REVIEWS: Mike Sokol for Modern Recording




Stereo Opto-Compressor / Program Equalizer

By Mike Sokol  for Modern Recording -All Rights Reserved 3/25/00


APPLICATION: Stereo compressor-equalizer for mastering

SUMMARY: Stereo class-A vacuum tube compressor with twin signal path (with tube bypass) and variable attack/release times and ratios, opto-compressor design, and stereo six-band graphic equalizer utilizing discrete Class-A / passive design. Side-chain insert path with monitor/listen. Lots of muscle with a delicate touch…

STRENGTHS: This is one fine mastering tool in a box. You can change the signal path with the compressor pre or post EQ, and the analogue gain meter almost a work of art. Plus the signal chain has a hard-wire bypass for any function you’re not using at the moment. And it will accept signals up to plus 36 dBv….. which makes for some serious headroom.

WEAKNESSES: None that I could find….


Avalon Design has quite a reputation for mic pres, so they needed to really show their stuff on this box. Basically, the VT-747SP is a stereo mastering tool that combines a wonderful sounding optical element compressor using a class-A tube design, with a basic 6-band passive filter equalizer with fixed but intelligently selected frequency points. Being a true stereo unit, there’s no way to break it apart and use one side for mono vocals and the other side for bass guitar. But if you really wanted to, you could pass single tracks out to it one at a time during a tracking or sub-mix session, depending on how you like to do such things.

Housed in a sleek-looking 2-RU package, the VP-747SP does have a lot of copper and iron in the construction, so make sure you have someone help put it in the rack. And because it’s a class-A tube design, make sure you leave some ventilation above and below it. The up side is are no noisy fans to disturb the quite of your control room, but you do need to give it a little air to breath. Operationally, the left side of the front panel is the compressor section with all the functions you could want in a professional unit. The TSP switch switches in the tube path if you wish, or it can be eliminated from the signal path. Controls for attack and release times as well as compression ratios allows you to tailor the action of the optical gain element, and there’s a set of spectral controls for the side-chain, which can be used to zero in on a problem area such as vocal sibilance while leaving the bass untouched. And of course there’s a make-up gain control. A large meter dominates the center of the panel which indicates the amount of gain reduction taking place.

To the right of the front panel is a straightforward six-band equalizer and a stereo output level meter. A main output control and bypass switch round out the functions. The back panel has XLR connectors for the I/O, and a strap which can lift the power supply from the chassis ground, this being especially helpful in a rack with various grounding schemes.

Within minutes of unpacking the box, I decided it was time to light the fires (literally) and peruse the manual while all those little electrons got warmed up and began their speed-of-light journey from the cathode to the anode. (Hey Roger…. just how fast are the electrons actually traveling in a tube anyway??? I’m guessing it’s at the speed of light in a vacuum, but possibly the control grid bias and signal fluctuations change the speed as well as the density of the beam. But I digress.) Being in a hurry, I just pick a B-52’s CD off the pile and cued up Private Idaho. But while the equalizer section really worked well, the compressor function wasn’t happening for me. A quick mental (and meter) check confirmed that the song already had been squeezed to within a decibel of it’s life anyway, so it wasn’t appropriate material to judge compressor action. Back to the stack of un-mastered DAT which produced several candidates for level control. I had a nice Celtic piece with a beautiful image and tone, but which was way too low in overall volume even when the peaks were slapping zero. A little deft action on the compressor with some make-up gain and the song still had nice transient peaks, but the VU meters on my console went up by 10 decibels. Very nice…. Then I patched in the equalizer after the comp for a little final sheen on the top while taking out some obnoxious 5 KHz "presence" from the original mix. (Oops…. that was me mixing the tracks originally… what could I have been thinking?) A little bottom roll-off completed the sculpting and it sounded far better coming out of the box then it had going in. Remember, I was only doing 1 to 2 decibel changes… a finesse fix rather than a sledgehammer fix.

Now on to some "metal" tracks that I was supposed to "sledgehammer" into shape. Basically, the artists wanted the tracks to be as loud as (in?) humanly possible, but still fit within the 16-bits of a CD. Oh yes, the bottom in the mix was a little thin as well (don’t monitor on speakers with enhanced bass, or you’ll get thin mixes). I left the tubes in the signal chain in the path, added a few tweaks of the graphic equalizer to put the bottom up where it needed to be and folded in a little extra sizzle on the top. Since I was able to reposition the compressor after the eq section, I could go for massive-aggressive compression without peaking that sounded simply HUGE. Yes, it was a sledgehammer fix… but hey, you do what you gotta do.

To recap, like an iron fist in a velvet glove this box is capable of great gentleness most of the time, but can be called upon to deliver maximum "iron" when needed. I personally don’t like digital compressors, having gotten used to some great classic analogue boxes over the last few decades. (I collect what used to be called junk, but is now considered classic gear.) Call me retro, but I still like to twist the knob, watch the meters, and hear the action. I can’t used to setting compressor functions using a mouse, and even digital compressors with real knobs seem to run out of steam before I can get the job done sometimes. Computer plug-ins and wanna-be processors can be the flavor of the month, but you could buy a VT-747SP and count on it for 24/7 operation for the next few decades. And I don’t think you would ever get tired of it. Highly recommended.

Contact Mike Sokol with your questions and observations at or visit his new website We’re here (hear?) to believe you!

Mike Sokol
JMS Productions Inc.


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