Your browser is out-of-date!

Update your browser to view this website correctly. Update my browser now


SPL Crimson Interface: 6×6 USB I/O, Monitor Control, Great Sound

When SPL unveils a new product, it is often built around a one-of-a-kind new circuit. The company is probably best known for its Transient Designer, which allows the manipulation of attack and sustain in ways that sound and behave very differently than a traditional compressor does.

When SPL unveils a new product, it is often built around a one-of-a-kind new circuit. The company is probably best known for its Transient Designer, which allows the manipulation of attack and sustain in ways that sound and behave very differently than a traditional compressor does. Other patented processors like the Vitalizer, a tool for adding loudness and clarity, exhibit similar thinking. Meanwhile, when SPL steps into the arena of building more traditional circuits like mic preamps and EQs, they seem to apply their knack for creativity and still come up with an entirely new approach to a classic idea. The Crimson is an audio interface/monitor controller that echoes innovations from earlier SPL products, but combines them together in a single powerhouse of convenience.

Audio Interface

The audio interface portion of the Crimson is recognized by DAWs as a 6-input/6-output device. Neither Windows nor Mac OS X require the installation of an additional driver for operation, though driver installation on Mac OS X circumvents the Mac Core Audio Driver whose maximum sample rate is 96 kHz, and allows high sample rates of 176.4 kHz and 192 kHz. Along with the higher sample rates, the alternative HAL driver uses the Crimson’s clock, rather than the Mac’s internal clock, to time samples. Using either driver, there is no software control panel for the Crimson, as the integrated monitor controller carries out all monitoring considerations.

The audio interface can record signals from up to four analog inputs, which can accept signal from a variety of different connection and signal types. On the back panel, there are four balanced TRS inputs, each of which can feed the A/D converter to the DAW. These inputs have no additional controls for level adjustment or filtering, so those considerations must be made prior to feeding signal to these connectors. Either or both of the third and fourth A/D converter inputs can be repurposed to accept instruments connected to the pair of front panel ¼-inch jacks. Each jack has an associated gain control on the top panel of the unit. When an instrument is connected, the Crimson automatically switches from line input to the instrument input.

Crimson’s connections allowed me to connect instruments with low-output pickups and add gain to them up to healthy signal strength without adding noticeable noise. Likewise, I could attach guitars with hot or active pickups and there was always enough headroom. It’s quite stifling to the creative process and damaging to tone when devices have instrument inputs that don’t provide enough headroom and frequently distort, need padding; or require backing off the instrument’s level controls. You spend more time managing levels than actually recording. This couldn’t have been further from the case with the Crimson.

While the last two inputs trade between instrument and line connectors, the first two toggle between line and mic. The preamps are similar to the SPL GainStation in that they feature a discrete design with a single transistor per channel, rather than a cheap, typical, integrated circuit. While the GainStation’s preamps operate on SPL’s high-powered 60-volt rail, the Crimson’s pre’s feature a dialed-back 34V (±17V) rail. This is on par with well-respected high-end mic preamps, and unheard of in desktop audio interfaces. The benefit of running at a higher voltage is that the internal electronics exhibit more headroom, allowing even hot signals to stay as clean as possible before A/D conversion.

The Crimson offers a pair of S/PDIF digital inputs and a pair of S/PDIF outputs through RCA-type connectors. I didn’t have the proper adapters to test this, but they are said to be compatible with AES3 signals in addition to S/PDIF signals. While the third stereo output pair in a DAW or AMS is routed directly to the digital output, the four D/A-converted outputs return to the monitor controller and can be routed to physical connectors from there.

Advanced Monitor Control

Typically, when doing tracking sessions requiring much processing power, it becomes necessary to increase the buffers for A/D and D/A conversion. When this happens, the artists will hear themselves at a delay in their headphones. This is particularly evident when working with USB and FireWire interfaces, and even more so when working with the Core Audio driver on the Mac OS. Each step of the signal chain—from an analog connector to the DAW and then back to an analog jack—takes some amount of processing, and thus incurs some amount of delay.

To avoid this, some USB interfaces have a simplistic blend control to determine how much pre-converted immediate analog input signal versus how much software return will feed the headphone jack. Other USB interfaces feature more complicated software mixers to build balances of input signals and various software returns. The problem with these software mixers is that they usually use a large window that occupies a lot of on-screen real estate, and toggling in and out of your DAW to make changes is a little clunky. Also, they are summing signals in the digital domain, which can impose limitations in headroom and fidelity. The Crimson’s monitor controller employs a colorless analog circuit path for building headphone mixes, not to mention that you rarely will find the number of physical controls to build these mixes that you find on the Crimson. Ergonomically, this made such a huge difference, making everything quicker and keeping sessions from ever breaking pace.

Versatile UI

What’s great about the Crimson’s monitor controller is that it doesn’t lock the user into one particular workflow. Some devices have more of a 1:1 ratio of functions to connectors. Here, SPL seemed to try to serve musicians, DJs and audio engineers alike. The manual provides detailed setup diagrams for tracking, mixing, mastering and connecting various outboard devices.

