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Message: [QUOTE="Bombastus, post: 92329, member: 2178"] Portico II lets you move the compressor detector from the input side of the gain-control element to the output side with its FF/FB switch. In Feed-Forward mode, the detector sees the signal before compression changes it. In Feed-Back mode, the detector watches a signal that the compressor has already altered. The change reaches deeper than tone. Rupert Neve Designs documents the hardware’s marked ratio values as applying to Feed-Forward operation, while Feed-Back mode reduces the effective ratio range because the detector sits inside the control loop. The plug-in is presented as a faithful recreation of that hardware behavior, so treating a displayed four-to-one setting as an identical four-to-one experiment in both modes misses what the switch is doing. [HEADING=2]Detector position changes the control loop[/HEADING] A feed-forward compressor makes its decision from the incoming signal. The detector can measure how far the input has crossed the threshold and send a control signal forward to the VCA without waiting to observe the result. This topology makes it comparatively straightforward to impose a chosen relationship between input change and output change. Feedback compression closes the loop. The detector measures the output after gain reduction, then uses that already-reduced level to decide how much control action should happen next. An [B][URL='https://patents.google.com/patent/US5444788A/en']audio compressor with feedback and feed-forward control[/URL][/B] describes the same basic distinction, including the way a feedback loop can make ratio behavior harder to define independently from the rest of the control system. Portico II packages both approaches behind one button, which makes the comparison look simpler than it is. Attack, release, threshold, and ratio can remain visually unchanged while the detector has moved to a different point in the circuit. You have not changed one flavor control. You have changed what information the compressor uses to govern itself. [HEADING=2]Feedback mode makes the ratio marking less literal[/HEADING] RND’s documentation calls out an easy detail to miss. The ratios printed for the Portico II are available in Feed-Forward operation, while Feed-Back operation reduces the overall compression-ratio range represented by those markings. A knob parked at the same position therefore does not guarantee the same effective slope once you switch topology. This is why the [B][URL='https://goldmidi.com/community/threads/portico-ii-m-s-mode-changes-the-compressor.77716/unread']Portico II compressor response controls[/URL][/B] should not be compared by freezing every knob and judging only the FF/FB button. Keeping the controls fixed is useful for hearing the topology change, but it is not proof that both versions are producing equal gain reduction. One mode may simply be compressing less because its effective ratio has changed. A better comparison starts with the meters. Set Feed-Forward for a modest amount of reduction on a representative loud section, then switch to Feed-Back and adjust threshold or ratio until the gain-reduction amount is reasonably close. Level-match the output afterward. Only then are you in a better position to decide whether the envelope feels different rather than merely reacting to a change in compression depth. This matters most when people describe Feed-Back as automatically softer, warmer, or more relaxed. Some of that impression can come from topology, but some can also come from using less effective compression at the same visible ratio setting. A fair listening test has to separate those two effects before attaching a character label to the switch. [HEADING=2]Attack and release stop being isolated comparisons[/HEADING] Detector location also changes the context around attack and release. In Feed-Forward mode, the detector follows the uncompressed input envelope, while Feed-Back mode follows an output envelope that is continuously being changed by the compressor itself. The timing controls may carry the same labels, but they operate inside different control relationships. Fast transient material exposes this quickly. A snare, kick, or clipped percussion peak can push the feed-forward detector from the full incoming excursion, while the feedback detector observes the consequence after gain control has begun reshaping the output. Matching nominal attack and release values therefore does not guarantee identical transient handling. The practical mistake is chasing a preferred mode with numbers instead of behavior. If Feed-Back feels too loose, raising the displayed ratio alone may still leave you comparing a different effective slope from Feed-Forward. If Feed-Forward feels too pinned down, lowering its ratio may change more than the topology you originally wanted to judge. Use the gain-reduction meter, output level, and the front edge of transients as three separate checks. Match reduction before judging punch, match loudness before judging tone, and listen to how quickly the mix settles after a loud event. The FF/FB switch becomes far more useful once the printed ratio stops being treated as a promise that both control loops are doing the same amount of work. [/QUOTE]

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