internet Speech Audio Codec

Internet Speech Audio Codec ( iSAC ) is an open documented, royalty- free wideband speech codec, originally developed by Global IP Solutions ( GIPS). It is suitable for IP telephony applications and streaming audio. The encoded blocks have to be packaged for transfer to a suitable protocol, such as RTP.

In contrast to this iLBC codec was proprietary, that is, the implementation must be licensed gypsum and the algorithm was not available. As a result of the acquisition of GIPS by Google Inc., the method is free of license fees for unconditional use available to everyone and the reference implementation is distributed as free software under the terms of a BSD-style license.

It is used in Gizmo5, Google Talk, and possibly soon in Microsoft products (MSN and Microsoft Office Real-Time Collaboration RTC). Previously it was used in Skype.

ISAC is a wideband codec with variable bit rate, can adapt its bit rate 10-32 kbit / s.

Parameters and characteristics

  • Sampling frequency of 16 kHz
  • Variable bit rate adaptable packet size ( 10 to 32 kbit / s or 30 to 60 milliseconds)
  • Complexity comparable to G.722.2 at comparable bit rates
  • Delay in the proceedings are: packet size plus 3 milliseconds
Real-Time Transport Protocol BSD licenses Sampling rate Bitrate
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