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

Introduction

This article relates to the Cisco TelePresence MCU 4203, Cisco TelePresence MCU MSE 8420, Cisco TelePresence IP VCR 2210, Cisco TelePresence VCR MSE 8220, Cisco TelePresence ISDN GW 3241, Cisco TelePresence ISDN GW MSE 8321, Cisco TelePresence IP GW 3510, Cisco TelePresence MCU 4505 and Cisco TelePresence MCU MSE 8510 products.

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

A. 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

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 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, TANDBERG recommends that you upgrade to the latest software version available for your 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 TANDBERG customer support.

Related Information

• Technical Support & Documentation - Cisco Systems