70Hz to 1KHz
< 110mAh @ 18VDC
with optional DITOS DI board
Manual: 0.12 ms/dB to 12 ms/dB
Manual: 1.2 ms/dB to 120 ms/dB
< 63mAh @ 18VDC
< 38mAh @ 12VDC
< 23mAh @ 12VDC
Initially developed by David Blackmer, founder of dbx Inc., the original dbx 202 “Black Can” Voltage Controlled Amplifiers (VCAs) continue to be employed in operating consoles to this day. These pioneering VCAs, which were the first of their kind to be suitable for professional audio equipment, were constructed with a gain cell comprising eight discrete transistors. Subsequent advancements in integrated circuit technology have since overcome the limitations of earlier designs, resulting in significantly improved performance.
The CompIQ series of compressors, for instance, utilize THAT Corporation’s Blackmer® VCAs, which are distinguished by their exponential control characteristic (where gain varies directly in decibels), exceptionally wide dynamic range, and low signal distortion. These VCAs are notably neutral in their tonal character, and therefore, impart minimal or no coloration to audio signals.
The precise envelope decoded by this detector is subsequently employed to trigger the Voltage Controlled Amplifier (VCA) in accordance with user-defined parameters such as Ratio, Knee, SCF, Threshold, Attack, Release, and Gain.
The Threshold control on the CompIQ line of compressors is designed to accommodate a wide range of input signals, ranging from very weak to pro-audio level signals. The top end of this range corresponds to the +4dB pro signal line level, located at the far clockwise end of the Threshold knob. This generous headroom helps to prevent distortion caused by high-level spikes, which was a deliberate design choice. Some compressors are prone to distortion due to insufficient headroom, but this is not the case with the CompIQ line of compressors.
This product line is designed to accommodate both lower and hotter signals, making it suitable for use with synths and other line-level devices. This design choice was made to ensure that the compressors can be used for a broad range of applications. In contrast, some compressors have a very low threshold set hard within the circuit and are controlled solely through “compression variation”. This is equivalent to setting the CompIQ compressors to their lowest threshold and varying the compression amount using the Ratio control.
It is worth noting that the range of a pickup signal typically falls within the lower 25% of the pro signal level, which is also covered by the first quarter of the Threshold knob’s rotation range. Compression or limiting should only occur on peaks, and the optimal threshold point for a pickup signal is generally between -30 to -20dBu.
When compressing peaks, the Threshold knob should be set at around 9 o’clock or slightly above to achieve the desired effect. Higher compression ratios are not necessary at this level, unless limiting is the goal. If a more pronounced compression effect is desired, the threshold should be set below 9 o’clock. As the threshold is lowered, smaller compression ratios should be used to avoid excessive squashing of the pickup signal, unless this effect is intentionally desired. This is similar to the “New York compression style”, which involves compressing a signal with a high ratio and low threshold, and then blending the compressed signal with the unprocessed signal to achieve a balanced dynamic range.
The utilization of the SCF (Side Chain Filter) provides the capacity to mitigate the undesirable pumping artifacts that frequently occur when applying a “high ratio / low threshold” compression technique. The resulting compression sensation from the SCF is distinct from other methods of removing pumping, such as raising the threshold, lowering the ratio, utilizing soft-knee compression, or blending dry over wet signals, or a combination of these techniques. Incorporating the SCF with other controls allows for greater flexibility in how the compression is employed on various audio content.
The standard side-chain roll-off curve utilized in all of our compressors is designed to deliver a compression response that aligns with the human ear’s perception of sound, making it a versatile option. It’s worth noting that this roll-off curve is also progressive, with a reduction of -12dB at 2KHz compared to 20KHz.
