica mixes, and here it can be devastating. I often find that synth basses are too subby, for example, and BOB APB makes it easy to rebalance the tone so that it will be audible on small speakers without robbing the synth of its impact. The saturation tends to be quite subtle unless driven hard, but can really help things cut through in the midrange.

Likewise, if you’re afflicted with an anaemic bass guitar recording, or even a thin‑sounding vocal track, BOB offers a surprisingly broad range of treatments. By far my favourite application for it, though, was on bass drums. There’s something magical that happens when you crank up the Bias at 60 or 70 Hz before applying gobs of compression to rein it all in again. Topped off with a helping of analogue saturation, it just seems to turn almost any kick drum track into something punchy and solid that waves the rest of the mix aside contemptuously whilst simultaneously belonging perfectly in the track. It’s a trick that I’ve sometimes been able to pull off using the Thump button on Soundtoys’ Decapitator, but APB BOB makes it a lot easier to achieve.

If you’re afflicted with an anaemic bass guitar recording, or even a thin‑sounding vocal track, BOB offers a surprisingly broad range of treatments.

Bass enhancement is quite a specialised process, and although I can well imagine wanting to use BOB on every kick drum track from now on, the reality is that not every mix really needs it. And in a sense, that’s the beauty of the APB system. You might cavil at the idea of spending a lot of money on a hardware box that only did what BOB APB does — but as far as McDSP’s Analog Processing Box goes, it’s simply one more arrow in the quiver. Or should that be a feather in the cap? Either way, this is yet another well conceived and well implemented processor that proves the fundamental strength of the concept.

Low Latency Mode

Like a conventional computer audio interface, the Analog Processing Box [APB] needs to buffer the audio that it sends out to and receives back from its D‑A and A‑D converters. This buffering introduces a latency or delay, which is reported to the host DAW and compensated for, so not a problem at the mix. But if you want to monitor or track a live input through an APB plug‑in, the total latency would be equal to that of your audio interface and the APB added together (plus some additional fixed latency on both fronts), and this can be an issue.

When I first reviewed the APB16, I mistakenly reported that its buffer size always mirrored that of the host DAW. In fact, it was fixed at 1024 samples, and hence was really too slow to ever be used on a live input that was part of a performer’s cue mix. In beta at the time of writing is a new Low Latency Mode, which makes the APB operate as I thought it always did! With this installed, APB latency changes with the audio interface buffer size you choose in your DAW. At the lowest 32‑sample setting available in Pro Tools, an APB plug‑in now reports a delay of 207 samples, which equates to 4.7ms at 44.1kHz. On my rather modest Intel Mac Mini, this gave rise to clicks and pops, but moving to a 64‑sample buffer only raised the APB delay to 231 samples, and that worked fine. Note that if you want to use more than one APB plug‑in in series, the delay will be cumulative, as each one you add introduces a new round trip.


A versatile and easy‑to‑use bass enhancement tool that might just be the magic bullet for weedy kick drums.


Free for APB owners.

Free for APB owners.