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Message: [QUOTE="Shamiso, post: 92588, member: 160"] DeltaScope 1.2 brought an AAX build to Pro Tools, but Pro Tools still feeds AAX key inputs as mono. The limitation matters if you want DeltaScope to compare two stereo signals rather than simply receive a summed reference. You can still use a key input for straightforward checks, especially when the reference is mono or when left-right detail is irrelevant. The catch begins when [B][URL='https://goldmidi.com/community/threads/apollo-view-expands-deltascope-to-windows-and-aax.77962/']DeltaScope’s new AAX support[/URL][/B] meets a genuinely stereo source. A mono key preserves some overall energy, but it no longer carries the original left and right channels as separate signals. The mismatch is easy to miss because the plugin can open, receive audio, and look completely normal. Nothing has crashed. The problem is simply that the comparison entering DeltaScope is no longer the same stereo pair you meant to inspect. [HEADING=2]A mono key cannot preserve every stereo difference[/HEADING] A stereo signal is not just two level readings glued together. Left and right can contain different transients, different reverberation, different phase relationships, different panning, and completely different material. Folding those channels to one key input combines information before DeltaScope ever sees it. Simple material may survive that reduction well enough. A centered kick, bass, or vocal with nearly identical left and right content will usually leave little ambiguity. Wide synths, stereo reverbs, doubled guitars, overheads, ambience, and master-bus material are another story. Phase is the nasty part. Two channels can contain strong energy individually while partially cancelling when summed. The same issue appears in [B][URL='https://doi.org/10.1109/ICASSP.2006.1661329']stereo-to-mono downmixing behavior[/URL][/B], where interchannel phase differences affect what survives the reduction. Once cancellation happens in the key path, DeltaScope cannot reconstruct the lost left-right relationship from the mono result. You can end up chasing a strange residual that belongs to the routing rather than the processor. A wide chorus might look less different than it really is. A stereo delay can lose alternating information. One side of a reverb tail may simply disappear into the combined key. [HEADING=2]Linked instances keep the stereo pair intact[/HEADING] DeltaScope has another route that avoids the mono-key bottleneck. Put one instance on each signal you want to compare and use the plugin’s instance-linking system instead of feeding the second signal through Pro Tools’ key input. The linked instances share audio directly inside the plugin workflow and identify available sources by track name. You keep the stereo channels separate, which means Delta mode, overlay views, phase correlation, and spectrum comparison can work from the actual pair instead of a mono reduction. A practical setup is boring, which is good. Put one DeltaScope instance on the reference track and another on the processed track. Give the tracks clear names, select the reference from the linked source inside the comparison instance, then play a section that contains real stereo information. Start with something obviously asymmetric if you want to confirm the routing. A percussion hit panned hard left followed by another on the right makes a useful sanity check. If your comparison path has collapsed to mono somewhere, the display will tell on it fast. Automatic delay compensation inside DeltaScope also matters here. Two tracks can pass through different plugin chains and arrive with different latency, so a sample offset can create a large residual even when the tonal processing is identical. Let the analyzer correct the offset before treating what remains as a processing difference. [HEADING=2]The key input still has useful jobs[/HEADING] None of this makes the Pro Tools key input useless. Mono sidechains are perfectly sensible for detector-style jobs where a plugin only needs one control signal. Kick-driven compression is the obvious case, and plenty of gates, triggers, duckers, and envelope followers work fine with exactly that arrangement. DeltaScope asks a different question when you use it as a stereo comparator. You are not merely asking whether a control signal is present. You are asking how two complete signals differ in time, level, frequency, and phase. For mono sources, the ordinary key path stays convenient. For stereo material, linked instances preserve the information you actually care about. The distinction becomes especially important on master buses, stereo effects returns, drum overheads, parallel chains, and any processor that changes width or channel relationships independently. AAX support puts DeltaScope inside Pro Tools without needing another host, but the host’s mono key architecture still sets the rules for that input. Instance linking works around the limitation without pretending the summed key is the same thing as a true stereo feed. [/QUOTE]

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