Latency and anchor dependence in objective binaural quality metrics: a cross-format evaluation of immersive audio

Immersive audio formats compete for adoption, yet objective comparisons across them remain limited, and the behaviour of the objective models under cross-format conditions is largely uncharacterised. This study applies two binaural models, BAM-Q (perceptual quality) and BINAQUAL (localization similarity), to binaural renderings of 11 format variants derived from 3 professional recordings differing in genre and Ambisonic provenance, under three reference anchors and with a controlled test of stimulus alignment. Two properties of the evaluation influence the outcome more strongly than many format differences, and affect the two models differently. First, immersive renderers impose transport delays up to 510 ms that are not quality degradations; because BINAQUAL compares phase representations, leaving them uncompensated makes its score track delay rather than fidelity ( ρ = − 0.86 ), and correcting them changes localization similarity by a median of 149.3%. BAM-Q, operating on modulation-domain representations, is unaffected (median 0.0%). Second, under BINAQUAL the apparent advantage of one format family over another depends on the reference anchor, reversing in all 3 items when the channel-based anchor replaces a scene-based one; the BAM-Q composite never reverses. With aligned stimuli the models are moderately correlated ( r = 0.51 ), not independent. Format orderings are reproducible across content (Kendall’s W = 0.94 for localization similarity, permutation p < 0.001 ). The results yield prescriptions for cross-format evaluation (compensate and report latency, treat the anchor as an experimental factor, refer cue measures to discrimination thresholds) and identify subjective validation as the next step.