Jan Reimes

HEAD acoustics GmbH

Sophia Antipolis, 2017-05-10

Loudness of transmitted speech signals for

SWB and FB applications

Challenges, auditory evaluation and proposals for

handset and hands-free scenarios

Loudness of Transmitted Speech SignalsJan Reimes 2

Introduction (1/2)

▪ Loudness of received speech signal - most simple but important

quality parameter of a communication device!

▪ Too loud: annoying, may cause hearing damage!

▪ Too quiet: impact on intelligibility (and other aspects of

conversational quality…)

▪ Several measurement standards provide requirements for

comfortable listening level

▪ Loudness == Level? Psycho-acoustics!

Loudness of Transmitted Speech SignalsJan Reimes 3

▪ For NB and WB terminals, so-called loudness ratings (LR) are used

to evaluate transmission characteristics (e.g. ITU-T P.79)

▪ Basic concept of LR: calculate attenuation (in dB) to achieve same

perceived loudness compared to intermediate reference system (IRS)

▪ Weighted sum of transfer function provides attenuation versus IRS

▪ Technical measure; no information about absolute loudness

▪ Addresses mainly linear distortions

▪ Method not (yet?) defined for SWB/FB applications

L/d

B

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15

f/Hz300 500 2000 4000

Reference System 𝑹 𝒇L

/dB

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f/Hz300 500 2000 4000

Introduction (2/2)

L/d

B

5

7

9

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f/Hz300 500 2000 4000

Device under test 𝑯 𝒇

𝑳𝑹 ~

𝒇

𝒘 𝒇 ⋅ 𝑫 𝒇

𝑫(𝒇) = 𝑯 𝒇 − 𝑹 𝒇

Loudness of Transmitted Speech SignalsJan Reimes 4

▪ Standardization: ITU-T SG12 / Q5 launched new work item

“P.Loudness”

▪ Goal: evaluate and/or modify existing loudness models originated

from psycho-acoustic domain

▪ Several standardized models already exists:

▪ “Zwicker approach” (DIN 45631/A1, ISO 532-1)

▪ “Moore/Glasberg approach” (ANSI S3.4-2007, ISO 532-2)

▪ Current “release candidate model” for P.Loudness available

▪ Based on very basic auditory experiments, no real terminals

▪ Loudness model is based on stationary loudness (ANSI S3.4)

▪ Modifications are fitted to auditory results

▪ Two modes for handset/hands-free are required

▪ Not applicable on artificial head recordings (handset)

▪ No binaural aspects considered

Recent work on loudness

Loudness of Transmitted Speech SignalsJan Reimes 5

▪ Large test corpus based on binaural recordings of terminals (3G,

4G, VoIP) and realistic simulations (compression, codecs,

loudspeaker distortions)

▪ 8 German test sentences (ITU-T P.501) as source material

▪ Bandwidth from NB (up to 3.4 kHz) to FB (up to 20 kHz)

▪ Level range between 40 and 90 dBSPL

52 conditions per mode (handset and hands-free mode)

4 sentences each

208 test stimuli per mode

Auditory evaluation (1/3)

Stimulus

Binaural recording

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▪ Absolute / categorial loudness assessment on 25-point scale

▪ 7 anchor definitions for better orientation

▪ Already used in previous studies

▪ 20 normal-hearing test subjects per mode

▪ Hearing-adequate playback of

binaural recordings in listening lab

Auditory evaluation (2/3)

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▪ Prior to evaluation: determination of individual loudness functions per

test subject with a reference sound

▪ Principle of reference sound: should cause similar “loudness

excitation” as speech, but independent of language, content, talker, …

▪ Three different reference sounds were evaluated:

▪ 1 kHz Sine tone (refers to definition of sone/phon)

▪ 1 Bark noise at 1 kHz (used in initial P.Loudness experiments)

▪ 3 Bark noise at 1 kHz (less tonal, “smooth”)

Auditory evaluation (3/3)

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▪ Several state-of-the-art loudness models are evaluated:

▪ Zwicker: ISO 532-1

▪ Moore/Glasberg: ANSI S3.4 (stationary), version 2002 & 2016,

LT/ST smoothing

▪ P.Loudness candidate (stationary)

▪ Non-stationary models provide loudness vs. time curve, several

single value calculations are possible:

▪ Average

▪ N5 percentile (peak-oriented)

▪ LL(p) (used in recent work)

▪ Auditory results of test stimuli provide

values on point-scale

Comparison to loudness models?

Results of loudness models (1/5)

Loudness of Transmitted Speech SignalsJan Reimes 9

▪ Proposed procedure for comparison between loudness models

(results in phon/sone) and auditory test results (in points)

▪ Select reference signal (Sine, 1 Bark noise, 3 Bark noise, …)

▪ Calculate inverse of loudness functions with mapping function

▪ Transform auditory results in points to level in dBERL

▪ Example: 15.0 point in listening test refers to ≈75 dBERL

(same loudness as 3 Bark noise reference signal at 75 dBSPL)

Results of loudness models (2/5)

Loudness of Transmitted Speech SignalsJan Reimes 10

▪ Proposed procedure for comparison between loudness models

(results in phon/sone) and auditory test results (in points)

▪ Select loudness model and single value aggregat

▪ Calculate loudness (in sone or phon) for selected reference

sound for a certain level range (e.g. from 40 to 90 dBSPL)

▪ Calculate mapping function between sone/phon and level

▪ Run loudness model on signal-under-test

▪ Transform output from sone/phon to level in dBERL with

previously determined mapping function

Results of loudness models (2/5)

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▪ Large amount of combinations possible (models, single values,

reference signal)

▪ Evaluation of prediction performance by RMSE*

▪ Considering uncertainty of auditory data

▪ “Baseline” performance: auditory results vs. active speech level

(ASL) acc. to ITU-T P.56 models should perform better!

Results of loudness models (3/5)

ASL/Sinus (HF)ASL/Sinus (HS)

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Results of loudness models (4/5)

Selected results per loudness model – handset mode

ISO 532-1/Avg./Sinus TVL2016-LT/Avg./3 Bark

TVL2002-ST/Avg./1 BarkP.Loudness/3 Bark

Loudness of Transmitted Speech SignalsJan Reimes 13

Results of loudness models (5/5)

Selected results per loudness model – hands-free mode

P.Loudness/3 Bark

ISO 532-1/Avg./Sinus

TVL2002-LT/N5/3 Bark

TVL2016-LT/LL(p)/3 Bark

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▪ Loudness assessment is a challenging task!

▪ SWB/FB terminals are commercially available – but currently no

instrumental loudness assessment test methods available

▪ Large auditory database and listening tests were conducted

▪ Considering state-of-the-art terminals and realistic simulations

▪ Evaluation of loudness models – no clear “winner”:

▪ ISO 532-1 very accurate for HS & HF single model for both

▪ TVL2016-LT slightly worse, but considers binaural inhibition

▪ P.Loudness candidate also performs adequately, but…

▪ New loudness model not necessarily needed?

▪ Finalize P.Loudness work item in standardization

▪ Specify application of loudness models in measurement standards

Summary & Conclusions

Jan Reimes

Research & Standardization HEAD acoustics

info@head-acoustics.de

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