A Methodology for Deriving VoIP Equipment Impairment Factors for a Mixed NB/WB Context

Wireless Access ResearchAdil Raja August 2007

A Methodology for Deriving VoIP Equipment Impairment Factors for a

Mixed NB/WB Context

Adil Raja13th August, 2007

Wednesday 14 November 2012


VoIP- The Shift to WB Paradigm

• The NB and WB would have to coexist for some time. i.e. operate either in cascade or in parallel.

• This work proposes an extension to E-Model for the parallel case.



The E-Model

• An Instrumental Model initially designed for NB handset telephony.

• R= R0-Is-Id-Ie,eff+A• R0=93.2 – the basic SNR.• Is - simultaneous impairments e.g. OLR, non-

optimum sidetone.• Id - e.g e2e delay and echo.• Ie,eff Impairments due to low-bitrate codecs and

packet loss.• A – Advantage factor.



The E-Model…

• R <-> MOS



Moller’s WB extension to E-Model

• Consider Two experiments• Each experiment is composed of two sets of speech

samples.• MOS evaluation is done based on ACR paradigm.• One set is evaluated in the NB/WB context.• The other set is evaluated in the NB context, by

downsampling the WB coded speech samples.



Example



ExampleSTUDY GROUP 12 – DELAYED CONTRIBUTION 46

Discussion on unified objective methodologies for the comparison of voice quality of narrowband and wideband scenarios



The Extension

• Rnb=a+(eRnb/wb/b-1)• a=169.38• b=176.32• The R-scale is stretched by 29%• A linear extension with somewhat similar

results exists.



R-scale extension with PESQ

• Two sets of speech samples are created.• Both contain stimuli coded by NB and WB

codecs. (124 samples each).• The first (NB/WB) set is evaluated using

PESQ-WB.• The NB coded stimuli were upsampled to

16 kHz.



R-scale extension with PESQ

• How to evaluate the 2nd part of the test?• For the 2nd (NB) part of test three options

were considered for evaluating the samples.

• In Option 1 All the files (ref|deg of NB|WB) were downsampled to 8 kHz.

• This qualifies as a NB test.



R-scale extension … Option 1RNB=a+b*RNB/WB

Max RNB=100.48

Suggests no extension.



The outcome



R-scale extension … Option 2

All Evaluation is done by PESQ-WB.

Contracts the scale instead.



R-scale extension … Option 3

• Same as Option 2 but the Ref samples for NB stimuli are downsampled/upsampled.

• This would clearly tantamount to repeating option 1 but with PESQ-WB



An AlternativeUsing Supp 23 Exp 1&3.

Mapping between PESQ-WB & -NB evaluted NB coded samples.

Max RNB=107.1786



The Codecs

• G.729• AMR-NB – 7.4 & 12.2 kbps• G.723.1 – 6.3 kbps• G.722.1 24/32 kbps• G.722.2 – all 9 modes



Other metrics• MLR - [0,2.5,. . . , 15, 20, . . . , 40]%• CLP - 10, 50, 60, 70 and 80%. • PI – 10-60 ms.• A total of 2,820 conditions were simulated• A given condition was applied to a file for 30 times; to

negate the effect of loss location.• Thus a total of 3,38,400 speech files were created.• Evaluation was done on beowulf using PESQ-WB



Ie,wb,eff vs various codecs



Scatter plot –training data



Scatter plot-Testing data



Surface plots of the derived functions



Parameter Significance



Ie,wb,eff vs mlr and mbl



Ie,wb,eff vs mlr and PI


Engineering

A Methodology for Deriving VoIP Equipment Impairment Factors for a Mixed NB/WB Context