Spectra 1964 - Model C610 Compressor  From Spectra

In 1969, the Model 610 Complimiter was unveiled, a revolutionary audio compressor and limiter.  Unique to this design was its ability to peak limit and compress audio separately.  At the heart of the Model 610 were the 601 Compressor/Limiter module and 101 amplifier circuits. The Model 610’s low noise floor, ultra-fast peak limiting and intelligent compression response made it an incredibly versatile unit and earned its status as a classic studio compressor.  For decades the Model 610 could be found safeguarding levels to tape, strapped across the mix bus, and even before record lathes in some of the most well known recording studios in the world.  

With the fastest peak limiter in the world and a compression attack time around 100 nanoseconds, the Model 610 Complimiter was the first device of this type to eliminate compression pumping and the need for de-essing, while maintaining full bandwidth at ratios of up to 100:1. In addition, the 610 is one of the few, if not the only device of this type, that rivals the best microphone preamps in terms of noise and distortion. Combined with an input threshold of -40dBu, the 610 offers the user the best of all worlds; peak-free transients, adjustable compression, low noise and distortion, and considerable amplifier gain.  

The Model C610 is the based on the original 1969 version of the Model 610 Complimiter. From the custom anodized aluminum knobs and black trimmed vu meter, to the internal discrete circuits, the Model C610 represents what made Spectra an industry standard.

The C610 utilizes the same operation format as the original with the addition of a third switchable meter setting, as well as 80/240 50/60hz VAC operation. The hand-built modules are made and tested in the same manner as the original 1969 version. The quality of materials used in the processes of building the Model C610 remain the same as before. This build quality of all Spectra 1964 products is an important hallmark, which results in the long-term value of this unique technology.

50 years after its release, the Model C610 has specifications that go unrivaled in today’s industry, proving Spectra founder William G. Dilley was decades ahead of his time.  And now, a new generation of engineers is discovering the Spectra sound for themselves.

From the original Model 610 brochure, ca. 1969:

“Spectra introduces the Model 610 “COMPLIMITER,” the newest proven concept in a rack-mounting compressor/limiter system with performance both measurably and audibly discernable as “beyond state of the art.” This unit performs the functions of peak-limiting and volume-compression, either independently or simultaneously, as a direct function of the type of program input, with performance that is unequaled by most linear amplifiers. The extremely low noise characteristics of this unique, self-contained system provide a very low threshold of -40dBm, thus allowing the greatest input sensitivity and compatibility with audio equipment and accessories used in the professional recording, broadcasting, motion picture and sound-reinforcement industries.

As the fastest of all peak-limiting devices (100 nanoseconds to 2 microseconds), peak-limiting can be employed with no audible distortion of any kind, thus allowing undistorted recordings, transmissions, etc. at average levels significantly higher than conventional “0” VU (+4dBm or +8dBm) while simultaneously providing maximum amplitude protections. A white threshold indicating lamp provides the audio engineer – for the first time – a representation of the peak-limiting taking place without the task of monitoring an auxiliary oscilloscope. A separate red overload indicating lamp forewarns the operator, in advance of overload, exactly when to check his control adjustments without requiring his undivided attention. The continuously variable compression/limiting ratio assures the widest range of slope control available from 1.1:1 (approximately linear amplification) to approximately 100:1 (flat slope, maximum amplitude protection line). Coupled with a constant threshold attack level of -40dBm, the need to continuously reset input levels during operation for each new compression/limiting ratio is eliminated. Variable release time control allows the selection of the smoothest dynamic action commensurate with minimum distortion (typically less than 5/100ths of 1%). The uniform frequency response of this unit negates the need for “de-ess” roll-off on all high frequencies.

During actual listening, the absence of noise, distortion, and frequency discrimination is readily apparent. The Model 610 “COMPLIMITER” is particularly effective in controlling sibilant sounds, restricting extreme ranges, and providing the smoothest dynamic action.”