Scaling Studies of Perceived Source Width Juha Merimaa Institut für Kommunikationsakustik...

Binaural and Spatial Hearing Group

Scaling Studies of Perceived Source Width

Juha Merimaa

Institut für KommunikationsakustikRuhr-Universität Bochum

Binaural and Spatial Hearing Group

Outline

• Introduction• Background on listening tests• Description of the conducted pilot test• Analysis methods & preliminary results• Discussion & summary

Binaural and Spatial Hearing Group

Introduction

• A room or a hall broadens the perceived width of auditory objects

• Traditionally auditory source width (ASW) has been investigated as a descriptor for concert halls

• How does the broadening depend on source signals?

Binaural and Spatial Hearing Group

In other words...

• In a scene based paradigm– source broadening is due to the part of room

effect that is grouped with source signals– the rest of room effect is resolved into a

separate percept

• What are the spatial features related to auditory “deconvolution” of reverberation

Binaural and Spatial Hearing Group

Listening test basics

• Quantifying auditory perception• Levels of measurement

Interval

OrdinalNominal

Ratio

Short Long 1 2 3

1 2 30 41 2 30 4

Binaural and Spatial Hearing Group

Possible test methods for assessing ASW

• Direct scaling– Rating– Rank ordering– Assigning stimuli in successive categories

• Constant reference– All stimuli are judged relative to a single

reference stimulus

Binaural and Spatial Hearing Group

Possible test methods (contd.)

• Method of adjustment– Listeners adjust a variable reference to

correspond to each stimulus

• Adaptive procedures– Reference is adaptively adjusted based on

listeners judgements

• Pairwise comparisons– Each stimulus is judged relative to all others

Binaural and Spatial Hearing Group

Why pairwise comparisons?

• Source broadening is expected to be a sum of several interaural signal features

• All except pairwise comparison methods force the results onto a linear scale– Weighting of dimensions implicit in the data• Can be accessed with factor analysis

– Weights may vary between individuals, which will result in noisy unidimensional data

Binaural and Spatial Hearing Group

Pilot listening test• Gathering both preference and distance

data between pairs

Binaural and Spatial Hearing Group

Stimuli

– Speech (sp)

– Cello, f0 = 196 Hz

(ce)– Snare drum (sn)

– Two harmonic complexes,f0 = 196 Hz, -12 dB/oct• No modulation (h1)• Freq. mod. 1%, 6 Hz (h2)

– Pink noise 100 Hz –10 kHz (ns)

• Anechoic samples convolved with binaural room responses

Binaural and Spatial Hearing Group

Binaural room responses

• Diffuse field and system compensated responses– Medium size diffuse concert hall (p)• RT = 2.2 s, 1-IACC

E3 = 0.78

– Large multipurpose hall (a)• RT = 2.4 s, 1-IACC

E3 = 0.02

– Small listening room (s)• RT = 0.5 s, 1-IACC

E3 = 0.32

Binaural and Spatial Hearing Group

Altogether 18 stimuli resulting in 153 permutations

Binaural and Spatial Hearing Group

Analysis of preference data

• A single run comparing all the the pairs results in a preference matrix that can be used to rank order the stimuli

• In an ideal case each run will yield the same perfectly ordered set of data

A B C DAB 1C 0 0D 1 1 1

Binaural and Spatial Hearing Group

Real world comparative judgements

• Each stimulus has a dispersion on a psychological scale

• Each judgment of distance and order depend on current points of perception

Binaural and Spatial Hearing Group

Checking for consistency

• Circular triads• Mean for random answers

with 18 stimuli: 204• Average in collected data approx. 40• All data matrices consistent with

significance p < 0.01

A B

C

Binaural and Spatial Hearing Group

Unidimensional scaling

• Simplest scaling method: count the number of times a single stimulus is prefered over all others

Binaural and Spatial Hearing Group

Wincount statistics, CR = 60

0 20 40 60 80 100 120 140

s_h1s_h2a_h1a_sns_sna_h2s_cea_cea_nsa_sps_sps_nsp_snp_cep_h1p_spp_h2p_ns

Binaural and Spatial Hearing Group

Comparison with stimulus IACC

0 20 40 60 80 100 120 140

s_h1s_h2a_h1a_sns_sna_h2s_cea_cea_nsa_sps_sps_nsp_snp_cep_h1p_spp_h2p_ns

Wincount

0 0.15 0.3 0.45 0.6 0.75 0.9 1.051-IACC

3

Binaural and Spatial Hearing Group

More sophisticated scaling

• Thurstone's law provides a method for mapping pair comparison data on an interval scale– Assumes normally distributed

unidimensional data– Includes tests for checking the fit

• Results– Significance of deviation from data p < 0.01

Binaural and Spatial Hearing Group

Multidimensional scaling

• Uses distances between stimuli to construct a spatial representation ofdata in n dimensions

• Metric (interval) and nonmetric (ordinal) procedures

• Few assumptions on data• Works well with a relatively small number

of test subjects

Binaural and Spatial Hearing Group

-2-1

01

23 -2

0

2-1.5

-1

-0.5

0

0.5

1

1.5

p_ns

p_sp

p_h1

p_h2

p_ce p_sn

s_sp

s_ns

a_ns

a_sp

a_sn a_h2

a_ce

s_sn s_ce

s_h2

s_h1

a_h1

3-D scaling of all stimuli

Binaural and Spatial Hearing Group

Comparison of the large halls

-2 -1 0 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

a_ce

a_h1 a_h2

a_ns

a_sn

a_sp

p_ce p_h1

p_h2

p_ns

p_sn

p_sp

Binaural and Spatial Hearing Group

Multipurpose hall vs. Listening room

-2 -1 0 1-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

a_ce

a_h1

a_h2

a_ns

a_sn

a_sp

s_ce

s_h1

s_h2

s_ns

s_sn

s_sp

Binaural and Spatial Hearing Group

Concert hall vs. Listening room

-2 -1 0 1 2 -2

0

2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

p_h1 p_h2

p_ns

p_sp

p_ce

p_sn

s_ns

s_sp

s_sn

s_ce s_h2

s_h1

Binaural and Spatial Hearing Group

Discussion & conclusions

• The perception of auditory source width is clearly multidimensional– Results between the most similar spaces

suggest separate source and room dimensions with some interaction

– Euclidian metric of MDS might not reflect human perception between extreme cases

• The pilot data is insufficient to draw more firm conclusions

Binaural and Spatial Hearing Group

Future work

• A larger listening test with a reduced set of stimuli

• Interpreting the dimensions in terms of binaural cues– Breaking the experiment into several

unidimensional studies– Use gained results in choosing stimuli

• Similar investigations into envelopment