You are here

JoeCo Cello

USB2.1 Audio Interface By Sam Inglis
Published April 2019

JoeCo Cello

JoeCo's debut desktop interface combines high sound quality, robust engineering and some unusual features.

Former SADiE developer Joe Bull has a knack of spotting gaps in the market, and launched JoeCo to develop multitrack recorders for capturing live shows. Rugged, super-reliable and compact, JoeCo's BlackBox Recorders come with a range of I/O options that allow them to hook into mixer insert points, digital outputs or mic splitters, and have become the de facto industry standard in some quarters.

The BlackBox Recorders are stand-alone devices, so it was a logical development to launch the BlueBox Recorder. This too can record and play back 24 tracks of audio to and from local media, but adds, among other things, the ability to serve as a USB audio interface for Mac OS and Windows. I reviewed the BBRW24MP in SOS May 2017; considered as an interface for studio use, it makes an intriguing alternative to the familiar choices.

Emboldened by that success, Joe and his team have now created the Cello, a desktop USB interface designed for home and studio use. On paper, its feature set looks much more conventional than that of the BlueBox, boasting two mic preamps, a high-impedance input for guitars, a pair of headphone outputs and monitor control functionality amongst other things; but, as we'll see, there are still respects in which the Cello differs from its peers.

Cello Case

One aspect of the Cello that immediately marks it out as different is its industrial design. It occupies a chunky brushed-metal housing and offers hands-on control courtesy of chunky retro knobs and attractive 'Opal fruit' buttons with integral LEDs. Further visual feedback comes from six-segment LED ladder meters embedded into the top panel, and a two-line text display that looks as though it belongs on a sampler from 1989. Taken as a whole, I think it works well, making a bold visual statement whilst feeling very robust and substantial. My only slight reservation is that the buttons don't feel as good as they look.

The tiny on/off switch on the Cello's rear panel is an unusual momentary affair rather than a conventional toggle, but the unit itself leaves you in no doubt as to whether it's powered up. In theory, the Cello can run on bus power, but an additional 5V power supply is included in case your computer can't supply enough juice. My MacBook Air failed dismally on this front, and I was only able to use the Cello with the external PSU. This is inconvenient, as it's a wall-wart affair that comes with a cable only 1m long.

In this day and age, JoeCo's decision to include five-pin MIDI in and out sockets is unusual (and welcome) in itself. These are on the left-hand side panel, while the audio I/O is divided between the front and rear. The front sports two Neutrik Combo mic/line sockets, plus the quarter-inch instrument input and two quarter-inch headphone jacks. On the rear panel, meanwhile, we find the main stereo monitor outputs, again on quarter-inch jacks, plus the line-level and digital I/O. The latter comprises two optical inputs, catering for up to 16 channels of ADAT-format audio, and a pair of coaxial sockets that can be switched between S/PDIF and word‑clock in and out.

The Cello's back panel houses connections for USB, an external PSU, monitor outputs, S/PDIF, word‑clock and ADAT I/O, line inputs/insert returns and insert sends. The unit's full-size MIDI ports are found on the left-hand side.The Cello's back panel houses connections for USB, an external PSU, monitor outputs, S/PDIF, word‑clock and ADAT I/O, line inputs/insert returns and insert sends. The unit's full-size MIDI ports are found on the left-hand side.

The Best Of Both Worlds

Most interesting, and unusual, are the line-level analogue I/O arrangements. There's a pair of balanced quarter-inch inputs, plus a further pair of balanced jacks that act as insert sends from the two front-panel mic channels. Using the inserts deprives you of the separate line inputs, because these become insert returns, but the big plus is that the unprocessed mic signal is still available as a recording source in your DAW. It's thus possible to connect an outboard compressor or EQ as an insert, then to monitor and record this signal through the line inputs, while also recording an uncompressed 'safety' copy of the mic input to a separate track. I like this setup a lot, and I can't immediately think of any other interface that works this way. (It would be even better if the mic signal and insert return were perfectly phase-aligned; as it is, the latter seems to be delayed by a single sample, at base sample rates.)

