The signal loop is the feedback cycle between the ad account and the studio. Every batch launches into a clean testing structure, results get read per angle and concept rather than per ad, and the learnings decide what the studio makes next week.
Run long enough, the loop compounds: the account gets sharper about what to say, and production gets faster at saying it. It is also why in-house creative matters, a loop that routes through a third agency's backlog is not a loop, it is a queue.
