VoxReason: Listener-Free Evaluation of Source-Grounded Speech Planning Before Synthesis

Abstract

Expressive speech systems have to decide how an utterance is delivered before any waveform is rendered. In dialogue agents, narration, and role-conditioned TTS, that planning step sets affect, pitch, energy, rate, pause, emphasis, and stance, yet standard audio metrics rarely show whether those choices were actually licensed by the source record. This leaves a practical evaluation gap: a system may sound plausible while relying on a memorized script instead of the cue that governs delivery. VoxReason casts this pre-synthesis step as a listener-free task for source-grounded speech planning. Systems output a source-cited speaking plan, and a deterministic verifier checks citation legality, slot agreement, unsupported state, schema validity, and one-cue counterfactual locality. On 1,440 checked source-label cases, shortcut controls show why slot accuracy alone is unsafe: a key-lookup oracle reaches 1.000 plan-slot accuracy on seen keys, while an emotion prior still reaches 0.958 slot accuracy on source-key-disjoint cases without citing intensity or identity. In a separate 100-case learned source-key-disjoint comparison, a 7B locality SFT+CF repair improves plan-slot accuracy/locality from 0.684/0.141 to 0.919/1.000, and removing source records lowers citation-required grounded score by 0.488. The resulting benchmark isolates whether planned delivery is warranted by the record before waveform evaluation or listener studies are used.