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First developed by David Blackmer of dbx Inc., the original dbx 202 “Black Can” VCAs, can still be found in operating consoles today. These first VCAs suitable for pro audio equipment were built with a gain cell of eight discrete transistors. Later development of these IC’s surpassed all inconveniences of earlier designs, now rendering superior performances. CompIQ series of compressors use THAT Corporation Blackmer^® VCAs which are characterized by an exponential control characteristic (gain varies directly in decibels), extremely wide dynamic range, and low signal distortion. They are particularly neutral in sound, adding little or no coloration to audio signals.

Invented by David Blackmer of dbx Inc., the RMS-level detector computes Root Mean Square level of input signals in a logarithmic form, similar to how human ear perceives sound. The sound envelope decoded by this accurate detector is used to apply dynamic processing of the sound – the variation of signal level precisely controlled by the VCA according to parameters set by the user (Ratio, Threshold, Attack, Release, and Gain).

The threshold’s 50dB of range is designed to accommodate very weak signals up to pro audio level signals. The +4dB pro signal line level is at the top of this range, and consequently at the far clockwise end of the threshold knob. This gives a huge amount of headroom for the instrument’s generated signals, which ensure the compressor is not distorting with high-level spikes. We didn’t want that, by design. Some other compressors distort a lot, for various reasons, and headroom (or lack of it) is one of them. The CompIQ line of compressors is made to accommodate either lower OR hotter signals, and that is the reason why it can also be used with synths or other line-level devices. We wanted that so that we cover a broad spectrum of usage. As opposed to this kind of design are the compressors which have a very low threshold set hard within the circuit, and they would be controlled through “compression variation” only. This is equivalent to setting our compressors with the lowest threshold, and then vary compression amount with the Ratio control.

One other fact to point out is the range of a pickup signal, which is in the lower 25% of the pro signal level. This falls as well within the first quarter of the Threshold knob’s rotation range. The compression, or limiting, should only occur on peaks and for that matter, the optimum threshold point for a pickup is also in the lower setting on the Threshold knob, maybe between -30 to -20dBu (by design, this is also the reference level of the internal circuit). Around 8 or 9 o’clock, you are more than halfway within a pickup signal range. If you are to compress just peaks, you would set the threshold knob at about 9 o’clock or slightly above. At this level, a higher compression ratio makes no sense, unless is limiting you’re after. If you want to have a more audible feel of the compression, you would set the threshold knob bellow 9 o’clock, and the lower you go counterclockwise the smaller compression ratios you should use so that the pickup signal is not squashed too hard. Unless you want to use the squash as an effect! And here comes the “New York compression style” which means compress with a high ratio and low threshold, and mix the compressed wet signal with the dry signal.

Worth mentioning is that all CompIQ compressors have a hard-set signal level protection which is 1.2Vp-p or just around the pro signal level. For higher input levels than that, the circuit gets into distortion, which is generated by the protection and not within the compression electronics. Such protection is needed to avoid damages within the electronics due to input spikes or accidental DC leakage. Anyway, guitars and basses will not get to that top-level easily, unless they are put after a device that would be cranked up.

Side Chain Filter is a feature which allows a change in the side chain compression triggering frequency filter.  The purpose is to delay the start of the compressor by the low frequency with high amplitude, which otherwise would clamp the higher frequencies too early. This results in a breathable type of compression, which has a particular sound characteristic, making it feel more natural to the ear. At the same time, the sound at the output may come out” fatter” or “punchier”.

In CompIQ PRO Stella and CompIQ Twain the SCF is switchable for a pre-set amount of low-cut of the triggering frequencies. The Normal option provides a general-purpose type of compression response, while Low and Deep options add a cut of -12dB@90Hz and -12dB@200Hz on top of the Normal side chain curve, making it suitable for bass instruments.

Frequency Compensation  refers  to  the shape of the audio spectrum presented to the Side Chain Detector. Due to the nature of audio in general and musical instruments in particular, each musical note has a dominant frequency plus harmonics. The dominant frequency is always higher in amplitude than its harmonics. As musical notes fall lower in the audio spectrum (say notes on the lower strings in a guitar), their dominant frequency have biger and biger amplitudes (as opposed to notes on higher strings). That amplitude has the potential to trigger compression too early, and as a result they may over-compress the harmonics or higher notes. This is usually heard by human ear. To overcome this, we compensate the low-frequency triggering potential, by progressively delaying it towards 1KHz, as the graph below shows. This is similar to say we apply a progressive threshold, where lower frequencies see a higher threshold than higher frequencies, which see a lower threshold proper for their lower amplitude. This type of progressive compensation helps prevent the “pumping” often encountered in compressors, and makes the dynamic processing feel more natural. That is especially true for percussive instruments or for instruments rich in low frequencies, like bass.

