Thursday, October 29, 2009


Our ability to understand speech can be measured.  The most common method is to select random syllables and ask a group of listeners to write them down, then mess up the audio (muffle the sound by lowering the bandwidth, for example), and run the test again.  When this is done the result looks like this

This picture shows that as we pass more and more of the sound by raising the cut-off frequency, the listener’s accuracy also increases.  This makes sense; we all know it’s hard to understand someone who’s very muffled, and it gets easier when they speak clearly.  That’s why wideband audio in telephony is so important:  with normal phone fidelity – 3 kHz – people make mistakes on one out of ten syllables!   By raising the cut-off to 7kHz with HD Voice, the chart's red line shows this rises to nearly 100%.  And in real-world settings, like accented speech, speakerphones, people sitting too far away, the difference is even more dramatic.

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