CompIQ Stella and CompIQ Twain compressors offer two additional options for the Side Chain Filter: Low (-12dB per octave at 90Hz) and Deep (-12dB per octave at 200Hz) in addition to the Normal curve, which provides a general-purpose compression response based on human auditory perception. The newly introduced variable SCF option on the CompIQ Mini can be adjusted by turning the knob fully clockwise to free up -12dB per octave at 90Hz. This feature caters well to guitar and bass instruments, as well as other instruments generating high amplitude low-frequency waveforms. When the SCF knob is set at noon, the side-chain detector is presented with a flat copy of the input signal, referred to as Normal processing. However, when the knob is fully counterclockwise, the SCF boosts low frequencies below 90Hz with up to +12dB per octave, making the compressor more sensitive to signals generated by some instruments like single coil guitars.
To provide visual representation, we have included a chart demonstrating the matched levels of both the internal and external circuits with the crossover set to 1KHz, the output set to buffer level, and Mix adjusted to 100% Wet. It is evident from the chart that the phase of each signal component aligns almost perfectly across the audio spectrum.
It is worth noting that the input signal’s phase is a straight line, while the output signal’s phase progressively twists from lows to highs, ranging from almost 0° on the extreme lows up to 400° on the extreme highs. This phenomenon is normal and is the result of the signal being separated by the crossover’s band filters and then recombined at the output after passing through the compression engines. Therefore, when switching from Bypass to Effect, there may be a perceived delay in frequency despite no audible loss of frequency throughout the audio spectrum.
The following drawing illustrates the Crossover Knob Frequency Scale and the most suitable setting for utilizing the Saturation feature.
For the CompIQ Stella, the LPF and HPF can be activated by removing the corresponding internal jumpers. Meanwhile, the CompIQ Twain provides variable filters that can be accessed via small trim knobs. The HPF is available for the Lows band, while the LPF is available for the High band. In both compressors, the HPF is situated before the Saturation engine, while the LPF comes after.
The effect of the filters on the frequencies of the Dry line can be observed in the illustration below.The implementation of the Low and High cut filters is recommended only in conjunction with the Tape Saturation feature. Otherwise, the filters may have an effect on the clean, dry signal, although this may be an intentional use of the Dry/Wet Mix control. The filters were introduced to provide flexibility for processing various audio sources while maintaining musicality, without introducing undesirable artifacts such as muddiness on the low end (particularly with bass) or harshness on bright guitar pickups.
The Stella’s X-EQ is equipped with two frequency pivot points suitable for accommodating either bass (330Hz pivot point, corresponding to the highest note on a 4 or 5 string bass) or guitar (1KHz pivot point, corresponding to the highest note on a 20-fret guitar). In extreme X-EQ knob settings (fully clockwise or fully counterclockwise), there is a total 12dB difference between low and high frequencies. In the central position of the X-EQ knob, no frequency alterations occur. The X-EQ section can be bypassed entirely by adjusting a jumper’s position within the pedal.
Compressors typically experience an increase in noise due to the amplification of make-up gain. As compression increases, more make-up gain is required, which adds amplification noise to the signal. This noise is then amplified by any subsequent pedals or amplifiers in the signal chain. Additionally, any amplification device preceding the compressor may introduce noise, which is subsequently amplified by the make-up gain circuit.
It is crucial to recognize that if a compression setting necessitates a significant amount of make-up gain, the amplification noise will be substantially higher and noticeable during periods of signal absence. The signal-to-noise ratio is particularly low during pauses, where the noise level may surpasse that of the signal, resulting in negative SNR. It is unrealistic to anticipate an absence of noise when adjusting the gain by +20dB. However, compressing the signal at -20dB and then restoring it with a gain of +20dB will result in barely perceptible amplification noise, albeit still evident. If the maximum make-up gain is required, the compressor is in hard-limiting territory and it should be applied only to peaks and not to the entire signal.
To accurately compare compressors for noise, it is imperative that they are configured with the same threshold, ratio, and make-up gain, and fed the same reference signal. Some manufacturers restrict the ratio of their compressors to as low as 3:1 or 7:1, resulting in “very quiet compressors” since they do not require as much re-amplification. It is important to note that the term “quiet” is subjective and may be misleading.
