【資料名稱】：TFO FOR AMR

【資料作者】：NSN

【資料日期】：2010

【資料語言】：英文

【資料格式】：PDF

【資料目錄和簡(jiǎn)介】：

Wideband AMR requires end to end tandem free operation support. If TFO were not
supported, the transcoder would need to downsample the audio signal according to
G.711, where the audio frequency range is restricted to 300 - 3400 Hz. This would invalidate
the sound quality improvements introduced by wideband AMR. However, e.g. for
inter-PLMN wideband AMR calls, the transport chain must be ensured to be transparent
in order to carry TFO.
The codec mode selected can be restricted by the radio conditions in order to achieve
optimal audio performance. It can be changed every 40 ms. The codec includes a
source-controlled rate adaptation mechanism, which allows speech to be encoded at a
lower average rate, by taking speech inactivity into account.