Codecs: Difference between revisions
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<google>ENGELSK</google> | |||
==General== | ==General== | ||
* [http://en.wikipedia.org/wiki/List_of_codecs List of codecs - Wikipedia, the free encyclopedia] | * [http://en.wikipedia.org/wiki/List_of_codecs List of codecs - Wikipedia, the free encyclopedia] | ||
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* [http://www.itu.int/rec/T-REC-G.729/e G.729 : Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP)] | * [http://www.itu.int/rec/T-REC-G.729/e G.729 : Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP)] | ||
* [http://en.wikipedia.org/wiki/List_of_codecs List of codecs - Wikipedia] | |||
* [http://en.wikipedia.org/wiki/G.711 G.711 - Wikikpedia] | |||
==Documents from ITU== | |||
* [http://www.itu.int/rec/T-REC-G.711/e 3 documents G.711 : Pulse code modulation (PCM) of voice frequencies] | |||
* [http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.711-198811-I!!PDF-E&type=items ITU-T Recommendation G.711] - (STD.ITU-T RECMN G.711-ENGL 1989) | |||
5 Relationship between the encoding laws and the audio level | |||
The relationship between the encoding laws of Tables 1/G.711 and 2/G.711 and the audio signal level is | |||
defined as follows: | |||
A sine-wave signal of 1 kHz at a nominal level of 0 dBm0 should be present at any voice frequency output of | |||
the PCM multiplex when the periodic sequence of character signals of Table 5/G.711 for the A-law and of | |||
Table 6/G.711 for the m-law is applied to the decoder input. | |||
The resulting theoretical load capacity (Tmax) is +3.14 dBm0 for the A-law, and +3.17 dBm0 for the m-law. | |||
Note - The use of another digital periodic sequence representing a nominal reference frequency of 1020 Hz at | |||
a nominal level of -10 dBm0 (preferred value, see Recommendation O.6) or 0 dBm0 is acceptable, provided that the | |||
theoretical accuracy of that sequence does not differ by more than ± 0.03 dB from a level of -10 dBm0 or 0 dBm0 | |||
respectively. In accordance with Recommendation O.6, the specified frequency tolerance should be 1020 Hz + 2 Hz, | |||
-7 Hz. | |||
If a sequence representing -10 dBm0 is used, the nominal value at the voice frequency outputs should be | |||
-10 dBm0. | |||
* [http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.711-199909-I!AppI!PDF-E&type=items A high quality low-complexity algorithm for packet loss concealment with G.711] | |||
* [http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.711-200002-I!AppII!PDF-E&type=items A comfort noise payload definition for ITU-T G.711 use in packet-based multimedia communication systems] | |||
==Links about Paket sizes and framrates== | |||
Søg f.exk på: g.711 20ms | |||
eller: Packetization g.711 160 80 | |||
eller:g711 framerate | |||
* [http://www.informit.com/articles/article.aspx?p=357102 InformIT: Quality of Service Design Overview > QoS Requirements of VoIP] | |||
* [http://wiki.forum.nokia.com/index.php/KIS000796_-_Frame_length_variation_for_G.711_encoder KIS000796 - Frame length variation for G.711 encoder - Forum Nokia Wiki] | |||
* [http://www.newport-networks.com/cust-docs/52-VoIP-Bandwidth.pdf Newport Networks VoIP Bandwidth Calculation] | |||
* [http://www.tijdhof.com/technotes/tech_faq_codec.pdf GRANDSTREAM NETWORKS FAQ – CODEC] | |||
* [http://msdn.microsoft.com/en-us/library/bb821744.aspx Standards and Drafts for RTC] | |||
* [http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=869713&SiteID=1 Recording and Playing back streaming sound in C# on Motorola Q Smartphone] | |||
* [http://msdn.microsoft.com/en-us/library/ms811371.aspx BufferPositionNotify Structure (Microsoft.DirectX.DirectSound)] | |||
<google>ENGELSK</google> | <google>ENGELSK</google> | ||
Revision as of 05:35, 20 May 2008
<google>ENGELSK</google>
General
Audio codecs
- Download Open Source G.729 (g729) and G.723.1 (g723) diff codec_g729 codec_g729a codec_g723 for Asterisk Linux
- ITU G.729 - voip-info.org
- Free G729 Acm Codec Diver - Plugin codec for RTC Sip softphone
- G.729 : Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP)
Documents from ITU
- 3 documents G.711 : Pulse code modulation (PCM) of voice frequencies
- ITU-T Recommendation G.711 - (STD.ITU-T RECMN G.711-ENGL 1989)
5 Relationship between the encoding laws and the audio level The relationship between the encoding laws of Tables 1/G.711 and 2/G.711 and the audio signal level is defined as follows: A sine-wave signal of 1 kHz at a nominal level of 0 dBm0 should be present at any voice frequency output of the PCM multiplex when the periodic sequence of character signals of Table 5/G.711 for the A-law and of Table 6/G.711 for the m-law is applied to the decoder input. The resulting theoretical load capacity (Tmax) is +3.14 dBm0 for the A-law, and +3.17 dBm0 for the m-law. Note - The use of another digital periodic sequence representing a nominal reference frequency of 1020 Hz at a nominal level of -10 dBm0 (preferred value, see Recommendation O.6) or 0 dBm0 is acceptable, provided that the theoretical accuracy of that sequence does not differ by more than ± 0.03 dB from a level of -10 dBm0 or 0 dBm0 respectively. In accordance with Recommendation O.6, the specified frequency tolerance should be 1020 Hz + 2 Hz, -7 Hz. If a sequence representing -10 dBm0 is used, the nominal value at the voice frequency outputs should be -10 dBm0.
- A high quality low-complexity algorithm for packet loss concealment with G.711
- A comfort noise payload definition for ITU-T G.711 use in packet-based multimedia communication systems
Links about Paket sizes and framrates
Søg f.exk på: g.711 20ms eller: Packetization g.711 160 80 eller:g711 framerate
- InformIT: Quality of Service Design Overview > QoS Requirements of VoIP
- KIS000796 - Frame length variation for G.711 encoder - Forum Nokia Wiki
- Newport Networks VoIP Bandwidth Calculation
- GRANDSTREAM NETWORKS FAQ – CODEC
- Standards and Drafts for RTC
- Recording and Playing back streaming sound in C# on Motorola Q Smartphone
<google>ENGELSK</google>