The hard cases in speaker diarization: overlap, short turns, and noise
Blog post from AssemblyAI
Speaker diarization, which identifies who spoke when, performs well in clean two-person recordings but faces recurring difficulties in real conversations, particularly overlapping speech, short back-channel responses, background noise, far-field recordings, and errors in estimating the number of speakers. Overlap is especially challenging because many systems assume only one active speaker at a time, potentially dropping one speaker’s words, while brief reactions such as “yes” or “exactly” can be assigned to the wrong person without substantially affecting the conventional time-weighted diarization error rate (DER). The piece argues that concatenated minimum-permutation word error rate (cpWER), paired with speaker count error, better captures word-level attribution mistakes and speaker merges or splits. It describes AssemblyAI’s Universal-3.5 Pro as a joint transcription-and-diarization model designed around cpWER, with streaming revisions for real-time use and noise-suppression settings intended for near-field and far-field audio, while citing comparative performance and pricing claims.
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