There is no doubt that Groove Tubes understands vacuum tubes. Aspen Pittman, the owner of GT, is one of the most knowledgeable persons you could ever meet when it comes to the subject. As a follow-up to their successful creation of the ViPRE mic preamp, Groove Tubes now has the variable transconductance Glory Comp.

So what is the Glory Comp? Let's start with what it's not first. It's not small. This is a 3U-height beast that really requires 5U of rackspace. Why? Because this compressor puts out some heat. Seriously, there are seven hard-working tubes inside, and they need ventilation. It also is not light-37 lbs! There's real iron, glass, and metal in there, and racking it up requires some rethinking of your rack. The unit ships with bracing that needs to be installed to properly support it, and you do need those braces.

The Glory Comp has that nice retro look with large, vintage-style knobs; simple, easy-to-read screening on the faceplate (white text on flat-black faceplate); and GT's distinctive round VU meter. It has all the expected controls for a compressor: input, threshold, attack, release, ratio, output, side-chain source, and side-chain EQ (LF and HF). With these controls alone, the Glory Comp has all the tools needed to use it as an accurate and musical compressor that sounds really great and is very quiet. But Groove Tubes did not want to build an ordinary compressor; they built an extraordinary compressor by adding some very interesting extra features.

The first is a switch that selects the way the release time behaves. You can choose either logarithmic or linear curves. In logarithmic mode, the Glory Comp behaves like an opto- controlled compressor with a nice slow release that helps keep the program material from rising up too fast between incoming program peaks. Great for bass and vocals. In linear mode, the release time tracks more quickly and evenly and works better for more percussive instruments like acoustic guitar and piano. This switch alone creates the added value of the Glory Comp by allowing it to be two different compressors, and I found it to be a great feature, especially while mixing vocals. I'd get the vocal sitting pretty good in the mix using the basic knobs on the input side (attack, ratio and threshold), and then by experimenting with the release time and the slope selection, I was able to really control the output dynamics and get the vocal really on top of the mix without sounding squished to death. There is no doubt the tubes are a big part of the huge sound you get, but the well- thought-out control features make this more versatile than your standard two-knob tube compressors.

But the fun does not stop here. With the addition of the built-in side-chain EQ, you can control how the Glory will react to the program material coming in. The side-chain EQ knobs help shape which frequencies the compressor will react to. On a male singer up-close on a large-diaphragm mic, there was noticeable proximity effect and some plosives. With a turn of the LF knob, the Glory reacted much more strongly when some of the singer's low-end energy swelled up. It was like someone was riding the bass shelf knob on the channel, and it worked great. Later, while tracking acoustic guitar, I used the HF knob to adjust the way the Glory reacted to the pick drive and sleeve noise on the guitar. By raising the HF knob, you can make the compressor react and quickly attenuate the strident part of the signal while the good stuff passes through. Neat! I found the frequency choices (50 Hz and 10 kHz) to be musical in terms of how the compressor reacted. Of course, you can also set the unit to external side- chain and hook up your favorite EQ.

Finally, there is the knob that bears the compressor's name: the Glory knob! This knob is marked "Earth" on the far left and "Heaven" on the far right. What does it do? To find out, I went to the well written manual: "The Glory Effect essentially consists of special circuitry whereby low-order even harmonics are produced, over a limited band of frequencies, and intentionally added back to the compressed signal in amounts deemed by the user to be appropriate for the sonic events at hand. The harmonic bandwidth is confined to operate on signal fundamental frequencies from 40 Hz to 700 Hz." The manual goes on to explain that the circuitry "manipulates the signal so as to produce even-order harmonics only, predominately second order."

This knob is the real wild card on the unit. It works best on single sources, and I found it really added some depth to electric rhythm guitars. I also found that it was great for expanding the bottom end of the bass, although I did not add any "Glory" until mix because I get enough extra low-end love with my 2'' tape machine as it is. The key word from the manual is "appropriate," and that is where you get to twist away and decide how much is right for you. Personally, and probably because of the 2'' running 16 tracks at 15 IPS, I stayed closer to "Earth" most of the time. But I did use the compressor on some Pro Tools tracks, and I found myself reaching more towards "Heaven" to get the vocal sound I liked.

I've had the Glory Comp set up next to my mixer now for over a month, and in that time, I've used it for tracking bass, acoustic guitars, piano, and electric piano. The more I've used it, the more comfortable I've gotten with how it behaves. This is a solidly-built, professional compressor that has quickly found a place in our recordings. I love the way it places vocals in the mix. This compressor is very flexible and most importantly, musical. Groove Tubes has really built a classic compressor that reaches back to the great tube compressors of yesteryear for inspiration but has the modern parameter controls expected in today's electronics. At around $2800 street, the Glory Comp is a real bargain when you consider that its tube design and flexible release features make it two different compressors in one unit. How they got all of that to work with no IC chips is pretty amazing, but then again, when it comes to tubes, Aspen and the folks at Groove Tubes know what they are doing. ($3499 MSRP;

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

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