In particular, with the CompIQ Twain, the Stacked Mode can generate unnecessary noise if not set up correctly. The Twain Settings Examples explain how to control amplification noise in this mode, primarily by adjusting the compression and make-up gain in the second (highs) engine more than in the first (lows) engine. You can also pass some of the frequencies to compress to the second engine by raising the lows threshold, using the Low or Deep side-chain filter, and using the soft knee to mitigate noise or compression feel. These controls can be combined in both engines to find the optimal setting for your specific application.
Dual-band processing is generally more challenging and requires a specialized type of compression. It is essential to understand that what works for full-band compression cannot be directly applied to dual-band compression. Furthermore, the crossover used in dual-band compression is always-on and composed of numerous passive components that inherently generate thermal noise. This noise is also amplified with the make-up gain, a phenomenon that applies to all dual-band compressors.
An effective strategy is to comprehend how the compression controls such as threshold, ratio, knee, timing, blend, side-chain filter, and gain impact compression in general and identify the desired outcome. You can combine these parameters to configure compression in a manner that reduces the need for high make-up gain.
It is important to note that the level of noise generated by the makeup gain is typically lower when dealing with higher input signal levels, as the signal itself is larger. Additionally, when employing a limiting setup with a higher threshold, hard knee, and inf:1 ratio that solely affects the peak of the signal, any resulting noise will be inaudible.
When working with weak magnetic pickup signals, employing a ratio of around 4:1 and a low threshold on the CompIQ can generate a fair amount of compression, while still maintaining a noise level similar to that of studio-grade equipment. To further minimize noise, the MIX control can be utilized to blend in dry signal, while a soft knee can help to reduce the need for makeup gain, thereby reducing potential noise.
Power sources can be a significant source of noise when operating electronics. It has been observed that switching power supplies generally introduce hissing sound to the system. To mitigate this, we strongly recommend the use of well-filtered and regulated power sources of good quality. It should be noted that most pedals are not designed to accommodate large capacitors and other necessary electronics required for effective power conditioning. As such, they are not intended to function as power source filters.
The CompIQ line offers a gain reduction meter for all of its compressors, which indicates the amount of compression applied to the input signal in dB. However, the metering ladder varies depending on the product and has a limited number of LEDs. As a result, compression may be “invisible” between LEDs. For optimal metering, a minimum of 20 LEDs is recommended.
Each product’s metering is designed and calibrated to reference comparators to 9-12VDC, providing an accurate indication of gain reduction. However, the CompIQ Twain can also operate at 18VDC. When powered at 18VDC, some calibrated thresholds for metering may shift, resulting in a metering indication of around -3dB less. Although proper powering of an electronic circuit is with a fixed voltage +- some tolerance, 80-100% voltage up shifting shifts some calibrations within the blocks of circuits inside. While the audible side of the change may be favorable, the metering’s precision is affected and introduces variation.
In some circumstances outside of normal usage, such as when powering the pedal at a higher voltage and switching the knee, the meter LEDs may remain “locked” lit. This is due to an electric spike introduced by switching the knee, which triggers the LEDs briefly, even if no input signal is present. To prevent this, it is recommended to switch the knee when there is no input signal but with the input and output plugs inserted in the pedal.
To switch off the remaining lit LEDs, the pedal must be powered off and on again or played with a signal higher than the remaining lit LEDs, which resets the comparators. Alternatively, the pedal can be powered with 9-12VDC instead of 18VDC.
The CompIQ line of pedals can operate within a power range of 9-18VDC. However, to ensure optimal performance and protect the circuits from power supply failure, we have conservatively designed and calibrated certain portions of the circuits, such as the gain reduction meter, to run in the 9-12VDC range. It is imperative to use high-quality, regulated power sources as exceeding the 18VDC maximum could cause active components to fail.
To prevent voltage spikes when connecting the pedals to the power supply, it is recommended to pre-connect the pedals before powering on the power supply. It is also advisable to power the entire pedalboard at once by switching on the AC switch on the power supply or plugging it into the AC wall wart, as this helps to control the current draw and regulate the voltages at each available power output.
Although the circuits in our pedals include reverse polarity protection, there are limits to what these protections can handle. Therefore, it is essential to use caution and only use power supplies that fall within the recommended voltage range to ensure optimal performance and protect the longevity of the circuits.
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