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Message: [QUOTE="Bombastus, post: 91936, member: 2178"] The Fairchild 670 can split a stereo signal into lateral and vertical components, limit them separately, then rebuild conventional left and right outputs. On the original hardware, one switch changes the machine from two independent left/right limiters into a matrixed stereo processor. Lat/Vert is usually translated as mid/side today, but the old wording came from disc cutting rather than modern plug-in menus. Lateral signal represents the sum of left and right, while vertical signal represents their difference. A 1958 stereophonic recording patent describing [B][URL='https://patents.google.com/patent/US3013125A/en']lateral and vertical groove modulation[/URL][/B] assigns those two components to different physical directions in the record groove. Calling the channels “center” and “sides” is convenient, yet it can make the mode sound simpler than it is. A hard-panned guitar contributes to both the sum and difference channels, while a perfectly identical signal in left and right disappears from the difference channel. Lat/Vert therefore gives you control over stereo relationships, not two neat buckets containing center instruments and edge instruments. [HEADING=2]Lat/Vert mode separates sum from difference[/HEADING] The 670’s matrix does the important work before either limiter acts. Left plus right feeds the lateral path, left minus right feeds the vertical path, and a second matrix converts the processed components back into left and right afterward. The original manual describes the two limiter sections as independent in this mode, which matters because unequal gain reduction changes the balance between summed and difference information. Push the vertical path harder and wider, out-of-phase, or strongly differential material can recede relative to the center. Work the lateral path harder and the opposite can happen, with the difference component becoming more prominent after recombination. Neither move is equivalent to grabbing a stereo-width knob because the amount of change follows the music and the limiter’s gain reduction. Vinyl mastering explains why Fairchild bothered with the arrangement. Large vertical groove movement was harder to track and could consume useful groove space, so controlling lateral and vertical amplitudes separately had a practical cutting-room purpose. The same geometry makes Lat/Vert useful in digital work, but the physical problem that inspired it was a record groove, not a desire to make mixes artificially wider. [HEADING=2]Independent processing can preserve position without freezing width[/HEADING] Independent left/right compression can pull the apparent image around when one side triggers more gain reduction than the other. Lat/Vert avoids that particular left-versus-right tug because the processor works on symmetrical sum and difference components instead. A vocal panned slightly left is no longer being treated as a left-channel event in the same simple sense. A hard-right transient makes the distinction easier to hear. In independent left/right operation, enough gain reduction on the right channel alone can drag the image toward the left for a moment. Split the same event into lateral and vertical components, and its position depends on how those two components are reduced and recombined, rather than on one speaker channel simply being turned down. Width can still move. Different gain reduction on the lateral and vertical paths changes their ratio, so the reconstructed stereo field can breathe inward or outward as the program changes. The useful distinction is between image drift caused by unequal left/right attenuation and deliberate or incidental width change caused by unequal sum/difference attenuation. The Time Constant switches still determine the limiter’s envelope behavior, so [B][URL='https://goldmidi.com/community/resources/fairchild-670-compressors-attack-and-release-times.49/']Fairchild 670 attack and release settings[/URL][/B] remain relevant once you choose Lat/Vert. Their job does not change into “mid attack” and “side release.” Each limiter section simply applies its own timing to a different signal component after the matrix. [HEADING=2]Modern emulations add controls the hardware never had[/HEADING] A plug-in labeled Fairchild 670 may expose more routing choices than the original chassis. Universal Audio, for example, provides linked and unlinked sidechain options around the Lat/Vert architecture, while the vintage manual describes the hardware mode as independent limiting of the two matrixed components. Treat the mode selector and any link control as separate decisions instead of assuming Lat/Vert automatically means one fixed stereo behavior. Input gain can hide another wrinkle. On Universal Audio’s current model, the two Input Gain controls continue to act on left and right before the Lat/Vert matrix, even though the Threshold and Time Constant controls are associated with the lateral and vertical limiter paths. Turning one input control is therefore not the same operation as turning a dedicated Mid or Side trim after encoding. You can hear the difference most clearly with material that contains a stable center and active stereo detail. A centered vocal with wide room microphones, doubled guitars, or stereo reverbs gives the vertical path something meaningful to react to without reducing Lat/Vert to a novelty widening trick. Keep the gain reduction asymmetric only when you actually want the stereo relationship to move, because the matrix will faithfully turn every imbalance between those two limiter paths back into audible left/right behavior. [/QUOTE]

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