The sharp-eyed will notice that there are two types of position indicator on the top-panel knobs. The mic preamp and instrument gain controls are conventional analogue potentiometers with a fixed travel, while the headphone level controls, like the main monitor volume, are endless rotary encoders (which begs the question of why they have position indicators at all). Input gain control is actually split between the analogue and digital domains. All the mic-input buttons, including the pad, are reproduced in the JoeCoControl utility; and the line inputs also have a preamplifier which has only digital gain control. Curiously, the variable gain runs from +20 to +40 dB in half-decibel steps, and if you want the line inputs to operate at unity gain, you have to use the lowest setting and engage the -20dB pad.

The Cello's front panel features two Neutrik Combo XLR/jack sockets, a quarter-inch instrument input and two quarter-inch headphone ports.The Cello's front panel features two Neutrik Combo XLR/jack sockets, a quarter-inch instrument input and two quarter-inch headphone ports.

Levels for the two line inputs can be set separately in software, but there's also a top-panel encoder that adjusts both simultaneously, preserving any offset between them. The same encoder is also pressed and held to activate the built-in talkback (latching mode is available only in software), an arrangement which runs the risk of the engineer accidentally changing the line input gain whilst attempting to communicate with the musicians. The built-in talkback mic is located right next to the encoder, and consequently transmits an unpleasantly loud 'thunk' when this is released. On the plus side, it's available as a source for recording, allowing you to slate takes and so forth.

The two headphone level controls also have a press function, in this case relating to the mic preamps. By default, these have a flat frequency response, but JoeCo's Top+ option lets you add extra sparkle courtesy of a fixed shelving EQ boost turning over at 10, 12, 14, 16 or 18 kHz. Though it's controlled digitally, this operates in the analogue domain, as does the high-pass filter; this is as it should be, since one of the main reasons for putting a high-pass filter in the input chain is to protect the A-D converter from being overloaded by subsonic thumps and rumbles.

My tests did uncover some issues with polarity not being preserved across all the inputs and outputs, but JoeCo said they expect to be able to resolve this in a firmware update which should already have happened by the time you read this. Minor quibbles about the talkback aside — and it's great to have talkback, which is a glaring omission from many interfaces — the whole system is pretty comprehensive and well thought-out, though I can't quite fathom why JoeCo haven't put all of the input gain settings under digital control rather than just some of them.

JoeCo make available comprehensive specifications for the Cello, and these demonstrate a uniformly high level of performance. The mic inputs can apply up to 78dB gain, with EIN quoted as -127dBu unweighted, while dynamic range on the line inputs and outputs is 120dB and 127dB respectively. Most of the analogue circuitry also boasts a frequency response that is said to be flat up to the Nyquist limit — which, since the Cello is one of very few audio interfaces that can record at 354.8 and 384 kHz sample rates, could be as high as 192kHz! Interestingly, lurking in the control panel software are options for 'ADC Setup' and 'DAC Setup'. These change the shape of the anti-aliasing and reconstruction filters, with a choice of options that range from 'Maximally Flat' to 'Musical' and 'Ultra Musical' at the other. Who doesn't want their conversion to be ultra-musical?

Cello Control

An attached computer 'sees' 24 inputs and eight outputs from the Cello. None of the inputs showed up with descriptive names in Pro Tools on my system, but it's easy enough to figure out that 1/2 are the mic inputs, 3 is the instrument jack, 4 is the talkback mic, 5/6 are the line-inputs-cum-insert-returns, 7/8 are the S/PDIF ins and the rest are all ADAT ins. By contrast, physical outputs are not addressed directly: instead, the eight outputs available in software show up in the Cello's internal DSP mixer as four pairs of stereo 'stems'. These, along with direct signals from the inputs, can be mixed in any combination to the main outs, the two headphone outputs and the S/PDIF outputs.

The JoeCoControl utility now allows individual panels to be separated from the parent window and independently resized.The JoeCoControl utility now allows individual panels to be separated from the parent window and independently resized.

This is achieved using the same JoeCoControl utility that is supplied with the BlueBox Recorder, slightly tweaked to reflect the different purpose and I/O configuration of the Cello. The main difference is that the Live and Mix modes have disappeared, which is sensible enough, since they are not really relevant to typical Cello applications. (You also lose some of the inputs and outputs at 354.8 and 384 kHz, which I think is unlikely to bother anyone much.)

