Shelves is a voltage-controlled signal processor inspired by the EQ section of console channel strips. Just like many sought-after equalizers, it provides low-shelf, high-shelf, and two parametric tone controls. Unlike an equalizer, each of these four tone controllers can be swept over the entire audio range; and their parameters can be freely modulated with control voltages.
Shelves occupies a space between tone-controllers and filters, sometimes achieving sounds reminiscent of a filter bank. It provides a subtler and less cliché'd way of spectrally altering complex drones or feedback patches.
Shelves is designed for Eurorack synthesizer systems and occupies 16 HP of space. It requires a -12V/+12V supply (2x5 connector), consuming 75mA from the -12V rail and 75mA from the +12V rail. The red stripe of the ribbon cable must be oriented on the same side as the "Red stripe" marking on the printed circuit board.
Controls, inputs and outputs
A. High-shelf section. This section boosts or attenuates all frequencies above the FREQ control. The GAIN potentiometer controls the amount of attenuation or boosting. No modification is applied when GAIN is in its central position.
B. Parametric sections 1&2. These two sections boost or attenuate all frequencies in a frequency band whose central frequency is set by FREQ. The narrowness of this frequency band is set by the Q setting - from very wide to very selective.
C. Low-shelf section. This section boosts or attenuates all frequencies below the FREQ control. The GAIN potentiometer controls the amount of attenuation or boosting. No modification is applied when GAIN is in its central position.
1. 2. Global frequency and gain CV inputs. These CV inputs simultaneously adjust the FREQ or GAIN of all 4 channels.
3. IN. Audio input. The input signal can optionally be attenuated by -6dB before being processed by the EQ filter. A jumper is available on the back of the module to enabled/disable this pre-gain.
4. Output clipping indicator. It is recommended to reduce the level of the input signal - or to reduce the gain on all channels - when this LED lights up.
5. OUT. Audio output.
6. 7. Individual outputs for the parametric sections' filters. Behind the scenes, Shelves' parametric sections are full-blown multimode filters. The low-pass (LP), band-pass (BP), and high-pass (HP) outputs of these two filters are provided on these two groups of jacks.
Note: the first batch of modules had these two groups of three outputs on a separate expansion module. Please refer to the last section to learn how to connect it to the main board.
Ranges and scales
On all sections, the FREQ knob spans the entire audio range, from 20 Hz to 20 kHz.
The FREQ CV input has a 1V/Oct scale and acts as an offset to the value set by the FREQ knob.
The GAIN knob covers an attenuation/boost range of -15dB to +15dB.
The GAIN CV input has a 3dB/V scale and acts as an offset to the value set by the GAIN knob.
Gains above +15dB cannot be reached, even by adding a positive CV offset to the GAIN CV input. However, gains below -15dB can be obtained by adding a negative CV offset to this CV input.
On the two parametric sections, the Q parameter, which controls filter selectivity, goes from 1 to 10, but can reach much higher values with CV modulation.
The first batch of modules had the two groups of HP/BP/LP outputs on a separate expansion module. The expander is provided with two cables. Check that they are connected like on these pictures (observe the orientation of the red stripe):