These are then passed through a two-channel transmission medium (usually an LP record) before being decoded back to four channels and presented to four speakers.

His basic formula used 90 degree phase shift circuitry to enable enhanced 4-2-4 matrix systems to be developed.

By the time that the most advanced logic system was introduced for SQ, the Tate Directional Enhancement System,[6] by Martin Willcocks and Peter Scheiber, realized into the superb Tate II 101A decoder by Jim Fosgate, "quad" was already considered a failure.

Of Pink Floyd's The Dark Side of the Moon, engineer Alan Parsons recalled: "It was certainly the band's intention, when we recorded the album, to mix in quad.

It matrixed the four outputs of the SQ decoder to derive additional signals and compared their envelopes to detect the predominant direction and degree of dominance.

A processor section, implemented outside of the Tate IC chips, applied variable attack/decay timing to the control signals and determined the coefficients of the "B" (Blend) matrices needed to enhance the directionality.

Since the DES could recognize all three directions of the Energy Sphere simultaneously, and enhance the separation, it had a very open and 'discrete' sounding soundfield.

Dolby used the Tate DES IC's in their theater processors until around 1986, when they developed the Pro Logic system.

The Fosgate used a faster, updated version of the IC, called the Tate II, and additional circuitry that provided for separation enhancement around the full 360° soundfield, using the Haas effect.

In order to maintain the highest quality levels, Fosgate used hand-sorted ICs and 1% -tolerance components, and each decoder was hand-optimized.

Unlike earlier Full Wave-matching Logic decoders for SQ that varied the output levels to enhance directionality, the Tate DES cancelled SQ signal crosstalk as a function of the predominant directionality, keeping non-dominant sounds and reverberation in their proper spatial locations and at their correct level.