Description
Studio-level audio performance in a pedal format
The CompIQ STELLA Pro Compressor is an all-analog externally powered or battery-operated compressor pedal designed for guitar and bass and hand-built around the top-class 4320 THAT Analog Engine®. The amount of control it offers is staggering and probably never before seen in a compression pedal, especially of this size. We didn’t leave out anything that helps to bring out a truly clean, accurate, and transparent compression. At the heart of processing, a true RMS-level detector measures the input signal and applies accurate feed-forward compression through a transparent sounding, high-performance Blackmer® VCA.
Full control over compression parameters
With so many controls, one may wonder how can this be tamed and furthermore, properly used in a live setup. Don’t let yourself overwhelmed. We provided sufficient options not only for in-depth control but also for making things easier. For instance, with the flip of a switch, you can take out the Manual Attack & Release controls (the most daunting of the art of compression) and let the Dynamic Auto Timing analog circuit do the right thing for you. Two choices are available, Fast or Slower timings, and both respond gracefully to any playing style. In both settings, transients are handled faster while steady signals benefit from longer release timings. Faster timings present a more accentuated compression feel and are well suited for limiting purpose.
However, using the manual control of Attack and Release timings will expand the compression flavors by an order of magnitude. To mention just a simple trick: delay the attack time a little while bringing back a faster release time and you will end up with a punchy and proper sound for country chicken pickin’ or for instrumental stand-out soloing. Combine this with the Side Chain Filter and the X-EQ and increase your options even further. All these together will also remind you of an optical-soul type of compression, demonstrating the tremendous versatility of this pedal.
The full-scale Ratio (1:1 to infinite:1), the instrument to line-level Threshold (-40dB to +10dB) range, and up to +20dB of Makeup Gain, all in continuous controls, add to the plethora of switchable options to further attain the ideal compression for any musical program.
A Dry/Wet Mix allows for parallel compression (a.k.a. the New York style), where the desired amount of unprocessed input signal is mixed with the compressed signal, for a more natural effect application.
Compression subtleties
Additional features are available for the very demanding players. The Side Chain Filter has three selectable options – Normal, Low and Deep -, very helpful for bass instruments or when a fuller output is needed. To keep things simple, set the filter to Normal and the compressor will just act naturally in most instances. The Normal side-chain processing presents a non-linear, high-pass characteristic above 1KHz, which balances the potential trigger-difference between the energy of low and high frequency. Such a feature is usually available only in high-end studio compressors, and it is intended for a natural effect application even on higher compression ratios. If lower-frequency notes trigger compression yet too fast, then the Low (-12dB@90Hz) or Deep (-12dB@200Hz) high-pass filters will slightly delay the compression, freeing up the low-end just enough for the spectrum to breath out and prevent the early or over-compression of highs.
The Compression Knee can be selected between Hard and Soft, each option having its own sonic signature. Hard Knee compression acts fast and squishes hard. Use this if you aim for limiting or in-your-face compression effect. Soft Knee compression acts progressive and gentle, helping to create a transparent effect application, even at the highest ratio.
The X-EQ equalization circuit dawned in the 70′ Hi-Fi era, has two selectable options for its pivot frequency: High (at 1KHz) proper for guitar and Low (at 330Hz) suitable for bass. This is a post-compression applied correction that can be either necessary for voice compensation from one instrument to another, or desired, for your particular sonic signature.
Harmonic coloring
On top of all these, we added an analog Saturation circuit which can add harmonic distortions to the dry line (only), which can then be mixed with the compressed wet line, for precise balancing of the effect. This circuit rivals the vintage studio tape-overload compression effect which was a studio recording trick during the ’60s. Tape saturation is a pleasing sort of distortion arising when high amplitude audio signals are recorded on magnetic tape.
