CompIQ STELLA
CompIQ MINI
CompIQ ONE
CompIQ TWAIN
Ziffer Overdrive
Overdrive / Switcher
Micro Booster
DITOS DI Board
The 101 of the CompIQ Line of Compressors
Side Chain Filter
The Side Chain Filter is a feature that varies the compression triggering behavior based on frequency. Its purpose is to avoid compression being triggered by high-amplitude low-frequency content, which can prematurely squash higher frequencies and result in a muffled sound with fewer highs. To address this issue, we have implemented a downward filtering of the side-chain from 1kHz, as depicted in the accompanying graph. By filtering out the lows in the side-chain, compression is no longer triggered for those specific frequencies in the VCA that the program sound is passed through. As a result, the lows are louder and less compressed at the output of the compressor, which produces a distinctive sound characteristic perceived as fuller, more natural, or punchier.
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.
Side Chain Frequency Compensation
Frequency compensation refers to the process of adjusting the audio spectrum presented to the Side Chain Detector. In music, each note has a dominant frequency and harmonics, with the dominant frequency being higher in amplitude than its harmonics. As notes move lower in the audio spectrum, such as those played on the lower strings of a guitar, their dominant frequency becomes more prominent in amplitude, which can trigger compression too early and over-compress the harmonics or higher notes. This effect is perceptible to the human ear. To address this issue, we apply progressive filtering to the low-frequency triggering potential, starting at 20KHz and gradually filtering downwards using additional high-pass filters at 1KHz. This progressive compensation helps to prevent the “pumping” often encountered in compressors and results in a more natural and dynamic processing, which is especially noticeable in percussive instruments or those rich in low frequencies, such as bass.
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.
Crossover
The CompIQ Twain boasts a first-order Linkwitz-Riley crossover with a variable range of 70Hz to 1KHz, dividing the input signal into two distinct frequency bands processed by the dual compression engines. Additionally, the crossover output feeds the Dry Line, enabling seamless mixing of Dry and Wet signals without any phase cancellations, regardless of the crossover’s position.
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.
CompIQ Twain Crossover Frequencies & Best Saturation Range
Tape Saturation Lo & Hi-Cut filters
The CompIQ Stella and CompIQ Twain compressors both offer an analog Tape Saturation circuit that exclusively affects the Dry signal. This allows the user to add optional saturation to the signal, which can then be blended with the compressed Wet signal to imbue harmonic distortion and warm up the audio, all while maintaining the dynamics of the compressed signal. However, it’s important to note that the saturation circuit has a high headroom, meaning some saturation must be dialed in before the effect becomes audible.
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.
