The 101 of the CompIQ Line of Compressors

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, -20dBu 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 the limiting that you’re after. If you want to have a more audible feel of the compression, you would set the threshold knob below 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 to balance the overall dynamics of the signal.

On CompIQ Stella, CompIQ Mini, and CompIQ Twain the side-chain high-pass filter is switchable for a pre-set amount of cut of the targeted low 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 (-12dB@130Hz for the CompIQ Mini) on top of the Normal side chain curve, making it more suitable for bass-rich or percussive high amplitude input signals.

The SCF processing allows for removing the pumping usually associated with the usage of the “high ratio / low threshold” type of compression. The SCF provides a slightly different compression “feel” when compared with other methods of pumping removals such as raising the threshold, lowering the ratio, using soft-knee compression, blending dry over wet signal, or a combination of all or any of these controls. Of course, the SCF can be combined with all the other controls, giving even greater flexibility in the way the compression is applied to different audio content.

The Normal side-chain roll-off curve above is particular to all our compressors. It provides a general-purpose type of compression response that corresponds to how the human ear perceives the sound. You may notice that even the Normal side-chain roll-off curve is progressive, and is -12dB lower at 2KHz than it is at 20KHz.

On CompIQ Stella and CompIQ Twain, the Side Chain Filter has two additional options: Low (-12dB per octave at 90Hz) and Deep (-12dB per octave at 200Hz) on top of the Normal curve. The Deep SCF option on the CompIQ Mini is set to free up -12dB per octave at 130Hz which should serve well both guitar and bass instruments, as well as many others.

When the SCF’s switchable options are combined with Knee selection, variable Ratio, and Threshold settings, and the Dry/Wet Mix, they can all fully compensate for the option of a variable side-chain filter control, which would have been difficult to fit into our small enclosures.

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

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

Dry Line No Filters

Dry Line Lo Filter

Dry Line Lo & Hi Filters

Dry Line Hi Filter

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 making it sound brittle (especially on bright guitar pickups).

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 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.

It is important to note that if your compression setting needs a lot of make-up gain then the amplification noise will be way higher and audible during the absence of the working signal (music pause). This is because the signal to noise ratio is very low during such pauses (actually, the noise is higher than zero signal, which means you are in negative SNR) when compared with the signal to noise ratio during compression. You should not expect to dial in +20dB of gain and hear no noise. However, if you compress the signal -20dB then recover it with +20dB of gain then the amplification noise is only hardly audible, yet obviously there. You cannot avoid this. And, if you want to understand how hugely loud 20dB of gain gets, set the compression to 1:1, dial in the make-up gain to the maximum and play. In fact, if you need the entire available make-up gain you are in hard-limiting territory and no longer compressing.

To correctly compare compressors 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” because they don’t need as much re-amplification. Of course in this regard, the “silence” characteristic has a subjective meaning if it’s not a misleading statement.

Particularly with the CompIQ Twain, it is easy to add more noise than necessary in the Stacked Mode, which puts the compression engines in series, like you would stack two pedals. We do explain more about this in the Twain Settings Examples, and the trick to controlling amplification noise in this mode is to use the last (highs) engine compression and make-up gain more than what you use in the first (lows) engine. You would try not to compress too much in the first engine and keep the make-up gain low, then go furthermore in the second engine and use its make-up gain as a master gain. Another trick is to pass some of the frequencies to compress to the second engine by means of, raising the lows threshold, using the Low or Deep side-chain filter, and using the soft knee to mitigate either noise or compression feel. You may combine these controls in both engines to find the sweet spot for your application.

The dual-band processing is usually more tricky and is more of a specialty type of compression, where it is easier to set it “wrong”, although there is no wrong in setting it in any way. It is just that what works for full-band compression cannot be applied one-to-one to dual-band compression.

Besides that, the crossover used in dual-band compression is an “always-on” circuit that has many passive components which are needed in the filters section, and all the resistors that compose these circuits inherently add what is called “thermal noise”. And that, of course, is also getting amplified with the make-up gain. This is valid for any dual-band compressor.

Here is a working strategy. Try to understand how the compression controls (threshold, ratio, knee, timing, blend, side chain filter, gain) affect compression in general and ask yourself what you are trying to achieve. Combine these parameters to set up compression in such a way that the make-up gain can be set lower.

Worth knowing:

• 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 reduce noise by blending in the dry signal;
• using a soft knee also contributes to reducing the need for make-up gain, so implicitly it reduces potential noise.

Power sources are also a proven source of adding noise to electronics. Switching power supplies will almost always add hiss. We recommend using only good quality, well filtered, and regulated power sources. The pedals in general do not have enough space to fit large capacitors and additional necessary electronics for good power conditioning. And, pedals are not supposed to filter power sources anyway.

• Knee
• Timing
• Side Chain Filter
• EQ Pivot
• Dual-Band/Stacked
• Power On/Off

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 the input cable’s jack is not inserted in the pedal.

The gain reduction meter needs an input signal that varies up and down the thresholds set for each LED, and while a raising signal lits them, they must also be turned 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.

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 fails and supply higher 20^ish Volts into the pedal, then those active components might fail.

It is advisable to have the pedals pre-connected to the power supply prior to powering the power supply from the AC outlet. In other words, only power the pedalboard at once by switching ON the AC switch on the power supply, or put the plug into the AC wall wart if no AC power switch is available. This prevents the possibility of a short burst of voltage when a load is connected to a powered DC port. If you power the entire pedalboard at once on the AC side (power switch or wall wart plugging) then the distributed load on the DC side of the supply is already connected and the draw of current might be better controlled and voltages better kept on regulation at each available power output.

The circuits in our pedals have other protections as well, like reverse polarity, yet there is a limit that these protections can handle.

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