Looking at the back panel, you see plenty of I/O, including a pair of balanced ¼-inch connectors, a pair of unbalanced RCA-type connectors, and an unbalanced stereo 1/8-inch mini jack. The balanced connectors can accept stereo signals, but if only the left one is connected, the signal is fed to the monitors in redundant mono. The left balanced input can alternatively be used for a talkback to the artist monitor path. There is no mic preamp in this circuit, so the mic must be preamplified externally.

Outputs include a balanced stereo pair of XLRs and another balanced pair of ¼-inch TRS connections. An “A to B” button takes the main mix and plays it through the secondary speakers instead of the primaries. Meanwhile, an “Artist Mode” button sends an entirely different mix to this pair of outputs to be used when connecting to an external headphone amp to feed multiple artists.

In Artist Mode, the first two outputs of the D/A converter feed the main monitors. The secondary monitor mix is fed by outputs 3 and 4 of the D/A converter, which can be carrying a unique mix from the DAW, plus a combination of other signals. Any or all of the four recordable inputs, plus any of the external sources can be added to the D/A-converted DAW returns through an analog bus. On top of that, the digital input can be D/A-converted by the Crimson and added to the analog mix feeding the secondary output. I found the lack of bleed when the switches for each of these signals were disengaged to be very impressive. In addition to those switches, there is a knob to adjust the blend of the recording inputs versus the software and hardware returns.

The two onboard headphone jacks can be fed different mixes and each has its own level control. All of this switching made building artist headphone mixes very simple. If Artist Mode is disengaged, all of the selector switches and blend control build the mix to feed the main monitors. That way, you could hear the artist mix through your headphones or monitors, make changes, and then feed it back to them. SPL also outlines a lot of creative ways to use the Artist Mode to send alternate signals to outboard devices and return them to hardware inputs. Aside from being stereo-only, I can’t imagine anything more that I would ask from a monitor controller than what is provided here.

In Use

Before using the Crimson for any kind of recording, I spent some time with it as a monitor controller. I cabled it into my monitors and Mac and tried to avoid referencing the manual, just to get a sense of how intuitive it would be. I spent a good amount of time hitting buttons before I heard anything, and it wasn’t until I looked at the manual that I was really able to wrap my head around the wealth of functionality. Once I understood just how many options for signal flow were offered, I came to appreciate the layout and could certainly justify the labeling and controls provided.

I really liked the feel of the big volume knob, but what I liked even more was that it was very accurately labeled in increments of 1 dB or less throughout the typical operating range. For calibration purposes, this was fantastic. I was really impressed by the overall sound of the D/A converters. They were clean, quiet and transparent, and the gain control was equally clean and colorless. I plugged in a guitar, and when combining the input signal with a DAW return everything remained very clean and clear, suggesting that the analog summing amplifiers were offering an appropriate amount of headroom.

After stopping playback, I noticed how great the instrument input sounded. The highs had a good amount of detail without seeming hyped and unnatural. The lows were big and tight, and at high or low gain settings they sounded equally present. Some circuits tend to make bass sound a little weak when dialed back too much, but this was not the case with the Crimson. There was also an incredibly low noise floor. This made me want to try out the mic preamps recording quieter instruments, which had forced signal-to-noise battles in the past. I got to work recording ukulele and was really amazed, in the first place with how much gain was available at the pre, but in the second with how quiet the pre’s remained even with a great deal of gain applied.

I had a similar experience when recording flute. I got everything set up and cabled in, made tracks in Pro Tools, and then started turning up the pre’s and heard nothing. I thought something was set incorrectly and then the flutist moved her music stand and I heard it loud and clear. The pre’s were just so quiet that it sounded like they were muted. Not only that, but the recordings were so real and true-to-life. I was truly shocked when I finally looked at the price tag. These pre’s sound like they should cost more than the entire unit does.

Worth the Wait?

The monitor controller is fantastic, and could easily fill the needs of anyone tracking, mixing or mastering in stereo. The preamps could easily be my favorite that I’ve heard on any desktop interface. If you’re in the market, you could spend a little less on a 6×6 audio interface, but the quality will definitely suffer. You won’t find anything so carefully designed for the serious professional at a lower price tag. If you’re shopping for an interface with a few choice inputs and a clean way to monitor, this should be high on your list.

Brandon Hickey is an audio pro and rabid Blackhawks fan.

Product Summary


PRODUCT: Crimson

PRICE: approximately $675 street

PROS: Tons of features, especially for the price.

CONS: Monitor controller doesn’t offer surround sound.

Try This

Try using the Crimson for mastering with the bx_control plug-in as an M/S encoder/decoder. On the plug-in, set “In” to “L/R” and “Out” to “M/S.” Send the track to outputs 3-4. Turn on Artist Mode to feed this to the second pair of balanced outputs. Use a more severe compressor on the left channel to crush the vocals, kick and snare, while taking it easier on the right, containing wider stereo signals. Return through line inputs to a track feeding outputs 1-2 with the opposite settings enabled on another bx_control plug-in then listen to the result through the main monitor output.