----- Original Message ----- From: "Michael L. Williams" To: Sent: Saturday, July 27, 2002 1:38 PM Subject: Re: polycom Video Unit [7:49882]
> "John Neiberger" wrote in message > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > I suppose it depends on the unit but ours mainly use unicast to the Cisco > > MCU. As far as I know they use standard H.323. The downside if you're > > using an MCU is that the PolyComm units have a lot of different codecs > > available that might not be known by the MCU. For example, the Cisco MCU > > can only do G.711 audio, but if you let two video units speak directly to > > each other they use G.726 ( I think. Maybe it's G.722?) and it sounds > much > > better. > > That brings up an interesting question tho.... unless the MCU is converting > between codecs for end stations that might want to use different codecs, > must the MCU "understand" the codec or would it simply act as a relay > startion for that data..... (i.e. if two end-stations are using a codec > that they understand but the MCU doesn't, would it be a problem since the > MCU would merely forward the "unknown" (to it) audio data to the other end > station). > > The Cisco MCU supports many more codecs than G.711 including the popular > G.729 codec (which gives roughly G.711 quality with an 8:1 compression). > The G.722 (you were right.. it's G.722, not G.726) that covers from > 50-6900Hz instead of 50-3900Hz as most narrowband codecs do. So if you're > trying to play more high fidelity sound, you may want to use that. I > haven't seen many units that support this codec though (but I have by no > means seen tons of units, just a few). However, if the audio you're > trasmitting is human speech, the G.722 isn't going to gain you much in terms > of sound quality since it would be preserving an additional frequency range > that's not used alot by human speech. > > Does anyone have any input or experience with how and/or when the MCU codec > support comes into play? I would think that if the endpoints are at the > same datarate and using the same audio/video codecs, the MCU would just be a > bounce point and the actual codecs in the MCU wouldn't be utilized.... Just > a theory tho.. > > Mike W. > > > You pose a good question about the MCU. I'm not very experienced with H.323, gatekeepers, and such so I can't answer that. I know just enough to be hazardous. Regarding the G.722, it sounds noticably better than G.711, as witnessed by a couple of senior Cisco engineers who wanted to witness that (plus a few other issues) for themselves. They swore that G.711 should sound just fine, but compared to G.722 it sounds like someone placed a pillow over the speaker and it's more difficult to distinguish certain syllables. John Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=49983&t=49882 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
