EE4209/EE5809 Digital Audio Technology

Speex: A Free Codec For Free Speech

http://www.speex.org/
Speex: A Free Codec For Free Speech

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Speex is an Open Source/Free Software patent-free audio compression format designed for speech.

The Speex Project aims to lower the barrier of entry for voice applications by providing a free alternative to expensive proprietary speech codecs.

Moreover, Speex is well-adapted to Internet applications and provides useful features that are not present in most other codecs. Finally, Speex is part of the GNU Project and is available under the revised BSD license.

http://en.wikipedia.org/wiki/Speex

Unlike many other speech codecs, Speex is not targeted at cellular telephony but rather at Voice over IP (VoIP) and file-based compression.

The design goals have been to make a codec that would be optimized for high quality speech and low bit rate.

To achieve this the codec uses multiple bit rates, and supports ultra-wideband (32 kHz sampling rate), wideband (16 kHz sampling rate) and narrowband (telephone quality, 8 kHz sampling rate).

Since Speex was designed for Voice over IP (VoIP) instead of cell phone use, the codec must be robust to lost packets, but not to corrupted ones.

All this led to the choice of Code Excited Linear Prediction (CELP) as the encoding technique to use for Speex.[6] One of the main reasons is that CELP has long proven that it could do the job and scale well to both low bit rates (as evidenced by DoD CELP @ 4.8 kbit/s) and high bit rates (as with G.728 @ 16 kbit/s).

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