CharterOak SCL-1

Stereo compressor

CharterOak SCL-1 Stereo compressor

Review by George Shilling

CharterOak have been making boutique microphones since 2002. Endearingly, rather than boosting his ego, founder Michael Deming, (an engineer and producer of some note), named the company after a local Connecticut landmark. With a product catalogue comprising mainly exotic microphones, CharterOak have surprised everyone with this highly unusual stereo compressor, an early example of which I was lucky enough to try.

Flipping the far left toggle to On makes the large VU light up. The two channels’ controls are arranged above each other and each channel comprises seven pleasantly tactile knobs. These machined aluminium knobs are etched around the rims with a zero to 10 scale. They are smoothly damped, although a few of the knobs were snagging very slightly on the front panel of the review unit. CharterOak are already aware of the problem and now simply mount them slightly further from the front panel when the hex nut is secured.

At the far right a pair of toggles select between Dual and Stereo mode, and Metering of Channel 1 or Channel 2 Gain Reduction. In Stereo mode the Channel 1 controls become master, with the control signal derived from both channels. Input and Output gains sensibly always remain independent, allowing for precise left-right calibration.

The manual suggests fairly extreme initial settings as a starting point to help one understand the concept. Of course, I initially didn’t read this(!) and wondered why the meter was so far off zero. Firstly, the Input gain left of the controls should be set at full tilt, which provides the lowest noise floor, with the furthest right Output gain knobs needing to be set around 5 for 0vu output. The next knob is Static Threshold. This effectively calibrates the unit. It is recommended initially to set the unit to stereo mode and the metering to Channel 1, and tweak this knob until the meter settles on zero.

Lowering Static Threshold (clockwise) moves the meter past zero, providing a harder knee, (as when pushing all the buttons in on an 1176 - but less extreme, and continuously variable). Raising this (anticlockwise) gives a softer knee by creating less potential for swing in the control circuit, and simply setting it a dB or two below zero softens the knee. Next along is the more conventional Dynamic Threshold control. It is recommended to crank this to 7, i.e. a fairly low threshold. However, although the review model needed a fairly hot signal to enable a suitable threshold to be set, a couple of resistors’ values have been changed in more recent examples, allowing for 10dB lower threshold.

Attack and Release knobs are merely labelled 0 to 10 and work opposite to each other, so fast Attack is anticlockwise while fast Release is clockwise. These should initially be set fairly fast, then one sets compression Ratio. This knob varies continuously between 1:1 and 1:20, so setting it halfway at 1:10 is recommended. Having made these adjustments, with a little tweaking it was possible to see average compression of -6dB or more on the meter, and hear, well, very little obvious effect! The transparency of the gain reduction and the effect of the gain make-up in the circuit results in an astonishing smoothness and clarity. But comparing a section of program with and without the SCL-1, average perceived level was several dBs higher when utilizing the processing of the SCL-1 (when normalized), and a delightful, subtle overall glow was revealed. The subtleties of different settings gradually become apparent, but large changes frequently sounded fairly subtle.

The design brief was to achieve complete transparency, and Deming says it turned out even better than he expected. After 25 years of mixing without a buss compressor, he now has it hard wired across the mix. It is faster and cleaner than any other compressor I have ever encountered. There is always a measure of ‘auto’ recovery taking place, so with release set fast, dynamic material like pop music will make the meter waggle like crazy. The Auto circuit always releases to the constantly changing everage level, and this is what prevents any pumping or gasping.

The control circuit is effectively a discrete VCA circuit, with a control circuit governing the FET, which in turn goes to the gain cell. Cleverly, the circuit also makes up much of the gain automatically. However, this, and the lack of a bypass can make it difficult to tell what the SCL-1 is actually doing, such is the subtlety of the compression in some situations. There is no Bypass, but I understand that by request relay bypass is being planned as an option, (as is a mastering version with 11 step potentiometers). Even with extreme compression, the stereo image stays remarkably true, and there is no discernable loss of top end, a by-product which one expects with most compressors. I initially had the unit for a classical/showtune vocal and piano session, and used it for piano recording and again subsequently for mix buss where it proved to be the perfect processor for the job, invisibly and subtly reducing dynamics a little, without any discernable pumping or artefacts. In fact, I was way too cautious with the settings – it really is rather difficult to overdo things with the SCL-1. However, despite the transparency and lack of apparent distortion, there is certainly some enhancement audible with heavy compression settings.

Some impressive solidarity was noticeable in the low frequencies of a pop-rock mix when the SCL-1 was driven fairly hard. The unit offers a ‘soft symmetrical clip’, so the mix certainly cooks, while retaining much of the dynamic range. I did find the metering a little misleading, as it doesn’t take into account the subsequent gain make-up, so even if the meter is off the scale past -20dB, total gain reduction is rarely more than about 6dB. CharterOak are considering switchable metering to show net gain reduction at output, which I think would be useful. While there is some narrowing of the dynamic range, this kind of compression is generally too subtle for rock vocals. However, I did have remarkable success, making a dynamic vocal sit perfectly in a track by connecting the two channels in series using Dual mode, and using what would be fairly brutal settings on any other unit. The warmth, presence, size and microphone character shine through, and the vocal glows rather than sounding squashed.

The SCL-1’s philosophy has been cleverly executed, and this is a wonderfully unique processor.

Pros: Uniquely transparent gain reduction; excellent auto-recovery; clever gain make up circuitry

Cons: A few early-model niggles - all promised to be sorted; Too subtle for some applications

Reproduced with kind permission from Copyright ©

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