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Analogue Plug-in Co-processor For Pro Tools
By Sam Inglis


McDSP's revolutionary APB‑16 promises to combine the sound of analogue compression with the convenience of plug-ins. Is it all too good to be true?

The most talked-about pro-audio product at this year's NAMM Show was McDSP's APB‑16. This was partly down to its eye-catching colour scheme, but mainly to the perception that designer Colin McDowell might have created something genuinely innovative — and a bit mysterious. If I overheard one earnest discussion about what could be going on beneath that Dayglo exterior, I must have heard 10. So now that it's here, does this enigmatic green machine justify the hype?

Back In The Box

There have been attempts to integrate analogue processing into computer-based mixing before, but the APB‑16 promises to take this integration to a new level. From the user's point of view, the APB‑16 is designed to behave almost exactly like Universal Audio's UAD2 Satellite units and other digital plug-in co-processors. It can be configured to perform multiple different processes simultaneously, including compression, limiting and saturation. These processes are accessed using the Pro Tools plug-in list just like conventional native plug-ins, and are controlled from a conventional plug-in GUI. They can even be automated. Inside the APB‑16 itself, however, the processing itself happens entirely in the analogue domain.

The key to all of this is the use of 'programmable analogue circuitry'. It isn't only audio signals that are fed from your DAW into the APB‑16: they are synchronised with control voltages that tell the analogue processors what to do with those audio signals. For example, when you operate the APB‑16 as a compressor or limiter, side-chain detection, equalisation and so on is handled in the plug-in, which then sends a control voltage to an analogue device within the APB‑16 telling it how much gain-reduction to apply at a given moment.

The 16 in the product name is significant, because it reflects the number of processing paths available through the unit. In other words, a single APB‑16 supports up to 16 mono or eight stereo channels of processing — and because the processing happens in the analogue domain, this number does not fall at high sample rates. If 16 channels isn't enough for you, multiple APB‑16s can be stacked in the same system. At present, however, the APB‑16 is only supported in Pro Tools systems running on Mac OS. It's perhaps a shame that although all the APB‑16 plug-ins can operate in mono, stereo and multi-mono modes, there's no true surround processing on offer; after all, where else are you going to find an analogue compressor/limiter that can handle 7.1?

All Points Bulletin

The production APB‑16 is every bit as green as the prototype on show at NAMM earlier this year, and occupies a reassuringly rugged case. It uses an external power supply, which attaches securely with an XLR cable, and the only user control is a front-panel on/off switch.

The APB‑16 needs to receive a word-clock input from your audio interface, and connects to the computer over Thunderbolt.The APB‑16 needs to receive a word-clock input from your audio interface, and connects to the computer over Thunderbolt.

The APB‑16 needs to be connected to your computer over Thunderbolt and sports two of the older mini-Displayport sockets for this purpose. It also requires a word-clock input from your audio interface. A BNC cable for this purpose is included, but you'll have to supply your own Thunderbolt cable, which is a shame.

I was expecting a bumpy ride in trying to get such a radical new device working with my not-at-all-cutting-edge system, but I couldn't have been more wrong. Driver and plug-in installation was a cinch, and once I'd connected the cables, the APB‑16 worked first time, with no fuss at all. In fact, I did not experience a single technical issue with the unit over the entire review period. For such a novel and complex product, this is impressive to the point of being pretty remarkable.

There is no control panel utility, and no settings to be made on the unit itself. In fact, from the user's point of view, the experience of mixing with the APB‑16 is exactly like that of working with digital plug-ins, with one exception: APB processing can't be rendered faster than real time, so the Pro Tools Freeze function is not available for APB plug-ins, and any mixes that use them must be bounced in real time. The APB‑16 automatically adopts the sample rate that Pro Tools is set to and, like the UAD cards, recreates the same buffer size as your audio interface; so if you are working with a 128-sample buffer, a delay of at least 256 samples is introduced each time audio is sent to and from the APB‑16.

It's easy to fill up review column inches when you're talking about something that doesn't quite work, or which is counter-intuitive and complicated. By contrast, when a manufacturer has set out to make something as simple as possible and has got it spot on first time, there's relatively little to say. So don't let the brevity of this description obscure the fact that this really is a pretty remarkable achievement on Colin McDowell's part. There has never been another analogue processor that comes close to offering this level of integration into Pro Tools, and at no point during the mixing process do you have to put in additional thought or effort to use an APB‑16 plug-in in place of a conventional one.

If the goal is to make analogue processing as easy to use as conventional plug-ins, McDSP have unquestionably succeeded.

Reaching Saturation

If the goal is to make analogue processing as easy to use as conventional plug-ins, then, McDSP have unquestionably succeeded. However, one glance at the ABP-16's price tag will tell you that it certainly isn't as affordable as using host-based processing. So if it's to justify its considerable cost, it needs to be better than native plug-ins, or at least different!

Each channel within the APB‑16 contains a number of configurable processing stages, and the initial tranche of plug-ins employs these in varying ways. What's clear is that the APB‑16's forte is amplitude-based processing: it can do compression, limiting and saturation, but not EQ or delay-based effects such as reverb, chorus and so on. There's also something a bit 'meta' about the fact that some of the APB‑16 effects were inspired by McDSP's conventional plug-ins, and that although they are truly analogue rather than digital pretending to be analogue, some of them are solid-state analogue pretending to be valve circuits.

One important aspect of the APB‑16's design concerns the relationship between the saturation stages that come at the end of the analogue signal path and the A-D converters that follow. These are aligned relative to one another in such a way that hard clipping occurs in the former before the clipping point of the converters is reached; so in theory, no matter how hard you drive the APB's analogue circuitry, it's not possible to overload the converters, meaning any distortion you hear is happening in the analogue realm.

