Pendulum Audio OCL-2 Electro-Optical Compressor/Limiter

2 reviews for Pendulum Audio OCL-2 Electro-Optical Compressor/Limiter

1. 

   Eddie Ciletti’s – June 19, 2017

   Eddie Ciletti’s review of the OCL-2 Tube Compressor in EQ

   Quite literally “out of the blue” comes a new line of products from a company that once made ‘only’ an acoustic guitar preamp. The OCL-2 is an optical compressor / limiter with a minimal, Class A signal path consisting of two tubes per channel. It is so minimal, that there are no input or output transformers even though XLR connectors get you the old ‘in-out.’

   The beauty of working with the OCL-2 as well and with its designer, Greg Gualtieri, is that both are remarkably open and flexible. Translation: There are a number of options, including balanced I/O and passive side-chain EQ filters. Mastering engineers and tweak heads take note: many of the control pots can be ‘customized’ to reflect user preferences such as Attack and Release ranges.

   After an extensive interview, I learned that Mr. Gualtieri’s design philosophy is derived from his need to capture acoustic guitar in the most transparent way possible. He is, however, not so much of a purist as to scoff at compression. Classic vintage signal processors are not always clean enough – nor are they in such great condition after time and abuse to justify current market prices. Greg originally created both the OCL-2 as well as the 6386 Compressor / Limiter for his own personal studio.

   Weird (But Cool) Science

   The Pendulum OCL-2 is not a clone of the Teletronics LA-2A. As a former physicist for Bell Labs, Mr. Gualtieri knows how a photo resistor works at the molecular level having devised a proprietary method of taming the unruly optical beasts to a previously unattainable level of consistency. As such, the OCL-2 inspires confidence as a stereo unit that no other optical unit can match and then some.

   It is hard to make traditional optical limiters sound bad. Without Attack and Release controls, users are limited to the natural characteristics of the optical parts, which just happen to be perfect for voice, guitars and bass – gentle enough to massage a stereo mix but not damage it. Other modern optical boxes like the Joemeek have added Attack and Release controls that go beyond normal to create interesting near-backwards effects. The controls on the OCL-2 are more effective (without the effect), in part because of the proprietary tweak that only Pendulum has.

   A LA Mode

   Science aside, the OCL-2 has a three-position MODE switch – labeled FAST, PRESETS and MANUAL. The first two preset disable the Attack and Release controls. FAST is as FAST does. In this mode, the OCL-2 gets about the most sonic agility possible from an optical device.

   Four of the Six PRESETS were originally modeled from the popular Fairchild Limiter. The last two presets are ‘Program Dependent’, which is to say that their response is more akin to a human ‘riding the gain’ and so less obviously processed. MANUAL mode turns on the Attack (1mS to 40mS) and Release (.1S to 2S) controls.

   How Fast Do You Want It?

   A VU Meter can indicate apparent ‘loudness’ better than a bargraph-style Peak Meter (unless the latter can simultaneously indicate peak and average levels). Instruments such as voice and bass have a nearly identical peak-to-average ratio, a perfect match for accurate display via VU meter. (The exceptions would be ‘P-popping’ consonants and ‘snap happy’ electric bass strings!) Conversely, transient-intense instruments such as drums and tambourine might deflect a VU meter only as high as ~5dB, but the peaks can be 10-dB to 15-dB higher. Analog tape machine users learn this lesson very quickly!

   On The Road

   The OCL-2 was evaluated at the same time as the Pendulum 6386 Tube Limiter even though the two reviews appear in separate issues. (See the 6386 review in the December 1999 issue). The units were daisy-chained along with a Great River transformer-less mic preamp and the TASCAM DA-45HR 24-bit DAT recorder. I was completely comfortable using them together with no fear of signal degradation and so thankful for the BYPASS switches, which are not common on vintage products (and even some modern units). Having both units in the signal path made the comparison of identical settings quite easy. With slow attack and fast release the two models behaved as twins, but in FAST mode, the 6386 is more responsive.

   Getting With The Program

   Stereo program was the first signal passed through the OCL-2 because that is my acid test. Pass the test and you know the unit can handle individual tracks with ease. The LA-2A and the LA-3A were most notable for their transparent approach to dynamics processing. The OCL-2 goes two steps further by being more sonically transparent (no input or output transformers on a ‘stock’ unit) and far more versatile in terms of Attack and Release parameters. This will be of particular interest to those who wish to capture vocals, or any acoustic instrument, with the least amount of added color while still having equally transparent control over dynamics variations.

   With the luxury of having the two models at the same time, I set the OCL-2 for a Slow Attack and Fast Release (my personal default) followed by the 6386 in FAST mode (as a peak limiter). My heavy-handed visuaî setting for the 6386 had lots of meter movement in Gain Reduction mode. To fully appreciate the FAST mode, however, more conservative settings of less than 1-dB of meter movement (2dB for the OCL-2) yielded such a profound sonic improvement that the 6386 review served as my VU meter refresher course. The combination of both units on a stereo mix was killer. (And this is as close to ‘born again’ as I will ever be!)

