CELT 0 votes

The CELT codec is a compression algorithm for audio. Like MP3, Vorbis, and AAC it is suitable for transmitting music with high quality. Unlike these formats CELT imposes very little delay on the signal, even less than is typical for speech centric formats like Speex, GSM, or G.729.

Using CELT application developers can build software that allows musicians to perform together across the Internet, or simply build great sounding telephony systems. Why shouldn't your telephone sound as good as your stereo?

Like other open and unencumbered technology from the Xiph.Org Foundation CELT requires no royalties and no complicated licensing.

CELT stands for “Constrained Energy Lapped Transform”. It applies some of the CELP principles, but does everything in the frequency domain, which removes some of the limitations of CELP. CELT is suitable for both speech and music and currently features:

1. Ultra-low latency (typically from 5 to 22.5 ms)
2. Full audio bandwidth (≥20kHz; sample rates from 8 kHz to 48 kHz)
3. Support for both speech and music
4. A quality/bitrate trade-off competitive with widely used high delay codecs
5. Stereo support
6. Packet loss concealment
7. Constant bit-rates from 32 kbps to 128 kbps and above
8. A fixed-point version of the encoder and decoder

The CELT codec is meant to bridge the gap between Vorbis and Speex for applications where both high quality audio and low delay are desired.

internet Speech Audio Codec(ISAC) 0 votes

internet Speech Audio Codec (iSAC) is a wideband speech codec, developed by Global IP Solutions (GIPS) (acquired by Google Inc in 2011). It is suitable for VoIP applications and streaming audio. The encoded blocks have to be encapsulated in a suitable protocol for transport, eg. RTP.

It is one of the codecs used by AIM Triton, the Gizmo5, QQ, and Google Talk. It was formerly a proprietary codec licensed by Global IP Solutions. As of June 2011, it is part of open source WebRTC project, which includes a royalty-free license for iSAC when using the WebRTC codebase.