Hi All, Can someone explain to me the difference between g711's ulaw and alaw codecs? Is it just different header info or is the actual payload in each encoded differently? I have thus far noe been able to find any difinative information onthe matter. All I've managed to find out that they are "similar", they sound the same and that it doesn't matter which you use. Could someone knowledgable please enlightmen me?
Partly is is down to the fact that G.711u (mu-law) is primarily used in the USA and G.711a (a-law) is used in Europe. Like you, I am not sure if the exact differences - they have the same bitrate and audio, although there are minor differences in the format. Peter -----Original Message----- From: Eric Bishop [mailto:asterisk.eric@gmail.com] Sent: 16 December 2004 10:56 To: Asterisk Users Mailing List - Non-Commercial Discussion Subject: [Asterisk-Users] g711 ulaw vs alaw Hi All, Can someone explain to me the difference between g711's ulaw and alaw codecs? Is it just different header info or is the actual payload in each encoded differently? I have thus far noe been able to find any difinative information onthe matter. All I've managed to find out that they are "similar", they sound the same and that it doesn't matter which you use. Could someone knowledgable please enlightmen me? _______________________________________________ Asterisk-Users mailing list Asterisk-Users@lists.digium.com http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Thank you.
Whisker, Peter schrieb:> Partly is is down to the fact that G.711u (mu-law) is primarily used in the > USA and G.711a (a-law) is used in Europe. > > Like you, I am not sure if the exact differences - they have the same > bitrate and audio, although there are minor differences in the format. >Hi, it is just a small difference in how to interpret one bit (signed value vs. unsigned value with offset). Roger.
> it is just a small difference in how to interpret > one bit (signed value vs. unsigned value with offset).Which one is signed?
On Thu, 16 Dec 2004, Roger Schreiter wrote:> Whisker, Peter schrieb: > > Partly is is down to the fact that G.711u (mu-law) is primarily used in the > > USA and G.711a (a-law) is used in Europe. > > > > Like you, I am not sure if the exact differences - they have the same > > bitrate and audio, although there are minor differences in the format. > > > it is just a small difference in how to interpret > one bit (signed value vs. unsigned value with offset).I think there is a bit more difference. The byte code of ulaw is a monotonic function of the amplitude whereas in alaw the code is xor:ed with a bit mask of 0x55. Also, the quatization function is different, though the same general idea is used. If the difference is important to you you should read the standard itself. Peter
> I think there is a bit more difference. The byte code of ulaw is a > monotonic function of the amplitude whereas in alaw the code is xor:ed > with a bit mask of 0x55.Wow! Encryption!
On Thu, 16 Dec 2004, Roy Sigurd Karlsbakk wrote:> > I think there is a bit more difference. The byte code of ulaw is a > > monotonic function of the amplitude whereas in alaw the code is xor:ed > > with a bit mask of 0x55. > > Wow! Encryption!I think it is done to keep the number of 1 and 0 on the line roughly equal. For some links this was/is desireable. Peter
On Thu, Dec 16, 2004 at 01:11:34PM +0100, Roy Sigurd Karlsbakk spake thusly:> >I think there is a bit more difference. The byte code of ulaw is a > >monotonic function of the amplitude whereas in alaw the code is xor:ed > >with a bit mask of 0x55. > > Wow! Encryption!Scary thing is, it would be illegal under DMCA to un-XOR it! (In the US anyway) -- Tracy Reed http://copilotcom.com This message is cryptographically signed for your protection. Info: http://copilotconsulting.com/sig -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 189 bytes Desc: not available Url : http://lists.digium.com/pipermail/asterisk-users/attachments/20041218/6d76c79a/attachment.pgp
Tracy R Reed wrote:>On Thu, Dec 16, 2004 at 01:11:34PM +0100, Roy Sigurd Karlsbakk spake thusly: > > >>>I think there is a bit more difference. The byte code of ulaw is a >>>monotonic function of the amplitude whereas in alaw the code is xor:ed >>>with a bit mask of 0x55. >>> >>> >>Wow! Encryption! >> >> > >Scary thing is, it would be illegal under DMCA to un-XOR it! (In the US anyway) > >Amusing, but offtopic, incorrect, and misleading...
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