The Saturation control can vary in intensity from nothing to mild and up to warm but powerful overdrive. The result is either subtle, adding richness to the sound peaks, or obvious, with a tube-like screaming distortion feel when all audio spectrum is saturated. If needed, Low and High-frequency cut filters can be engaged by removing two internal jumpers. This helps eliminate oversaturated low-frequency fuzziness or prevent high-frequency from sounding too pointy. The auxiliary Level control on the dry line will compensate for the volume loss introduced by a higher saturation setting. This parallel processing is delicately brought together and leveled up with the Mix blend knob, similarly with using a dedicated studio summing amplifier. The parallel tape saturation feature also transforms CompIQ Stella into a compressor/overdrive effect.
An 8-LED compression display indicates the amount of effect applied to the input signal (or gain reduction), providing visual feedback over how much the sound is processed.
Pristine audio processing
The CompIQ series of compressors is not gonna alter the magic voice of your instrument. They preserve the original guitar or bass tone while providing unobstructed, pristine audio compression. The high dynamic range of these compressors allows for natural-sounding clean tones and low noise, artifact-free audio processing without the distortions usually introduced by optical compressors.
Hear the sound on bass
Sound samples courtesy of Test de matériel from France. Alternating compressor Off and On, with or without Tape Saturation. Scroll below for video demos.
Key features
- True analog bypass
- Blackmer® VCA analog compressor
- True RMS-level detector
- Ratio 1:1 – inf:1 (limiter)
- Threshold -40dB to +10dB
- Make-up Gain -6dB to +20dB
- X-EQ with selectable frequency pivot 330Hz/1KHz
- EQ bypass – jumper selectable
- Manual Attack 0.12 – 12 ms/dB
- Manual Release 1.2 – 120 ms/dB
- Soft/Hard compression knee
- Manual timings or Fast/Slower dynamic auto attack and release timings
- Normal/Low/Deep side-chain filter
- Dry/Wet mix
- Tape Saturation on the dry line with Level compensation and Low/High-frequency cut filters (jumper selectable)
- 8-LED compression display
- Socketed hi-quality FET audio IC, low tolerance parts and WIMA or KEMET audio capacitors
- Genuine Hammond black-powdered aluminum enclosure
- Runs on standard 9V internal battery or 9-12 V DC external power supply, center negative, 12mm long barrel plug (not included)
- 3-year warranty
More info
Manual
Video demo | More
Compare compressors
COMPIQ 101
The CompIQ series of compressors
Side-Chain Frequency Compensation
Compressor / Limiter
Dual Band / Stacking
2
Blackmer® VCA
True RMS-Level Sensor
Normal / Low / Deep
lows only
YES
-9dB to +6dB
> +6dBu signal levels
Linkwitz–Riley
70Hz to 1KHz
1:1 to inf:1
both bands
-40dBu to +10dBu
both bands
Auto Fast / Slower
both bands
F / S: 5‐7ms / 10-15ms
F / S: 70ms / 100‐220ms
-6dB to +20dB
both bands
Hard / Soft
both bands
Through Make-up Gains on Wet line (boost/cut)
-
YES
On Dry Line
adjustable
Lo / Hi Cut filters and Level controls
6-LED
both bands
-
9-18VDC center negative
Ø 5.1/2.1mm, 12mm long
< 69mA
Compressor / Limiter
Single Channel
1
Blackmer® VCA
True RMS-Level Sensor
Normal / Low / Deep
YES
-
-
-
1:1 to inf:1
-40dBu to +10dBu
Auto Fast / Slower
F / S: 5‐7ms / 10-15ms
Manual: 0.12 ms/dB to 12 ms/dB
F / S: 70ms / 100‐220ms
Manual: 1.2 ms/dB to 120 ms/dB
-6dB to +20dB
Hard / Soft
X-EQ +/-6dB with Low / Deep frequency pivots
YES
YES
On Dry Line
adjustable
Lo / Hi cut filters
(inside jumpers)
8-LED
YES
9-12VDC center negative
Ø 5.1/2.1mm, 12mm long
< 29mA
Compressor / Limiter
Single Channel
1
Blackmer® VCA
True RMS-Level Sensor
Normal / Deep
YES
-
-
-
1:1 to inf:1
-40dbu to +10dBu
Auto Fast / Slower
F / S: 5‐7ms / 10-15ms
F / S: 70ms / 100‐220ms
-6dB to +20dB
Hard / Soft
-
-
YES
-
-
5-LED
-
9-12VDC center negative
Ø 5.1/2.1mm, 12mm long
< 25mA
Compressor
Single Channel
1
Blackmer® VCA
True RMS-Level Sensor
Normal
YES
-
-
-
1:1 to inf:1
Lo: -40dBu fixed; Hi: -40dBu to +10dBu inside trimmer
Auto Slow
10-15ms
100‐220ms
-6dB to +20dB
Hard
-
-
YES
-
-
5-LED
-
9-12VDC center negative
Ø 5.1/2.1mm, 12mm long
< 25mA
MINI Pro vs. other minions
Do you want to 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.
