Avaya Audio Quality Terminology User Manual

Audio Quality Terminology

ABSTRACT

The terms described herein relate to audio quality artifacts. The intent of this document is to ensure Avaya customers, business partners and services teams engage in effective communication involving audio quality related issues.

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 voicerelated 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.

speaker

mic

Echo

controller

Expander

(noise

reduction)

Speech

encode

reverse of below

network

Speech decode

Packet-loss conealment

Automatic

Gain

control

Echo

controller

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.

echo

path

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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