The Rockruepel comp.two, designed and hand-built by Oliver Gregor in Germany, is the successor to the [Tape Op #86], released in 2011. The received excellent reviews, and surprised more than a few users with its pinup-girl- clad VU meters. The comp.two loses the pinup girls, but retains much of the classic look and design of the original unit. A two- channel vari-mu compressor, the comp.two's build follows a minimalistic approach with only six components in each channel's audio path: two transformers, two coupling capacitors, and two tubes. A 6 mm thick 3RU-height aluminum panel fronts an all-aluminum chassis containing premium, hand-wired circuit components from Elma, Alps, Sowter, and Hoyt, along with a custom toroidal power transformer and a unique complement of tubes. The front panel sports a vintage look, showing off two large, round VU meters and six well- spaced and neatly labeled knobs for each channel, along with toggle switches for mains power, individual channel bypass, and dual-mono or stereo operation. The only splash of color comes from Rockruepel's simple red-and-black logo. The rear panel simply sports XLR I/O for each channel and an IEC power socket.

So, here's another vari-mu tube compressor. I already have two of those, which both see daily use, but I was eager to see how the comp.two fits in with the pack. The comp.two provides controls for input and output gain; threshold; attack and release; a unique sidechain filter; and the option of stereo- linked or dual-mono use. The internal sidechain filter allows low frequencies to pass through the sidechain undetected, which adjusts how the compressor reacts to program material with a large amount of low-frequency energy. This high-pass filter can be set to flat, 50, 74, or 110 Hz; or the sidechain control can be set to "Amp Only," which turns off the compressor control and allows the audio to pass uncompressed through the amplifier's tubes and transformers. Pushing audio through the tube amplifier provides a certain amount of tube compression or even overdrive, while the output control can be backed off to avoid clipping devices down the line. The comp.two can provide up to 32 dB of noiseless gain, easily driving its output to over +32 dBu.

Typically, vari-mu compressors serve as mastering and bus processors, with their inherent moderate attack and release times and smooth compression ratios which increase as the compression increases. In addition to the traditional settings, the Rockruepel boasts some very fast time constants. The manual describes the attack settings range from 3.5-70 ms in ten steps, while the release ranges from 200 ms to 4 seconds, also in ten steps. In practice, it seems that the attack and release times relate to each other such that a very fast release time actually speeds up the attack time to well under 3 ms. These extreme settings provide a wide range of compression effects, ranging from subtle gluing to extreme distortion and pumping. Incidentally, the input and output controls are not stepped, but are continuously-variable. After watching Gavin Lurssen and Reuben Cohen "play" their processors during mastering passes, I can appreciate continuously-variable gain controls on mastering boxes. Furthermore, the knobs have a long enough throw over their ranges that I never felt like I couldn't fine tune the settings, or even quickly and easily match left and right input and output levels.

My first application of the comp.two took place while mastering an album for a local gospel artist. The album material ranged from guitar-based pop-rock to booming 808- driven urban productions, and I took the opportunity to compare the comp.two to two other vari-mu compressors: a Chiswick Reach, and a Summit DCL-200 modified by Steve Firlotte at Inward Connections. I immediately noticed that the Rockruepel has an extremely low noise-floor and a huge amount of headroom. I could easily overload the inputs of my A/D converters, even with the input and output controls of the comp.two barely in the top half of their range. Next, I noticed how easily I could dial in very effective compression settings thanks to the range of attack, release, threshold, and sidechain options. I could always find an attack and release that allowed the natural dynamics of the song to remain intact while still applying some overall glue to program. Playing the attack control against the sidechain's high-pass filter let me dial in settings that really helped hip-hop tracks keep their low-end clarity, punch, and sustain, while gently limiting the high frequencies and giving the overall apparent level a nice boost. The comp.two's minimal circuit path and Sowter transformers produced extremely open and clean low- frequency response and an extended and slightly enhanced high-frequency sheen. Conversely, my Chiswick Reach, with vintage Triad transformers, provides great low-midrange focus for hard rock drums, guitar, and bass, but sometimes smears low-bass frequencies, delicate high frequencies, and wide stereo details. The modified Summit, on the other hand, focuses vocals and pianos nicely, but with a leaner bottom end and also a slightly narrowed stereo spread. After a few minutes of playing around, I could easily guess which compressor would best suit a particular production. The comp.two could provide a much more pure and transparent compression than the other two compressors, as well as put some hair into a mix, if I pushed the input hard.

During some mixing, I put the Rockruepel to work on an electric bass track and found a huge variety of tonal options. The comp.two can easily add just a bit of size and roundness to a bass with only the amp engaged, or it can gently even out the dynamics with the compressor online. Surprisingly, the comp.two could also create all-out havoc, vicious distortion, and harmonic destruction with the (im)proper use of attack, release, and input versus output gain settings. I think Rockruepel pride themselves in the diverse sonic palette this compressor can produce. Similarly on drums, I could easily dial in a fat Fairchild-like warmth or generate some intense smack or rich sustain for a parallel drum bus. Electric guitar benefited from the tube saturation that could be dialed in, and just a touch of compression tucked the guitars into the track. My all-vocal bus always has a vari-mu across it, and the comp.two could easily fill that slot with its gentle sheen and slight overall glue.

All-in-all, the Rockruepel provides some of the cleanest tube compression I have come across, as well as some of the sickest overdriven tube processing you could ever want. This is truly a world-class piece of gear, worthy of a mastering studio or high-end mix room. Not many of us can afford its hefty price tag, but if you are in the market for a high-end tube compressor, this may certainly be the champ.

Tape Op is a bi-monthly magazine devoted to the art of record making.

Or Learn More