Institute for Telecommunication Sciences / Research Topics / Audio Quality Research / Public Safety Audio Quality / Speech Intelligibility Demo (Listen)

Speech Intelligibility Demo (Listen)

Project Description

The PSCR program, with support from DHS S&T, studied the intelligibility of speech that is encumbered with background noise and then digitally encoded. The Listen tab that follows provides some example MRT recordings from the study.

Audio codecs provide efficient (low data rate) digital representations of audio signals. When the signal is speech alone, a speech-specific signal model leads to efficient coding with good intelligibility. But when significant levels of background noise are combined with speech, broader or more robust signal models are required and these in turn typically require higher data rates. Thus one will expect to experience higher intelligibility for the examples that use higher bit-rates.

Audio Details and Samples

The Learn page provides a guide to the terms describing the samples. This page presents audio samples you can play for various codecs, bands, and bit rates.

» See the resulting report: NTIA Technical Report TR-15-520 Speech Codec Intelligibility Testing in Support of Mission-Critical Voice Applications for LTE.


Codec Bit Rate Narrowband



FM Not Applicable Not Applicable Not Applicable
P25-HR 2,450 Not Applicable Not Applicable
P25-FR 4,400 Not Applicable Not Applicable
AMR 4,750 Not Applicable Not Applicable
EVS 5,900 Not Applicable
Opus 5,900 Not Applicable
AMR 12,200 Not Applicable Not Applicable
AMR-WB 12,650 Not Applicable Not Applicable
EVS 13,200 Not Applicable
Opus 13,200 Not Applicable
AMR-WB 23,850 Not Applicable Not Applicable
EVS 24,400
Opus 24,400

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