LAP TSL-E26
A stepped three-band equaliser built as a component-level circuit model: the whole board - three band stages, each a resistor ladder loaded by an active resonator, the HF CUT low-pass and the output stage - is solved as a circuit in real time. Two channels, two units with their own component tolerances.
How it works - and how it differs from a plugin EQ. TSL-E26 is a stepped equaliser and the controls mean what they meant on the unit. Three bands with stepped gain (±15 dB in 3 dB steps) at switched frequencies (LOW 63 Hz – 1 kHz, MID 0.7 – 4 kHz, HI 2.8 – 11 kHz), each band a resistor ladder loaded by an active resonator. There is no Q control and the Q is not constant: the bell gets wider as the gain gets smaller - about Q 0.8 at ±15 dB, 0.5 at ±9 dB and only 0.31 at ±3 dB, so a small correction is a very broad one. The three stages are in cascade and add up where they overlap. SHELF turns the LOW or HI band into a 6 dB/octave shelf hinged at the selected frequency. HF CUT is a second-order (12 dB/oct) low-pass with −3 dB at 13 / 8.3 / 6.5 / 4.1 kHz. BYPASS is EQ OFF: the resonators are disconnected and the board passes flat. The board clips at about +1 dBFS, so large boosts on hot signals clip inside the EQ as they would in the hardware. The two channels are two units with their own component tolerances.
The whole board, solved live
Not an EQ algorithm: the board is solved as a circuit at sample rate - op-amps with real bandwidth and offsets, and every resistor and capacitor with its own tolerance. The two channels are two units, so their centre frequencies and gains differ slightly, as two real units do. Turning a switch moves the contacts inside the simulated board; the curves fall out of the components.
Stepped bands, no Q control
LOW 63 Hz - 1 kHz, MID 0.7 - 4 kHz and HI 2.8 - 11 kHz, each with GAIN ±15 dB in 3 dB steps. The Q is not constant: the bell widens as the gain gets smaller - about Q 0.8 at ±15 dB and 0.31 at ±3 dB, so a small correction is a broad one. The three stages are in cascade and add up where they overlap.
SHELF · HF CUT · BYPASS
SHELF rewires the resonator of LOW or HI into a 6 dB/oct shelf hinged at the selected frequency - click the LED above GAIN. HF CUT is a 12 dB/oct low-pass with -3 dB at 13 / 8.3 / 6.5 / 4.1 kHz, LIN takes it out. BYPASS is EQ OFF: the resonators are disconnected and the board passes flat.
Headroom of the board
The output stage of the board clips at about +1 dBFS, so large boosts on hot signals clip inside the EQ as they would in the hardware - turn the source down in front of it. Below clipping the board is linear and very clean.
Two channels, LINK
Two independent units with their own controls. The ON / OFF switch is LINK: channel 2 follows channel 1 for stereo; switch it off for dual mono.
Output transformer · SATURATION
After the board can sit a model of a real audio output transformer - the core with its magnetisation and hysteresis solved sample by sample - for weight in the low end and low-order harmonics that grow with the bass and the level. SATURATION drives it from -12 to +18 dB without changing the level. Off by default - switch TRAFO ON in the settings menu.
Settings menu
Right-click the panel: window SCALE 80 / 100 %, OVERSAMPLING 1x / 2x / 4x, TRAFO OFF / ON and SATURATION (one row per channel when LINK is off). Everything can be changed while playing - the board is rebuilt in the background and cross-faded in, without a drop-out.
Presets
A preset bar above the panel: categories, Save / Save as / Delete and ◀ ▶ to step through the settings. A preset holds the switches and the menu settings; the selected preset is saved with the project. One plain file per preset - copy them between machines and systems.
Light on CPU
About 1 % of a CPU core for a stereo instance at the default 2x oversampling, about 7 % with the output transformer on - light enough for every track of a session. Oversampling is counted from 44.1 / 48 kHz, so a 96 or 192 kHz session has the same sound and load.
First release. Three stepped bands (±15 dB in 3 dB steps) at switched frequencies, SHELF for LOW and HI, HF CUT, BYPASS = EQ OFF and LINK; a model of a real audio output transformer (off by default) with SATURATION -12 … +18 dB; oversampling 1x / 2x / 4x (default 2x); presets that include the right-click menu settings and are saved with the project.