Side-Chain Envelope Follower And Filter

The KH-COMP1 has an especially designed envelope follower circuit to develop the side-chain control signal. For side-chain equalization there are two rotary controls called Low Edge ranging from Off to 1kHz and Hi Edge ranging from 2.5kHz to Off; each has their own variable Q controls with values ranging from 0.71 to 1.41.

There is an interesting switch called F.INV and when enabled, inverts the operation of the both side-chain filters together. Low Edge normally is a typical high-pass filter but when inverted becomes a low-pass filter. Hi Edge inverts the same way--normally a low-pass filter but becomes a high-pass filter when inverted. It is easy to hear these filters' actions using the Listen button.

Interesting to note is that the corner frequencies--the frequency at which filters start changing the sound is not consistent--the same when inverted. They both start out as approximately 2nd order filters and the separate Q controls change the filter's action in either normal or inverted modes. Apart from individually switching the frequency controls to the Off position, there is no master side-chain filter on/off switch.

Four Detectors

Another interesting and unique feature of the KH-COMP-1 is the choice of detectors. There are four detector modes starting counter-clockwise with RMS--aka average (root-mean-square).

RMS is a common method to develop a side-chain control signal. I liked RMS for compressing bass guitars--it was easy to keep the level constant without loss of the deep bass (notes) frequencies. For a five string bass, when the open low B string was played, the KH-COMP1 did not over-compress it. The Low Edge was set at 100Hz in normal mode and it was very precise in obtaining whatever I needed to keep that low string "in the house" with with the other strings on the instrument.

Vintage is the next detector mode and using it along with the Knee control set over to the Soft side worked great for a stereo-recorded Rickenbacker 12-string electric guitar. I used a 10:1 ratio and kept the finger picking arpeggios upfront and dynamically still! An awesome sound!

The third detector mode is called Peak. I hate that typical squashed snare drum sound I hear on almost every song out there! Using Peak, 2:1 ratio, hard knee, 19-ms attack, 140-ms release and inverted side-chain filters set to 45Hz and 3.1kHz, I was able to get a realistic and natural snare drum sound from a mix of five snare drum tracks (top, bottom, and three samples) so that it didn't "pop" annoyingly--just a louder snare drum with more sustain and the drum kit's ambient space.

Hilbert Transform Detector

The fourth detector mode is called Hilbert--shorthand for a mathematical technique called the Hilbert Transform. The detector's purpose in a compressor/limiter is that of an envelope follower. It must accurately track the input signal amplitude's changes exactly. "Tracing" the rise time shape, sustain period and expiry timings of the signal exactly but with minimal added latency and distortion are its goals. Using a Hilbert Transform-based detector creates an envelope follower with near zero-latency and super fast, accurate detection. Hilbert is the default detector mode in Black Rooster's KH-COMP1.

Hilbert detector mode works great on everything! I like it on harmonically rich instruments--it sounded great on a (real) 9-foot Steinway grand piano recording playing block chords and assorted filigree--in a Pop ballad. I wanted just subtle control at 2:1 with the gain reduction meter only occasionally moving.

Other noteworthy features include; variable stereo link control that sets the amount channel interaction from dual mono or no linkage at all to full stereo linkage and the variable compressor knee control that ranges from Soft to Hard knee. I am learning that variable Knee is super-important for aggressive compressor usage.

I don't know how they do it but the KH-COMP1 is a zero-latency compressor and I checked in my Pro Tools HDX rig at 96kHz by putting in 100 stereo instances none of them read any delay compensation!

The Black Rooster KH-COMP1 is available for $139 downloadable. Once I understood the technology, I found it to be a remarkable compressor perfect for any use because of its versatility.

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