The V610 is an enhanced version of the classic Complimiter from Spectra Sonics. Spectra Sonics was founded by William G. Dilley in 1964 to build products for recording and broadcasting studios. Dilley was a WWII veteran and pilot, with countless accomplishments, including world speed records, command of top US Air Force units, and various Chief of Engineering roles for jet aircraft operations and ballistic missile systems. In 1969, he and his company debuted the Model 610 Complimiter, which came to be a standard dynamics processor found in top studios for years, but it eventually fell into relative obscurity. Then in 2008, the 610 was reintroduced with some refinements, and more recently, the lower-cost Model 611 Complimiter series [Tape Op #90] was introduced. As the name suggests, the device can serve as a compressor, a limiter, or both simultaneously. The heart of the unit is a solid-state dynamics module named the 601. One of the fastest analog limiting circuits in production, the 601's attack times are measured in nanoseconds - not milliseconds. It is no surprise that Mr. Dilley registered 14 patents and received numerous fellowships, awards, and accolades during his long and storied career. 

Last year, we wrangled a pair of Spectra Sonics M-502 units [Tape Op #90], which replicate the Record Plant New York's input/EQ preamp channel. Tape Op contributor Dave Hidek used them to track Jeff Gretz's drums for an upcoming Zao album. They finished a day early (Gretz is a beast), and I "appropriated" the units for mastering. Although the channel strips were not necessarily a fit for my mastering setup, the limiter's abilities intrigued me. I had never encountered an analog unit with attack speeds like this. In speaking with Bill Cheney [#102] at Spectra Sonics, he explained that the V610 was on the drawing board. Some time later, the review units came, and I started writing. 

Actually, that's not true. I tried to weasel out of this assignment. My email to the company went as follows: 

"Dear Spectra Sonics. I have received the review units for your soon-to-be released V610 Complimiter. I understand you wanted to know my schedule so you could ship the units to the next reviewer. However, I regret to inform you that I cannot return the pair. They are stuck in my signal chain, and I've investigated welding them into my racks. I'm prepared to offer you over-asking price for the units, provided I no longer have to submit the review to Tape Op. I'm hesitant to disclose to other mastering engineers what a beautiful game-changer the V610 is. Please let me know your thoughts on this. Take your time. I'm in no rush to finish testing." 

Unfortunately for me, my editors at Tape Op got wind of my scheme. So, here we are. And I have to tell you about the V610. As with lots of mastering gear, the controls are detented, allowing for precise recall. The unit has separate inputs to handle mic and line-level, and a single line-level output, each available on a standard XLR connector as well as a Phoenix Connect terminal block. Four setup knobs cover mic/line switching, polarity reversal, input pad levels, and phantom power. (Initially, I was concerned about adding a piece of gear with phantom power to my mastering chain. However, Spectra Sonics has this covered, as only the mic jack can see phantom power.) In addition to the recallable controls, the V610 has a lower noise floor than the original Complimiter, as well as a higher +24 dBU output. At three rackspaces high, the front panel has room for an LED gain-reduction meter that curves around the slope control, and a 3.5'' VU meter showing output level. A threshold LED illuminates if compression is occurring, while an overload LED warns of clipping. I should probably mention that the inclusion of phantom power means this unit is not a dedicated mastering box. In fact, many recording engineers are buying it for vocal and other tracking duties. As with the M-502, you can place the V610 between a mic and its preamp. The Spectra Sonics can provide 48V to your mic, you can crank the gain, limit and compress, and drastically change how you load the preamp. (You might want to re-read that.) In some ways, you get totally new sounds out of tried-and-true mic/preamp combinations. This is indeed a flexible unit. 

In use, the V610 is a "trust your ears" device as there are only a few controls. Compression is not a fixed value. It is a function of both input level and low-frequency content. So how hard you drive the unit in conjunction with the threshold/release controls determines much of the sound. As the threshold indicator becomes more constantly lit, more gain reduction will be shown on the LED meter. If the threshold indicator is only flickering and no gain reduction is showing on the LED meter, it means there is only peak limiting happening. The Slope control affects the amount of compression applied to the signal. Thinking about leveling amplifier designs, such as the venerable 1176, helped me in understanding how the Spectra Sonics circuit works. A higher value for Slope results in more leveling of the overall sound, while a lower value offers gentle rounding for peaks and stray transients. 

The Release control affects the compressor only, with values ranging from 0-10. The shortest time is counterclockwise at the 0 position. (The peak limiter, which operates independently, employs fixed 90 ns attack and 90 ns release times.) Sort of an "auto" mode, the release time is a function of both compression and the amount of low-frequency content. For example, a kick drum hit will result in a longer release time than a lead guitar note. For most situations, start in the middle and adjust faster or slower by ear. The math behind the release time calculation is in the manual. The unit will produce audible distortion when the release time is too short. In use, I tended to choose lower, more gradual slope numbers. However, more extreme settings are useful for certain genres and definitely useful in tracking situations. Recording a vocalist who can't work a mic and is all over the place? The V610 is an answer for that. But where I found the unit shines is at program limiting. 

Female vocals, piano, classical guitar, marimba, brass percussion, glockenspiel, trumpet - these are wonderful things to record. But they are also a rogue's gallery of harmonic offenders. I'm specifically referring to the tendency of any of these instruments to generate harmonics that are so powerful that they can lead to analog overload. I'm not talking about the original sound waves in the air; I'm talking about electronic junk that is captured and transmitted, outside of the human hearing band but within the operating limits of analog circuitry. In the mastering stage, when we start leveling songs and matching loudness across a record, one of these sounds can peak so powerfully that they go past the headroom of most analog units. And this isn't a poor tracking or mixing issue, this is a physics thing. Over the years, I've pestered some of the leading names in contemporary gear design regarding this problem. Most suggested backing down the level, giving the analog gear much more headroom, and making up any gain in the digital domain. While that workflow works to eliminate the distortion, it completely negates specific gain-staging I want to employ to take full advantage of the gear in my chain. Well, the V610 eats these harmonic gremlins for breakfast. Early on, William Dilley determined that these non-musical artifacts can be eliminated from the signal path. His 601 design does just that. To oversimplify, the 601 removes sub-microsecond voltage peaks from the music program material, which is the key to increasing the headroom (available dynamic range) while reducing overload distortion. In the past year, I've encountered over a dozen projects where such instrumentation blows past my analog gear's operating headroom. Patching in the V610 solved the problem for all of them. 

Spectra Sonics took a long time getting a pair of review units to me. It seems that any time a demo unit of the V610 made it into the wild, the tester refused to return it. Alas, I fared no better. But it was worth the wait. Indeed, I have been reluctant to disclose how much I enjoy my Complimiters. With improved noise specifications, easy recall, and a "trust your bottom dollar" peak limiter, I'm still in the honeymoon phase with mine - and this has gone on for many months. Contact M1 Distribution <> if you have technical questions or are looking for a nearby dealer. 

Garrett Haines is at

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

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