These days, fans of the much-loved (and much-misunderstood) Spectra Sonics 610 compressor/limiter (dubbed “Complimiter” by the company) have much to be happy about. In addition to the original model being readily available again (it was introduced in 1969, eventually becoming somewhat obscure, and then reintroduced with a few refinements in 2008), Spectra Sonics has just issued a lower-priced version — the 611-B — that differs a bit from its bigger brother.

For those unfamiliar with the original 610, it is unique among analog compressor/limiters in that the limiter circuit has such a fast attack time (100 nanoseconds — the fastest on earth that I am aware of), that transients can actually be tamed independently of peak-to-average ratios. When set correctly, the results are dramatic — much less distortion, better signal to noise ratio, and improved dynamic range. This is unusual, and very useful. It’s also a bit difficult to wrap one’s head around, frankly. Bill Cheney, co-owner of Spectra Sonics, explains it best, saying, “Most analog compressor/limiters operate as peak-sensing volume compressors. So, the gain of the device is determined by the peak-to-average ratio of the audio that is to be processed. For example, a peak-to-average ratio 10 dB above average audio program material results in approximately 10 dB of gain reduction for the device. Since the noise of a given audio system is generally fixed, the 10 dB reduction in device gain results in 10 dB increase in system noise. The higher the peak-to-average ratio, the larger the gain reduction, which results in a corresponding increase in system noise and significant loss of system headroom. The Spectra Sonics 610 and 611-B Complimiter designs employ independent limiting and compression functions, which may be used separately or combined. The limiter function eliminates the peak overload associated with short time-base transients. As an example, if a 10 dB peak-to-average ratio is present within the program material, the 610 and 611-B Complimiters eliminate the 10 dB peak overload component and allow the system gain to be increased 10 dB. The overload recovery occurs by virtue of the sub microsecond attack time exhibited by the 610 and 611.”

The cool thing about all of this is that, if set appropriately, the 610 exhibits very little sonic coloration, other than level control. It can be considered one of the highest fidelity compressor/limiters around. High frequencies are not smeared or muffled the way they can be with other compressors. The 610 “plays well” with other gear. That said, as a bonus, when the controls are set differently, say, with a quick release time and high input level, the 610 can overload and distort in a very pleasing, tube-like way. Think Tchad Blake.

The 610 is reasonably priced at $1595, but with the 611-B, Spectra Sonics has made it easier for budget-minded studio folks to get in on this singular type of compression/limiting. At about $950, the 611-B’s circuitry and behavior are identical to the original 610. The input transformers are different, though, allowing the 611-B to accept mic and instrument–level signals, as well as line-level. So, it can double as a direct box or mic preamp — a very handy bonus.

The front controls consist of an input pad, stepped from unity down to –24 dB in 6 dB increments; a release-time knob; and a slope knob. I’m not sure why Spectra Sonics opted to use the term “slope” instead of “ratio”. Definitely not a big deal; I quickly got used to it, but did initially find it confusing as “ratio” seems to be universally used for this type of compression control. Surprisingly, there is no gain-makeup stage in the 611-B. This had me scratching my head until Bill Cheney explained that he and partner Jim Romney decided to keep costs as low as they could by skipping the output gain stage. They felt that the extra gain would not be needed in most cases and, where it was needed, the user could use a third-party line amp or channel strip to add gain. When checking out the 611-B, I found this to be true. Only every once in a while — generally when using the unit as a straight-up channel insert — did I find I missed the extra gain. The company plans to release a companion to the 611-B, the M-101 preamp, that will effectively turn a 611-B into a full blown 610.

The 611-B is housed in a sturdy, smallish tabletop enclosure reminiscent of a high-end direct box. Very portable and good looking — black with small, chrome, front-mounted “D” handles — yet curiously non-standard. Cheney reports that Spectra Sonics has imminent plans to release a version in standard rackmount format, and that they did attempt to make the 611-B work as a 500-series module, but found the DC voltage supplied by a 500-series rack was too low to support the 611-B’s required parameters without a serious compromise to performance.

I enjoyed using the 611-B in a variety of situations and found its clarity particularly handy for controlling levels while tracking (where I didn’t want to necessarily color the sounds, preferring to save that option for mixing). With vocals, I found I could compress fairly heavily without ending up with mushy, essy artifacts — the natural high end remained sparkly. On the other end of the spectrum, I loved smashing drum submixes with the 611-B by boosting the input level and setting a fast release time. The resulting distortion and “tunable” pumping were cool aspects that helped give a somewhat limp drum performance a lot more teeth.

With its hand-selected components, top-notch build-quality, yet moderate price tag, the 611-B is an affordable way for anyone, from a world-class facility to a minimalist home recordists, to achieve the singular, versatile, super hi-fi sound and performance of a Spectra Sonics 610. It’s really not an exaggeration to say there is no other compressor/limiter like it, nor has there ever been. ($945 direct;

–Pete Weiss,

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

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