The Normal side-chain roloff curve above is particular to all our compressors,  providing a general-purpose type of compression response. In CompIQ PRO Stella and CompIQ Twain the Side Chain Filter has two additional options: Low (-12dB@90Hz) and Deep (-12dB@200Hz) on top of the Normal curve.

The Tape Saturation analog circuit acts only on the Dry signal. This optionally-saturated signal can then be mixed with the wet, compressed signal, to infuse harmonic distortions and warm-up the audio, without affecting the dynamics of the compressed signal. The headroom of the saturation circuit is pretty high, so you need to dial in some saturation before the effect is audible. Below you can see how the filters affect the frequencies of the Dry line.

The Low & High cut filters should be used only when Tape Saturation is used, otherwise, they will affect the clean dry line, although, that might also be a desirable way of using the Dry/Wet Mix control. The filters were necessary so that they would accommodate different types of audio sources, and respond musically without introducing unwanted fuzziness on the low end (especially for bass), or make it sound brittle (especially on bright guitar pickups).

The Tilt-EQ section of the circuit is placed after the compressor, just before the Mix control, which means it acts on the wet signal only. When mixing the dry unprocessed signal, with the wet, compressed and processed signal, the effect of the Tilt-EQ is washed out little by little, as you introduce more dry signal.

The Tilt-EQ on Stella has two frequency pivot points so that it will accommodate either bass (pivot at 330Hz, which corresponds to the higher note on the highest note of a 4 or 5 strings bass), or guitar (pivot at 1KHz, which corresponds to the highest note on a 20-fret guitar). At extreme setting (CC or CCW), there is a total difference of 12dB in between lows and highs. In the middle position of the Tilt-EQ knob, the frequencies are not affected. The Tilt-EQ section can be bypassed altogether by changing the position of a jumper inside the pedal.

CompIQ series of compressors (both Stella and MINI) share the same core technology – sound wise they sound exactly the same. They have 50dB threshold range, from -40dB up to +10dB which is from average magnetic pickup level up to above line level. They both may be used on line-level FX Loops or hi-Z input on recording interfaces. Having an RMS-level detector, the compression is very accurate and the LED indication is very precise in that regard, as long as the input signal is at/around calibrated reference level. With line-level signals, which is way up, the LED’s will flash red more often, but there is nothing wrong with that. We did not provide means for re-calibrating the compression display at various signal levels because they were designed to be used mainly with instrument-level signals. CompIQ series “0dB input reference level” is hard-set at -20dBu (77.5mV). The total amount of compression depends on input signal level, usually 20dB for input signals around -20dBu (77.5mV) and around 36dB for +4dBu (1.228Vrms) input signal levels, all at inf:1 Ratio.

The re-amplification of a weak signal – as compressed signal is – is the main source for noise in compressors. Some compressors might be described as noisier than other, but the fact is they all introduce noise with amplification (the amount of noise is also dependent on amplification circuit, FET-based amplification being potentially a bit noisier; in CompIQ compressors, amplification takes place in the VCA). To correctly compare compressor’s noise, they must be set for the same exact amount of threshold, ratio and make-up gain, and be fed the same reference signal. Some manufacturers limit the Ratio of their compressors to 7:1 (Empress), or as low as 3:1 (Diamond) and those make for “very silent compressors”. Of course in this regard “silent compressor” has a subjective meaning, if it’s not a misleading statement. As far as CompIQ compressors go, keep in mind:

• at higher input signal levels, the makeup gain-related noise will be lower, because you deal with a bigger signal in the first place;
• if you set a higher threshold, hard knee, and inf:1 ratio and you affect only the peak of the signals – as this limiting setup makes sense to be used – the noise will be inaudible.
• for weak magnetic pickup signals, at the lowest set threshold and with ratios around 4:1 (which is a fair amount of compression), the CompIQ make-up gain will introduce noise similarly to studio-grade equipment.
• on top of Threshold, you have the MIX control which helps reducing noise by blending in the dry signal;
• using soft knee also contributes to reducing the need for make-up gain, so implicitly it reduces potential noise.

• Premier Guitar Magazine – CompIQ STELLA – Pedal Showcase
• Guitar Magazine – CompIQ STELLA – Review
• Premier Guitar Magazine – CompIQ MINI – Quick Hit Review
• Onlybass Forum – CompIQ STELLA – Review with sound samples (French language)
• Onlybass Forum – CompIQ MINI & STELLA – Reviews & Comments (French language)
• Talkbass Forum – CompIQ MINI – Reviews & Comments
• Talkbass Forum – CompIQ MINI ONE – Reviews & Comments
• Talkbass Forum – CompIQ STELLA – Reviews & Comments
• Basschat Forum – CompIQ STELLA – Review
• Basschat Forum – CompIQ STELLA – Reviews & Comments
• YouTube – Reviews and Demos