Content deleted Content added
Where are these quality evaluations reported? |
m clean up, replaced: µ → μ (2) |
||
Line 32:
The frames contain 160 samples and are 20 milliseconds long.<ref name="3gpp-26090" /> AMR uses various techniques, such as [[algebraic code excited linear prediction|ACELP]], [[discontinuous transmission|DTX]], [[voice activity detection|VAD]] and [[comfort noise|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, eight are available in a [[Full Rate|full rate channel (FR)]] and six on a [[
{| class="wikitable"
Line 67:
** The residual waveform is coded using [[algebraic code excited linear prediction]] (ACELP).
* The complexity of the algorithm is rated at 5, using a relative scale where [[G.711]] is 1 and [[G.729a]] is 15.
* [[PSQM]] testing under ideal conditions yields [[mean opinion score]]s of 4.14 for AMR (12.2 kbit/s), compared to 4.45 for [[G.711]] (
* [[PSQM]] testing under network stress yields [[mean opinion score]]s of 3.79 for AMR (12.2 kbit/s), compared to 4.13 for [[G.711]] (
== Licensing and patent issues ==
AMR codecs incorporate several [[patent]]s of [[Nokia]], [[Ericsson]], [[Nippon Telegraph and Telephone|NTT]] and VoiceAge,<ref name="voiceage-amr_licterms">{{cite web |author=VoiceAge Corporation |publisher=VoiceAge Corporation |url=http://www.voiceage.com/amr_licterms.php |title=AMR Licensing Terms |date=2007-10-14 |accessdate=2009-09-12 |archiveurl=https://web.archive.org/web/20071014162046/http://www.voiceage.com/amr_licterms.php |archivedate=2007-10-14}}</ref><ref name="voiceage-amr_licterms2">{{cite web|author=VoiceAge Corporation |publisher=VoiceAge Corporation |url=http://www.voiceage.com/amr_licterms.php |title=AMR Licensing Terms |date=June 2007 |accessdate=2009-09-12 |url-status=dead |archiveurl=https://web.archive.org/web/20071014162046/http://www.voiceage.com/amr_licterms.php |archivedate=2007-10-14 }}</ref> the last one being the ''License Administrator'' for the AMR [[patent pool]]s. VoiceAge also accepts submission of patents for determination of their possible essentiality to these standards. However, it's very difficult to determine if there were actually any patents in existence for the so-called inventions related to AMR/AMR-WB codecs, since inventors (and their lawyers) do everything they can to hide patents related to AMR/AMR-WB technology{{Citation
The initial fee for professional content creation tools and "real-time channel" products is US$6,500.{{When|date=November 2015}} 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.<ref name="voiceage-amr_licterms"/><ref name="voiceage-amr_licterms2"/>
| |||