16 Tons

C-18 Compressor.C-18 Compressor.L-18 Limiter.L-18 Limiter.At launch, six APB plug-ins are available. C-18 and L-18 are a compressor and limiter which are intended to sound 'pristine', though they can be persuaded to add some of their own sound to a track when pushed hard. El Moo and Moo Tube are also compressor and limiter variations on a common theme, this time an all-analogue emulation of vari-mu valve circuitry. Finally, C673-A and Chickenhead are more aggressive compressors designed to bring more obvious character to your tracks.

I'll confess that I have never been picky about dynamics processors, and rarely use compression 'as an effect'. Once in a while I might decide that the drum bus needs something explosive doing to it, but In general, their role for me is more utilitarian than artistic, and I get a bit nervous if the gain-reduction meter threatens to hit double figures. So when I started trying out the APB‑16 plug-ins, it was in a fairly conservative way. It was immediately obvious that these were good-sounding processors, but then there are also plenty of native plug-ins that do a perfectly good job in this sort of role. If all you ever do is shave 2dB off an acoustic guitar track here or there, the cost of the APB‑16 might be hard to justify.

El Moo.El Moo.Moo Tube.Moo Tube.However, when I decided to try doing something explosive to a drum bus, I experienced something of a lightbulb moment. Depending on which APB plug-in you use and on the time constants you select, you can easily achieve either tight, fast, aggressive limiting, colourful pumping with that characteristic 'sucking' effect on cymbals, or precision marmalising that allows kicks and snares to punch through while pushing everything else back into the mix. Having set up a couple of different effects of this sort, I thought I'd try to match them using the large selection of native compressor plug-ins in my Pro Tools system.

In a sense, it's hardly surprising that none of the native plug-ins could mimic their APB counterparts exactly, since they are all different designs — it's not as though one could compare McDSP's emulation of an 1176 against Waves' or IK's, for example. But what became increasingly obvious as the gain reduction was cranked is that all the native plug-ins sounded flat and boring in comparison with the APB processors. Even the Acustica Audio compressors, which are implemented using convolution rather than modelling, couldn't match the sense of liveliness and excitement that was coming from Chickenhead or C673-A when set to nuke the signal.

Chickenhead.Chickenhead.C673-A.C673-A.There was also a noticeable difference in the usable level that could be got out of the APB plug-ins compared with native alternatives. If you boost the make-up gain to ridiculous extremes it is possible to get the Pro Tools clip indicators to light, not because the converters are clipping but because you're asking too much of the post-conversion digital filtering. Prior to that, though, there's a huge sweet spot in which the output saturation does its work. Push it a little, and it brings a rounded, warm quality; drive it harder and the distortion is more obvious, but always sweet-sounding, and the apparent loudness that can be achieved without either triggering clip lights or robbing the sound of punch is surprising. Quite a few of the vintage emulations in my plug-in folder have saturation stages on the output that are designed to do the same thing, but none of them were as effective.

Elsewhere, the relative alignment of the APB's output stage and A‑D converter means that its limiter plug-ins make an interesting option on the master bus, keeping a firm lid on levels whilst adding a bit more colour than a typical digital limiter. And, of course, if you do want to shave 2dB off your acoustic guitars, using the APB‑16 to do it is like going to the shops in a Ferrari.

Sweet 16

When I first plugged in the APB‑16, my initial worry was that it might turn out to be a solution looking for a problem. It's undeniably an immensely clever technical achievement, but on paper, it doesn't offer as much as digital co-processing hardware. It's priced five or six times higher than UA's flagship UAD2 Satellite Octo, currently supports only six plug-ins compared to the hundreds in the UA range, and it can only ever behave as a dynamics and saturation processor, rather than implementing the full range of effects and processes offered by UAD and native plug-ins. Nor is there any equivalent to UA's Console or Waves' eMotion ST for low-latency monitoring: if you want to monitor through APB plug-ins while tracking, you'll need to reduce the system latency to a vanishingly low point, because audio will in effect be passing through both input and output buffers twice. That's plausible with an HDX rig, less so with most native systems.

However, any comparison between the APB‑16 and digital plug-in platforms hinges on them being sonically equivalent — and they aren't. APB‑16 plug-ins don't sound like digital plug-ins, and it's my belief that almost anyone who hears them side-by-side will prefer the former. Indeed, you could say that a fairer comparison would be with 16 channels of high-quality analogue outboard dynamics, in which case the APB‑16 starts to look like the bargain of the century, as well as offering all the advantages of recall and automation that come with plug-in processing.

I've never been an analogue true believer, and have always been more than happy with plug-in compressors until now, so the APB‑16's clear superiority came as a genuine surprise. If you're a serious mix engineer working in any genre where impact and punch are paramount — and that would include rock, pop, EDM and most kinds of electronica — you should definitely check it out, because it could give you a real edge over the competition.


  • A remarkable technical achievement which offers unprecedented integration of analogue processing into Pro Tools systems.
  • Extremely easy to set up, and no more difficult to use than any plug-in.
  • APB compressors sound better than digital plug-in compressors.


  • Currently available only for Mac-based Pro Tools systems.
  • Tracking through the APB‑16 would require extremely low system latency.
  • Thunderbolt cable not included.


McDSP's APB‑16 demonstrates that it's possible to seamlessly integrate analogue processing into a DAW environment — and, more importantly, demonstrates that there are good reasons to do so.


£6999 including VAT.

SX Pro +44 (0)800 6522 320.


Published November 2019