Uhbik-Q: Semi-Parametric Equalizer
You will find semi-parametric equalizers (EQ) in any professional studio. Apart from volume control and summing, equalization is the most common type of signal processing...
So it is hardly surprising that EQ is a highly controversial topic in the audio world! For some, the most important factor is the sheer number of frequency bands, for others it is the ease of use. Equalizer characteristics are often described in highly subjective terms such as ‘transparency’ and ‘warmth’. Heated debates are commonplace – to quote a literary friend, “the altercation is so bitter because so little is at stake!”
Certain EQ properties CAN be judged objectively. For instance, many digital EQs suffer from overly steep HF filters, which either leads to irritating artifacts or a lack of high end. Same at the bass end of the spectrum, where certain algorithms require adequate mathematical precision.
Also, the compulsion to minimize CPU usage at all costs often tempts developers to cut too many corners and accept lower-quality results, which is especially bad news for an EQ.
How many knobs do we need? Some EQs offer control over so many parameters that operating it becomes a science unto itself, with diminishing returns per knob. Other designs take it to the opposite extreme and don’t offer enough control for the job at hand.
The Uhbik-Q design goes for maximum flexibility from a minimum of controls, and lowest possible CPU-usage without compromising audio quality. It combines freely tunable frequency bands with presets for other options, and Q-factors automatically adjust to suit the current gain.
Frequency and Gain
Uhbik-Q has two semi-parametric equalizer bands. This means that the Q- factors, unlike in fully parametric EQs, are not user-definable (they are cleverly taken care of). The two tunable bands offer a selection of useful modes - low / high shelves as well as bell curves with various Q-factors.
The frequency knobs are tunable from low mids to beyond the upper limit of human hearing (>20 kHz). The gain knobs determine how much the signal is attenuated or boosted. Despite the rather wide range of +/- 24 dB, fine adjustments are easy: simply click and drag the label below the knob instead of the knob itself.
Band 1 and Band 2 modes
The switches between the frequency and gain knobs select filter characteristic for each band:
off: the filter is deactivated, it does not affect the sound.
lowshelf: classic low-shelf filter. The gain knob controls the amplitude of frequencies below the value set by the frequency knob.
wide bell: the gain knob controls the amplitude of frequencies around the value set by the frequency knob. Very low Q-factor!
flex bell: the gain knob controls the amplitude of frequencies around the value set by the frequency knob. The Q-factor automatically increases with larger gain values (either negative or positive) so that the perceived volume remains fairly constant.
narrow bell: the gain knob controls the amplitude of frequencies around the value set by the frequency knob. High Q-factor!
hishelf: classic high-shelf filter. The gain knob controls the amplitude of frequencies above the value set by the frequency knob.
A low-shelf filter specially designed for bass frequencies. It is not fully tunable, but is significantly more precise than conventional models. Click on the button to select a frequency, then adjust the attenuation/amplification using the bottom knob (the range is +/- 24 dB).
In addition to the three classic EQ filter bands, Uhbik-Q has two quasi brick-wall filters, with a choice of several fixed frequencies below/above which very little of the signal will pass. They are useful for eliminating e.g. rumble and hiss, leaving the other bands free for other tasks.
The upper left gain knob normally controls the output level (the range is +/- 24 dB), but you can use the selector to turn it into the gain of an extra filter instead:
wide mids: A very wide midrange frequency band, covering almost the entire audible spectrum. Only very low and very high frequencies remain unaffected.
center bell: A bell-shaped band (like the flex bell option of the two semi-parametric bands) whose frequency is exactly between the band 1 and band 2 frequencies. Of course the width also depends on bands 1 and 2. Although these dependancies seem limiting, having an extra filter between the others can be very useful.
Why are the frequencies of the two main bands freely adjustable, while their Q-factors are not?
Answer: tunable frequency bands can be ‘modulated’ at will via automation. This transforms Uhbik-Q into a highly flexible creative tool. Early ideas about more bands and more control were dropped in favour of wider, more promising horizons. Note that several reputable hardware simulations only switch the frequencies!