Cisco TelePresence MCU 4200 Series

Audio distorted using G.722.1 Annex C

Why is my audio distorted when using G.722.1 Annex C?

This article applies to the following products:

  • Cisco TelePresence IP GW 3500 / MSE IPGW blade
  • Cisco TelePresence IP VCR 2200 / MSE VCR blade
  • Cisco TelePresence ISDN GW 3200 and 3241 / MSE 8310 and 8321 ISDN blades
  • Cisco TelePresence MCU 4200 Series
  • Cisco TelePresence MCU 4500 Series
  • Cisco TelePresence MCU 5300 Series
  • Cisco TelePresence MCU MSE Series
  • Cisco TelePresence Serial GW 3340 / MSE 8330 blade

The ITU specification for G.722.1 Annex C states that the RTP timestamp clock should be 32KHz and there should be a particular byte order. Many endpoints will use an 8KHz timestamp clock and/or a swapped byte order, creating four possible options:

  • 32KHz RTP clock, ITU byte order (ITU spec)
  • 32KHz RTP clock, swapped byte order
  • 8KHz RTP clock, ITU byte order
  • 8KHz RTP clock, swapped byte order

Cisco acquired TANDBERG/Codian products have a database of endpoints and software revisions for these endpoints so that the correct option of G.722.1C sent to each endpoint is what it will decode, and to allow the Cisco acquired Codian unit to correctly decode the audio. If an endpoint is not in the database, or is using an unknown software revision, then the wrong flavor of G.722.1C may be sent. This can cause the audio to sound distorted or occasionally can become completely inaudible.

In the event of a problem with G.722.1C, Cisco TelePresence recommends that you upgrade to the latest software version available for your Cisco acquired TANDBERG/Codian unit. This will have the most up-to-date interoperability table. If problems persist, try disabling G.722.1C on your unit and contact Cisco customer support.

January 22nd, 2013 TAA_KB_123