   Flat, Cool Head

   Unlike the LA-2A (and especially the ADL clones), the OCL-2 has a very flat detector circuit, which means the unit equally processes ALL frequencies. One approach is not better than the other although I personally prefer a weighted detector circuit, one that ‘hears’ in a similar non-linear way to the human ear. (Through experimentation with side-chain equalization, I have found that a broad 6-dB boost centered at 2.5kHz works well for many applications.) Pendulum sells a TRS side-chain insert plugs with a passive RC network customizable to a user’s needs. Very Cool!

2. 

   Mark Frink’s – June 19, 2017

   Michael Ross’s review of the SPS-1 Stereo Preamp in Guitar Player

   Why the world needs another optical compressor remained a mystery until I tried Pendulum’s OCL-2. I used the two-channel OCL-2 as a vocal compressor on several gigs that I mixed, including John Prine and several dozen bands at the Portland Blues Festival the following week.

   Especially common to live sound, VCA compressors achieve accurate compression ratios and well-defined thresholds. A chart of a VCA’s response shows a 45-degree slope, a bend at the threshold of compression and a second, flatter straight line whose slope is determined by the compression ratio. Many VCA-based compressors have enjoyed success with soft-knee features that allow a smoother transition into compression, illustrated by a rounding of the intersection of these two slopes.

   An optical compressor uses a photo-attenuator, whose resistance changes with the light intensity, but cannot respond as quickly as the light. Vintage models like the LA-2A use an electro-luminescent panel shining on a light-sensitive semiconductor. The classic soft-knee response is a result of level detection from this circuit’s output (feedback detection), instead of the input (feed-forward) detection used in VCA compressors. Unlike a VCA’s clinical compression slope with a fixed ratio, the response of an optical compressor moves through a soft-knee at threshold, reaches a plateau of compression at the target ratio, and gradually makes a transition to higher ratios of compression at its extremes. As a signal leans into it harder, these increasing ratios add a ‘density’ to the sound that is pleasing to the ear.

   The Pendulum OCL-2 uses a proprietary method for enhancing the response of a modernized version of this mechanism, providing faster attack and release times than are available from traditional optical compressors, and offering unrivaled transparency in its fastest settings. I usually find optical compressors a bit dull and woolly for live sound, where clarity and presence are paramount for lead vocals to stand out in the mix, but the OCL-2’s performance on vocals is bound to earn it a place in the outboard rack of top tours. On its first outing, the Pendulum’s open, clear sound earned many compliments, with an almost embarrassing series of audience members lining up to compliment the sound at the end of the show.

   In the Fast mode it performs a peak averaging of the signal, offering a very open sound. This is the setting for live work, and is even faster than the unit’s fastest manual settings. Six other presets, generally destined for studio applications, are similar to those found on the original Fairchild compressors. Four presets have increasingly slower attack and longer release times, with each letting a little more dynamic range punch through than the previous. Preset 5 has a program-dependent release time emulating the LA-2A’s two-stage release. Preset 6 is also program-dependent, but with three release stages. Both of these presets are useful for full-program mastering or vocal tracking, where the engineer doesn’t want the compressor to “suck back to zero” immediately to reduce pumping or breathing.

   The optical compressor section is followed by a class A, transformerless tube amplifier. Class A circuitry, of course, eliminates the cross-over distortion found in push-pull output stages, and the omission of a transformer offers an uncolored signal. The OCL-2 can be optionally ordered with Jensens for applications where galvanic isolation is desired. The transformerless OCL-2 reviewed was unbalanced, with both quarter-inch and XLR connections, but it worked problem-free with standard balanced insert cables.

   The OCL-2 also has side-chain access on a TRS quarter-inch jack, for inserting an EQ to allow frequency-tailored compression. Pendulum also supplied 6 dB/oct. high-pass filters cleverly built into the back-shells of TRS jacks to take advantage this “open architecture,” reducing the proximity-effect dominance of the compressor’s action in close-mic’ed live vocals, and opening up the compressor’s sound further.

   With large VU meters, this blue-faced two-space unit has the classic look of it’s genre. These hand-built gems employ poly caps, metal-film resistors and single-sided audio PC boards. When turned on, the tube’s power supplies gently ramp up to extend their life, and after taking a couple of minutes to warm up, relays un-mute the outputs.

   Though the name Pendulum remains a closely-held secret, the exquisite craftsmanship in the OCL-2 is reminiscent of their audiophile SPS-1 acoustic instrument pre-amps, which have found their way into the racks of top players like James Taylor, Leo Kottke and David Wilcox for years. Two other offerings were also introduced at the last AES show: the MDP-1 Tube Mic/DI Preamp and the 6386 Variable Mu Tube Limiter. This year designer Greg Gualtieri can be found at AES booth number 1345 in New York. – Mark Frink