The Adaptive Multi-Rate (AMR or AMR-NB) audio codec is a patented audio data compression scheme optimized for speech coding. AMR was adopted as the standard speech codec by 3GPP in October 1999 and is now widely used in GSM[3] and UMTS. It uses link adaptation to select from one of eight different bit rates based on link conditions. AMR is also a file format for storing spoken audio using the AMR
codec. Many modern mobile telephone handsets can store short audio
recordings in the AMR format, and both free and proprietary programs exist (see Software support)
to convert between this and other formats, although AMR is a speech
format and is unlikely to give ideal results for other audio. The common
filename extension is UsageThe frames contain 160 samples and are 20 milliseconds long.[1] AMR uses various techniques, such as ACELP, DTX, VAD and CNG. The usage of AMR requires optimized link adaptation that selects the best codec mode to meet the local radio channel and capacity requirements. If the radio conditions are bad, source coding is reduced and channel coding is increased. This improves the quality and robustness of the network connection while sacrificing some voice clarity. In the particular case of AMR this improvement is somewhere around S/N = 4-6 dB for usable communication. The new intelligent system allows the network operator to prioritize capacity or quality per base station. There are a total of 14 modes of the AMR codec, 8 are available in a full rate channel (FR) and 6 on a half rate channel (HR).
Features
Licensing and patent issuesAMR codecs incorporate several patents of Nokia Corporation, Telefonaktiebolaget L. M. Ericsson, VoiceAge Corporation and Nippon Telegraph and Telephone Corporation.[5][6] VoiceAge Corporation is the License Administrator for the AMR and AMR-WB+ patent pools. VoiceAge also accepts submission of patents for determination of their possible essentiality to these standards.[7][8] The initial fee for professional content creation tools and "real-time channel" products is 6,500 USD. The minimum annual royalty is $10,000, which (in the first year) excludes the initial fee. Per-channel license fees fall from $0.99 to $0.50 with volume, up to a maximum of $2 million annually.[5][6] In the category of personal computer products (e.g. media players), the AMR decoder is licensed for free. The license fee for a sold encoder falls from $0.40 to $0.30 with volume, up to a maximum of $300,000 annually. The minimum annual royalty is not applied to licensed products which fall under the category of personal computer products and use only the free decoder.[5][6] More information:
Software support
from:http://en.wikipedia.org/wiki/Adaptive_Multi-Rate |