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.
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 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).
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.
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
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 Stella, CompIQ Mini, 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 which is frequency-compensated to resemble the human ear perception of sound, while Low and Deep options add a cut of -12dB@90Hz and -12dB@200Hz (-12dB@130Hz for the CompIQ Mini) on top of the Normal side chain curve, making it suitable for bass instruments.
Side Chain Frequency Compensation
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 bigger and bigger 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 the human ear. To overcome this, we compensate for 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 rolloff curve above is particular to all our compressors, providing a general-purpose type of compression response that corresponds to how the human ear perceives the sound. In CompIQ 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 Deep SCF is set to -12dB@130Hz for the CompIQ Mini.
Crossover
The
CompIQ Twain features a variable 70Hz to 1KHz Linkwitz–Riley type of crossover which splits the input signal into two frequency bands which are processed independently by the two compression engines. The output of the crossover also feeds the Dry Line, so mixing the Dry and Wet signals is possible without phase cancellations, regardless of the crossover’s set point.
Below is a plot showing matched external and internal circuit levels with the crossover set at 1KHz, the output set at the buffer level, and Mix set to 100% Wet. As you can see, the phase of each signal component is almost perfectly aligned in the audio spectrum.
It is worth noting that while the input signal’s phase (dotted green) is a straight line, the output signal’s phase (dotted red) is progressively twisted from lows to highs (from almost 0° on the extreme lows up to 400° on the extreme highs). This is normal and is the result of the signal being separated by the crossover’s band filters, and then being re-combined at the output, after passing the compression engines. As a result, when switching from Bypass to Effect, the ear perceives the frequency delays although there is no audible loss of frequency throughout the audio spectrum.
Bellow is a drawing showing the Crossover Knob Frequency Scale and the most appropriate setting for using the Saturation feature.
CompIQ Twain Crossover Frequencies & Best Saturation Range
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. 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).
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 compressed signal is – is the main source for noise in compressors. Some compressors might be described as noisier than others, 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 or as low as 3:1 and those indeed make for “very silent compressors”. Of course in this regard the “silence” characteristic has a subjective meaning, if it’s not a misleading statement. As far as CompIQ compressors go, these are the facts:
- 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.
Switching noise
Pops or static noise may occur when switching the following settings with the pedal engaged:
- Knee
- Timing
- Side Chain Filter
- EQ Pivot
- Dual-Band/Stacked
- Power On/Off
Gain Reduction Meter
The gain reduction meter is available for all compressors in the CompIQ line. They measure how much compression is applied to the input signal. The indication is in dB. Depending on the product, the metering ladder is differently configured. Keep in mind that due to the limited number of LEDs in the meter, the compression is “invisible” in between the LEDs. Ideally, a full meter scale would have a minimum of 20 LEDs, one for each dB of reduction.
