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Speech Enhancement Tutorial - Evaluation Methods

2.2 Speech Intelligibility

There are two categories of evaluation techniques for speech intelligibility:

Subjective Measures:

Objective Measures:

When assessing the intelligibility of a speech signal, we need to choose an appropriate linguistic level at which to make measurements. Should we measure the accuracy with which each phonetic element is communicated? Or whether each word is identifiable? Or whether the meaning of a sentence can be understood?

The problem is one of increasing redundancy: not all phonetic sequences make up words in the language, not all word sequences make up meaningful sentences. You don't need to correctly identify all segments to identify a word, and you don't need to identify all words to understand a sentence!

This linguistic redundancy introduces another problem in that individual human listeners will vary in their ability to make use of these linguistic constraints. While we may want to assess the utility of a channel to convey the meanings of real spoken utterances, listeners will vary widely in their ability to understand the speech depending on their own linguistic competence. Thus most speech intelligibility tests are either of phonetic units made up into nonsense syllables, or words in isolation or in short sentences.

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