Only about 20% of target speech time-frequency units are needed for near-normal intelligibility.

Evidence

An analysis of the local SNRs of all T-F units in ten unfiltered stimuli (see Fig. 3 ) was performed to determine the proportion of T-F units exceeding a certain SNR level. The analysis reveals that on average only about 20 % of the total target T-F units exceeded a local SNR value of –4 dB and about 7 % exceeded a value of 10 dB SNR. This corresponds to the proportion of target speech that was retained in the final signal at the SNR criteria mentioned. Note that at the criterion of ‑4 dB no decrease in speech intelligibility was observed as compared to the condition with intact target speech. This analysis thus demonstrates the sparse character of speech and the fact that only little target speech was needed to achieve a reasonable performance on this experimental task with a restricted speech vocabulary. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1619