The 101 of the CompIQ Line of Compressors

MINI Pro vs. Other Minions

Wanna know more about mini compressor pedals? We compiled a Technical Shootout for most performance and popular mini compressor pedals available. Click here to find out how CompIQ MINI Pro stands out.

 

The Blackmer^® VCA

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.

 

The RMS-Level Sensor

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 the 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 Range

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. Actually, we did that with the CompIQ MINI ONE Compressor – which is more suitable for simple operation.

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 circuits have a hard-set signal level protection; which is around 1.2Vp-p or just around… pro signal level. For higher input levels than that, the circuit gets into distortion, which is generated by the protection section of the circuit and not within the active electronics, like buffers and VCA. 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.

 

The Side Chain Filter

Side Chain Filter is a feature that 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, 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.

 

Tape Saturation Lo & Hi-Cut filters

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.

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).

Below you can see how the filters affect the frequencies of the Dry line.

 

X-EQ

The X-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 X-EQ is washed out little by little, as you introduce more dry signal.

The X-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). In extreme settings (CC or CCW), there is a total difference of 12dB in between lows and highs. In the middle position of the X-EQ knob, the frequencies are not affected. The X-EQ section can be bypassed altogether by changing the position of a jumper inside the pedal.

 

Line-level Signals

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.

 

Compressor Noise

The re-amplification of a weak signal – as the 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.

 

Independent Demos, Reviews & Comments

• Guitar Magazine – Review: Becos CompIQ STELLA Pro Compressor
• Premier Guitar Magazine – Quick Hit Review: CompIQ MINI
• 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 – Reviews & Comments
• YouTube – Reviews and Demos

Note: This document will be constantly updated with new information.

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Disclaimer

^{On Monday, June 22, 2020, we have been contacted by a representative of PMI Media Group and being informed that the word TILT™ is a USA Registered Trademark owned by AMH Sales, Inc. DBA PMI Audio Group Corp. in Class IC 009 registration #3971079. Currently, we are complying in good faith with the notification of the trademark owner and we renamed the equalization control on the Stella compressor as X-EQ. More details here.}