Telephony-audio robustness: why 8kHz narrowband calls break generic STT

Traditional 8kHz telephony audio limits captured frequencies to roughly 300–3400 Hz, removing high-frequency phonetic information that many generic 16kHz speech-to-text models rely on, particularly for sounds such as fricatives; simply upsampling the audio cannot restore information absent from the original recording. The article argues that codec compression, packet loss, and packet-loss concealment further degrade transcription and speaker-diarization performance, with resulting errors disproportionately affecting names, account numbers, product terms, and other data essential to downstream CRM and NLU workflows. It recommends benchmarking models on representative production recordings across codecs, accents, noise levels, languages, and controlled packet-loss conditions, while measuring entity extraction, intent classification, diarization, and business-process accuracy in addition to word error rate. It concludes that models trained on genuine degraded telephony data are better suited to these conditions than wideband models or models trained only on downsampled clean audio, and promotes Gladia’s Solaria-3 and related API services as a specialized option, alongside information about pricing, compliance, and asynchronous diarization.

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