Age-related hearing loss is the leading sensory deficit in older adults, yet audiometric thresholds at conventional frequencies often poorly predict speech understanding. Two competing hypotheses have emerged: extended high-frequency (eHF) hearing loss beyond 8 kHz may unmask variance in speech performance, while hidden hearing loss from cochlear synaptopathy---detectable via auditory brainstem response (ABR) wave I amplitude reduction---may degrade temporal coding independent of audiometry. Here, in 526 ears from 263 tinnitus-free adults in the Swedish Tinnitus Outreach Project (STOP) cohort, we show that eHF pure-tone average (10–16 kHz) is the single most age-sensitive auditory measure, explaining 64% of age-related variance (R² = 0.64) compared to only 16% for conventional audiometry (R² = 0.16). Moreover, eHF thresholds robustly predict both word and phoneme recognition in speech-weighted noise (+4 dB SNR), explaining 34–36% of speech variance (R² = 0.34–0.36)—substantially exceeding conventional pure-tone average (22–25%) and all ABR features (5–13%). In contrast, ABR Wave I amplitude—the putative marker of cochlear synaptopathy—contributes no additional explanatory power even in high-reliability recordings (ICC = 0.96). These findings challenge the translational relevance of cochlear synaptopathy to age-related speech deficits and suggest conduction delays, not synaptic loss, as the peripheral neural mechanism underlying speech comprehension decline in aging.

CRC was supported in 2020 by the UK National Institute for Health Research (NIHR) Biomedical Research Centre but the views expressed herein are his own and do not represent those of NIHR nor the UK Department of Health and Social Care. CRC is also a member of the Scientific Advisory Board of the American Tinnitus Association and member of the Professional Advisory Committee of the Tinnitus UK.

This analysis was not funded. The auditory data acquisition was supported by grants from the Swedish Research Council (K2014-99X-22478-01-3) and Tysta Skolan.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study was approved by the Regional Ethics Review Board in Stockholm (Dnr: 2016/1468-31/2); all participants provided written informed consent.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes