Introduction
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Introduct
ion
Packet Voice Processor Commands Manual
1.4.2.1.2 Configuring for Optimal Hybrid Echo Cancellation
The Packet Voice Processor applies an adaptive filter to the Long Haul and Tail
circuits. A mathematical model of the anticipated echo is developed and subtracted
from the actual reflected echo signal. The Packet Voice Processor effectively cancels
echoes on circuits with Tail delays of up to 128ms and Echo Return Loss as severe
as 0dB.
Optimal hybrid echo cancellation depends on the Maximum Tail Delay and Echo
Return Loss (ERL) settings. When correctly provisioned, a circuit's measured
maximum reflection (Maximum Delay) never exceeds the Maximum Tail Delay
setting for the Packet Voice Processor, and the measured echo return loss is always
greater than the ERL setting. Preserving these conditions enhances the voice quality
provided to customers.
1.4.2.2 Acoustic Echo Control
Acoustic Echo Control (AEC) solves echo problems that are common in VoIP
networks due to poor acoustic isolation between the speaker and microphone of a
user’s device (e.g., handset, speakerphone, softphone). Acoustic echo becomes
more problematic with VoIP induced packet delay, making the echo more noticeable.
Ditech’s AEC feature suppresses a wide range of echo variances using algorithms
based on talker energy levels, bulk delay, and Weighted Acoustic Echo Path Loss
(WAEPL) to effectively eliminate acoustic echo and significantly improve voice
quality.
1.4.2.3 Adaptive Noise Cancellation
Ditech’s Adaptive Noise Cancellation (ANC) technology features a high-precision
noise reduction algorithm that removes background noise (such as background
noise from noisy environments) by up to 21 dB to improve the sound quality of a call,
resulting in greater customer satisfaction and enhanced call clarity. When
transcoding to more compressed codecs, ANC also reduces codec distortion.
Table 1-4 Echo Generation Delay Types
Delay Type
Description
Dispersion Delay
Dispersion Delay occurs due to bandwidth limitations and multiple
reflections.
Dispersion delay is the spreading of the signal spectral energy over time,
caused by the transmission medium's bandwidth limitations. It usually
occurs in channel banks and Voice Frequency (VF) loaded cable.
Dispersion must be included in calculations of round-trip delay, typically
ranging from 4 to 7 milliseconds, regardless of the number of channel
banks.
Approximate Propagation
Delay
Approximate propagation delay occurs due to and varies with the
transmission medium. The equipment manufacturer's specifications should
be reviewed for accurate values.
Component Delay
Component delay occurs due to transmission equipment and switching
element processing. This delay type reflects the contributions of network
components to the total round-trip delay.
