Avaya Audio Quality Terminology User Manual download pdf (Page 2)

1 Introduction

This document defines a variety of terms used to describe voice-related artifacts experienced in

telephony. It is expected that this terminology will be used primarily by Avaya business partners

and Avaya Global Services teams to facilitate the interpretation and understanding of voice-

related problems experienced in the field.

2 Audio processing components and terminology

In a typical telephony call, speech from talker to listener often passes through the following

processing components and in the order identified in Figure 1.

Expander

(noise

reduction)

Speech

encode

Speech

decode

Packet-loss

conealment

Automatic

Gain

control

network

Echo

controller

Echo

controller

mic

speaker

echo

path

reverse of below

Figure 1. Components of the end-to-end speech path. The upper path is

identical to the lower path, but reversed in order. The network could be

TDM, packet (VoIP), or a combination of the two.

The talker’s voice enters at the microphone on the left side of Figure 1, then to the microphone

expander, voice coder, network transport, voice decoder, packet-loss concealment, echo

controller, automatic gain control and, finally, the listener’s ear.

2.1 Audio Processing Components

2.1.1 Echo controller: broad term meaning an echo canceler, echo suppressor, or a

combination of the two. Speakerphone algorithms are also included. An echo controller

prevents a talker from hearing distant reflections (echoes) of his/her own voice,

reflections caused by acoustic or electrical reflection points within the telephone network

and end-user equipment. Echo controllers are often only partially successful, and this is

why echo is sometimes heard even though the call path is known to include echo

controllers. Often, people use the term “echo canceler” when in fact what is being

referred to is an echo controller.

2.1.2 Echo canceller: a software or hardware implementation of a digital signal processing

algorithm designed to model and subtract-out – or cancel – the reflection, or echo, of a

speech signal. Strictly speaking, an echo canceler does not introduce attenuation or

suppression into the speech paths to reduce the loudness of echo. The term canceler

refers to an adaptive digital filter that models the physical echo path and subtracts that

(excited) model from the return speech path.

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Avaya Audio Quality Terminology User Manual Page 2

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