JoeCoControl is likely to see much more intensive use with the Cello than would typically be the case with the BlueBox Recorder, so it was with some relief that I installed the v1.2.0.0 update that became available around Christmas 2018, because this brought with it two features that make a huge difference to its usability. The first is the ability to hide the digital input channels when you're not using them — which, with this sort of desktop interface, is most of the time. The second is the ability to freely resize windows. For some reason this doesn't yet apply to the 'parent' window, which remains minuscule, but as before, all of its components can be floated as separate panes, and these can now be made as large as you like. Another new feature introduced in this update is a switchable Mid-Sides matrix for channels 1‑2. This operates in the Input pane, so if you connect your Mid mic to input 1 and your Sides mic to input 2, then engage the matrix, what you get in the rest of the mixer and your DAW will be conventional left-right stereo.

As on the BlueBox Recorder, one of the best aspects of the Cello's built-in mixer is the master section, which includes not only the talkback, dim and monitor control available from the top panel, but additional functions such as mono, independent left and right output muting, and the ability to designate either headphone output as the PFL bus destination in place of the main outs — unusually, there are separate PFL and solo buses. There is potential for further improvement on the usability front — at present there's no way to link adjacent mixer channels, nor any easy way to make a channel's pan control jump to the centre — and JoeCoControl remains cheerfully idiosyncratic in its design, but it is clear, functional and succeeds in fitting an awful lot of control into a compact interface.

Cello, Is It Me You're 
Looking For?

Although it's not in the premium price bracket occupied by desktop interfaces such as the Prism Sound Lyra 2, the Cello is far from being a budget product. A glance at the specifications might suggest that there are rivals offering similar performance for less: Arturia's AudioFuse springs to mind, for example, as does RME's Babyface Pro. Thanks to its reliance on generic USB drivers, meanwhile, the Cello's low-latency performance can't match that of the custom drivers developed by RME, MOTU and Focusrite.

As a result, there are probably three things that will cause people to buy a Cello rather than one of its competitors. The first is its subjective sound quality, which is excellent all the way from the high-quality mic preamps to the headphone amplifiers. Second is its physical construction, which is both smart and seriously rugged; I would back the Cello to survive life on the road longer than most interfaces in its class. Finally, there are the unique and unusual features of JoeCo's design, such as the choice of converter filter shapes, the distinctive insert arrangements and the ability to capture audio at octo sample rates. This last might not be very relevant for conventional music recording, but it will be of keen interest to those sound designers who like to record ultrasonic sources and pitch them down into the audible frequency spectrum. And I think anyone who has a 500-series rack, or a couple of outboard units, will enjoy the flexibility of being able to split a mic input and record both processed and unprocessed signals. With the Cello, JoeCo are offering a characteristically individual take on the desktop audio interface, and the factors that mean it won't suit everyone will also make it perfect for some.


The Cello is a class-compliant USB audio device, and on Mac OS uses Apple's built-in Core Audio driver. As ever, this offers reasonable but unstellar low-latency performance, and the Cello is also burdened by the small amount of delay added by its build-in DSP mixer. At the lowest 32-sample buffer setting, Reaper reported a round-trip latency of 6.7ms; a loopback test showed that the true figure was actually a few samples lower. JoeCo's specs give a detailed list of round-trip latency measurements at different sample rates and buffer sizes relating to operation under Windows, and here, the lowest achievable round-trip latency at 44.1kHz is given as 10ms with a 32-sample buffer. On the plus side, this apparently falls to under 4ms if you record at 384kHz...


  • Sounds very good, with high-quality preamps.
  • Incorporates some unusual features such as 384kHz recording and the ability to choose different filter shapes for the A-D and D-A converters.
  • Insert points allow processed and unprocessed signals to be recorded to separate tracks.
  • Rugged build quality.
  • Built-in talkback, with comprehensive additional monitor control available in software.


  • Unspectacular low-latency performance.
  • External PSU cable is too short.
  • Talkback button transmits mechanical noise to the talkback mic, and only operates in momentary mode.


JoeCo have brought fresh thinking and some impressive engineering to the world of USB audio, creating a desktop interface that stands apart from the crowd.


£999 including VAT.