LOW LEVEL PSTN NOISE SUPPRESSION BY QUASI-COMFORT NOISE INSERTION
Original Publication Date: 1998-Jun-01
Included in the Prior Art Database: 2002-Jul-05
This publication describes a method of sup- pressing the low level noise present in the outbound audio path of a code excited linear prediction (CELP) type based digital cellular system during a subscriber to landline call. The method is a hybrid between a "straight" CELP encode and an encode using voice activity detection based comfort noise insertion. These VADKN approaches are used when transmission bandwidth is desired to be reduced during non-speech segments, while a straight encode is typically used when bandwidth is not constrained. The straight CELP encode can result in low level system (PSTN or other) back- ground noise being emphasized which, with volume amplification by the subscriber unit (SU), can result in an objectionable user perceived noise.