Talk:G.711

Talk
I don't understand that compressed s0000000wxyza... uncompressed s000wxyz part at all. Maybe someone can explain it? Thanks, --Abdull 18:23, 4 Apr 2005 (UTC)
 * I have added a couple of examples which I hope make it clearer. Alf Boggis (talk) 08:46, 24 October 2005 (UTC)

G711 also samples at 24KHz???
I am looking at a streaming product on www.barix.com and the manual for their "Instreamer" says that it can stream G711 at 8 AND 24KHz however there is no mention that this codec is capable of doing that in this article?? Could someone who is technical explain and possibly edit the article with this extra information. —Preceding unsigned comment added by 165.228.113.73 (talk) 03:19, 7 March 2008 (UTC)

On 23rd October 2005, user 212.56.108.219 added the following to the article:

From memory ( The detail could well be wrong ) A law compresses Linear value 4096 to 127 XOR 0x55 Linear value 0 to 0 XOR 0x55 Linear value -4096 to -128 XOR 0x55

u - law compresses Linear value 8197 to 0x01 Linear value 0 to 0x7F Linear value -0 to 0x80 Linear value -8197 to 0xFF

The 'zero' for A - law is 0 XOR 0x55. The 'zero' for u - law is + 127

I think it would be good to include this, but I don't have time to check at the moment so I have put it here for the record. Alf Boggis (talk) 08:39, 24 October 2005 (UTC)

Silent A-law
Hi,

I have been looking into the G.711/G.726 recommendations, and it seem to me that a silent soundstream (PCM data of value zero) should result in the A-law encoded codewords of 0xD5, not 0x55.

Regards, Jacob

The text tell there is a 0.125ms algorithmic delay. This is not true : if the decoding is done in hardware the Bytes are decoded on the fly

There is no algorithmic delay, Laurent.


 * 0x55 is negative 0, 0xd5 is positive 0. You may pick one to be the real zero, but I don't think G.711 specifies which. Carewolf (talk) 09:01, 1 December 2009 (UTC)

Total cock-up of sign bit
The sign bit simply doesn't work this way in signed PCM. The examples are only valid for s = 0. For s = 1 there are 1s following which are removed, not zeroes.

Laurent is right - there is zero algorithmic delay.

And there is also no widely-accepted convention on bit numbering. IBM number 128 as bit 0 and 1 as bit 7. This is *why* the ITU define a convention. —Preceding unsigned comment added by 213.123.226.227 (talk) 23:09, 17 June 2009 (UTC)


 * It is worse than that but gets difficult to explain in the text. G.711 uses sign=1 as positive and sign=0 as negative unlike normal 2-compliment numbers. So a ordinary negative number is converted like this: if v<0 then s=0; v=1-v else s=0x80; v=v; Carewolf (talk) 09:05, 1 December 2009 (UTC)

A-law simplicity
The article states that A-law is easier to compute than μ-Law. There is nothing in the main A-law or μ-Law articles to support that statement. Shouldn't this be moved to the A-law article? Same goes for the algorithm for computing each codec that Alf Boggis talks about above. Dinjiin (talk) —Preceding undated comment added 20:47, 5 August 2011 (UTC).

A-law is easier to compute than mu-law. The difference is not big anymore compared to so many other encodings. One of the problems is that mu-law does not encode a full binary spectrum, (it encodes more than 13bit but not fully 14bit), that makes it more expensive to encode to and from since all other encodings encode a binary spectrum. For instance to convert from 16bit to 13bit (for a-law) is shifting 3bit, but to convert to (-8160-8159) mu-law is to shift 2bit and then subtract a shift by 8 bit and add a shift by 12bit, if I remember correctly. Carewolf (talk) 15:06, 16 August 2011 (UTC)

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