The metering in each product was designed and calibrated to reference the comparators to 9-12VDC for an accurate gain reduction indication. However, the CompIQ Twain can also be powered at 18VDC. At 18VDC, several thresholds that are calibrated for metering are a bit shifted, and as a result, the metering shows around -3dB less in the meter. Usually, a proper powering of an electronic circuit is with a fixed voltage +\- some tolerance. But 80-100% voltage up shifting, also shifts some calibrations within the blocks of circuits inside. While the audible side of the change is for the better and likable, the precision of the metering reacts to this shifting and introduces a variation.
There is a possibility that the meter LEDs remain “locked” lit in some conditions outside the normal usage of the pedal. For example, this may happen when powering the pedal at a higher voltage and switching the Knee in some particular circumstances such as when the knobs are set for compression but no input signal is present or input cable’s jack is not inserted in the pedal.
The gain reduction meter needs an input signal that goes up and down against the thresholds on each LED in the meter and while they are lit by a raising signal, they must also be switched off by a decaying signal. The electric spike introduced by switching the knee (which is a change of the operation mode of a portion of a circuit while also setting the rest of the controls for compression) varies very shortly and it does trigger the LEDs although no signal on the input of the metering circuit is present so that the LED’s are reset. Nothing is broken and nothing breaks – is just a condition you put the circuits in, but that condition is different from the intended usage of the pedal.
To prevent that, switch the knee when you don’t play but you must have the input and output plugs inserted in the pedal. To switch off the LEDs that remain lit, power off the pedal and then on again OR, play your instrument with a signal higher than the LEDs on the display that remain lit. This way the circuit sees the decaying signal and the comparators are reset. Alternately, power the pedal with 9-12VDC instead of 18VDC.
Powering voltage range for the CompIQ line of compressors
Although all CompIQ line of pedals can be powered in the 9-18VDC range, we conservatively designed and calibrated some portion of the circuits (like the gain reduction meter) to be run in the 9-12VDC range. The headroom is more than enough at these voltages, and we can also protect the circuits in the long run from accidental failures of power supplies.
Please be sure you only use good quality and regulated power supplies because the 18VDC is the absolute maximum for some of the ICs inside. And although they might still support some minor voltage spikes, say at up to 10% you might still be safe, if the power supply spikes more or fails altogether and bursts a constant 20ish Volts into the pedal, then those active components might fail.
The circuits have other protections as well, like reverse polarity, yet there is a limit these protections can handle. That is valid for all our compressors.
Demos, reviews & comments
Blog post: The 101 of the CompIQ line of compressors
CompIQ TWAIN
CompIQ STELLA
CompIQ MINI
CompIQ ONE
OD / MIDI Switcher
In short, it’s what I’ve always wanted of a compressor pedal. The Stella can sound wonderfully transparent, or full of character, and there’s oodles of control at your fingertips. Bass players should absolutely love this thing (though I suspect they may be even more enamored with the company’s new split-band compressor).
The CompIQ Stella has a ridiculous amount of power for a small stompbox. Better still, it's a transparent compression that only colors the tone as much as you allow it, unlike many lower-end boxes that simply squash tone and volume. That's the sign of a good unit - delivering compression power, clarity, and flexibility to control exactly what you want to hear from a guitar.
This pedal is designed to provide an array of features – with rack unit-levels of tweakability – in a pedalboard-friendly format. A highlight of the CompIQ Pro Stella Compressor is its analog tape saturation circuit.
CompIQ PRO Stella for guitar and bass delivers dizzying array of features. There are a staggering number of parameters onboard, which promise the versatility of a rack unit in a compact stompbox.
This is a highly versatile and pedal board friendly compressor. I'm not aware of anything on the market that packs this much punch in terms of functionality. In many ways, it has raised the bar for compressor pedals. The words "Pro Compressor" on the face of the compressor is appropriate. There is a whole lot of versatility in an amazingly small package.
Knob-heavy pedal offers compression, limiting, tape saturation and more.
