The G23-SD is the dynamic evolution of the G23-S: a dual-technology stereo tone control and dynamic equalizer that brings three processing concepts together in a single 19″ rack unit (3U) – a Linear Tilting Equalizer, a Baxandall tone control and two independent dynamic push circuits, one for the tilt and one for the midrange. All three can be used on their own or in combination.
Linear tilt – without a pivot
Most tilt equalizers cross two conventional 6 dB/oct filter curves. That concentrates phase shift and group delay around a single crossover frequency, which can make processed material sound localised or worked, particularly at higher settings. The G23-SD takes a different approach: it approximates a genuine 1 dB/oct linear slope across the entire audio spectrum, so the unavoidable phase side effects are spread evenly from 20 Hz to 20 kHz instead of being clustered in one region. Even at extreme settings, material tends to retain its original balance and subjective character.
Because the slope is linear, there is no pivot or corner frequency to select – the transfer function is universal. A single centre-detented LINEAR TILTING control sets the slope up to ±1 dB/oct, equivalent to approximately ±4 dB at the outer limits of the audio spectrum: clockwise brightens, counter-clockwise darkens.
Baxandall tone control
Three centre-detented boost/cut controls add a gentle Baxandall-style tone section: LOW (±6.5 dB, wide shelving curve), MID (±2 dB, wide bell curve) and HIGH (±4 dB, wide shelving curve). A three-position frequency selector beneath each control sets the operating range of the band. The frequencies were chosen through extensive listening tests for optimum performance in the unobtrusive category.
Dynamic push circuits
The G23-SD adds level-dependent behaviour to the tone controls. Tilt Push is a combined ratio/threshold control that pushes the tilt toward brighter (clockwise) or darker (counter-clockwise) as the signal level rises. Mid Push progressively attenuates the mid band as a function of signal level, by up to approximately 3 dB; its sidechain is weighted to the midrange (around 300 Hz – 4 kHz) and is relatively insensitive to deep bass or high-frequency content. Each circuit has its own RELEASE control, from very fast to quite slow, and two gain-reduction meters show what the circuits are doing.
Both circuits work by shunting the relevant control potentiometers with precision-selected, optically isolated vactrols. This provides 100% galvanic isolation between the audio and the control circuits. With both push controls set to OFF, the unit is electrically identical to the G23-S.
Tube or solid state – you choose
In TUBE mode the signal passes through Lundahl audio transformers with internal electrostatic shielding at input and output, and a pure class-A topology based on two closely matched 6N23H tubes in the feedback chain of the linear slope filter. No solid-state devices are in the signal path in this mode. In SOLID mode the transformers are bypassed and the circuit is wrapped in servo-balanced active electronics at input and output, offering enhanced headroom and very high drive capability.
A three-position BYPASS switch selects TUBE, SOLID or OUT – a full relay bypass with the input XLR shorted directly to the output XLR, leaving no electronics in the signal path. The TRIM control adjusts the output gain of the processed signal for level-matched A/B comparison against the bypassed signal.
Built for analogue levels
The G23 was originally developed for use with analogue tape, and its optimum operating range reflects this. The nominal operating level is +4 dBu, with approximately 14 dB of headroom before the tube path begins to saturate (around 15 Vpp AC output) – and beyond that point it saturates progressively rather than clipping hard. For modern DAW systems, the recommended analogue level for 0 dBFS is +10 dBu to +12 dBu, in both tube and solid-state mode.
