This presentation summarises a method for the reproduction of multizone speech soundfields using perceptual weighting criteria. Psychoacoustic models are used to derive a space-time-frequency weighting function to control leakage of perceptually unimportant energy from the bright zone into the quiet zone. This is combined with a method for regulating the number of basis planewaves used in the reproduction to allow for an efficient implementation using a codebook of predetermined weights based on desired soundfield energy in the zones. The approach is capable of improving the mean squared error for reproduced speech in the bright zone by -10.5 decibels. Results also show that the approach leads to a significant reduction in the spatial error within the bright zone whilst requiring 65% less loudspeaker signal power for the case where the soundfield in this zone is in line with, and hence partially directed to, the quiet zone.

1. MULTIZONE
REPRODUCTION OF
SPEECH SOUNDFIELDS:
A PERCEPTUALLY
WEIGHTED APPROACH
Jacob Donley and Christian Ritz
School of Electrical, Computer and Telecommunications Engineering
ICT Research Institute & Global Challenges
University of Wollongong

2. 2
Room
How can we perceptually enhance
independent listening zones in a room?
Quiet Zone:
No reproduced
sound
Bright Zone:
Listening to
speech or
music
Loudspeakers
Known as Multizone Reproduction of Soundfields

3. 3
Aim: derive loudspeaker signals to
reproduce desired sound field in each zone
• Reproduced sound field modelled in the
(discrete) space (𝐱 = (𝒙, 𝒚)), time (𝑛),
frequency domain (𝑘) as:
𝑆 𝑤 𝐱, 𝑛, 𝑘 =
𝑙=1
𝐿
𝑑𝑙 𝑛, 𝑘, 𝑤
𝑗
4
𝐻0
1
𝑘 𝐱 𝑙 − 𝐱
𝐻 𝑚
1
is the mth order Hankel function of the first kind
𝑑𝑙 𝑘, 𝑤 are the loudspeaker signals to be derived
[1] Donley, J. & Ritz, C., “An efficient approach to dynamically weighted multizone wideband reproduction
of speech soundfields”, Proc. IEEE ChinaSIP 2015, pp. 60-64, 12-15 July 2015.
[2] W. Jin, W. B. Kleijn, and D. Virette, “Multizone soundfield reproduction using orthogonal basis
expansion,” Proc. IEEE ICASSP 2013, pp. 311–315
Solution is based on a weighted orthogonal basis expansion approach [1,2]

4. 4
http://bit.ly/WeightedMultizone
Weighting method controls leakage into
quiet zone at cost of quality in bright zone
• Multizone Occlusion
problem:
• Quiet zone in-line with
desired bright zone
• Difficult to control leakage
• Trade-off:
• Quality in Bright Zone vs
Quietness in Quiet Zone
Small weight
Large weight
Discrete:
Space 
Time 
Frequency 
(weighted actual
soundfield function)
How quiet does the quiet
zone need to be?

5. 5
• Only need to suppress leakage in the quiet zone down to
the threshold in quiet
• Possible only if the acoustic contrast between zones is large
enough
Case 1: The Hearing Threshold
Speech

6. 6
• Key idea: a masker in the quiet zone perceptually hides
surrounding frequency components leaked from the
bright zone
• Benefit: Less control via weighting needed – improve
bright zone quality
Case 2: Spreading functions
corresponding to local masking signal
2kHz Masker
Speech
• Max. SPL - small
weight, high bright zone
quality
• Min. SPL – large weight,
low bright zone quality
• Leaked SPL – masker
allowed to remain in
quiet zone

7. 7
Considering masking - reduces spatial error
in the bright zone and SPL in quiet zone
Benefit: Perceptually optimised trade-off between
quality and leakage
• Weights chosen by comparing reproduced speech with
spreading functions
(2)
reduction
Spatial error:
Speech
Spreading
function and
hearing
threshold
𝜖 𝑏(𝑛, 𝑘)

8. 8
Experimental evaluation to validate
proposed perceptual approach
Multizone Setup:
• Full circle of 65 loudspeakers
• Loudspeaker array diameter: 3m
• Zone diameters: 60cm
(enough space for a human head)
• Zone centres are 1.2m apart
• Reproduction capable of wideband
speech
• Direction of speech causes Multizone
Occlusion Problem (𝜃 ≈ 15°).
= Hearing threshold & Spreading
function (as used in audio coding
standards)

9. 9
• 10dB improvement in MSE
• Still high quality speech in the bright zone
Reduced bright zone error from
psychoacoustic masking
Mean Squared Error (MSE): MSE =
1
𝑀 𝑛=1
𝑀
𝑌𝑤(𝑛) − 𝑌(𝑛)
2
No masking
large weight
With masking
variable weight

10. 10
Reduced bright zone spatial error
from psychoacoustic masking
Magnitude difference (A, B):
Phase difference (C, D):
Maximum spatial error reduction:
28dB
Consequence of smaller weighting:
less loudspeaker power (max.
reduction = 65 %

11. 11
Conclusion: Exploiting perceptual
weighting within multizone soundfield
reproduction results in significant
advantages
• Improved error in bright zones with no perceptual cost in
adjacent zones
• MSE of speech: -69.8dB to -80.3dB (max)
• Spatial error: -7.4dB to -31.5dB (max)
• Reduced loudspeaker power (up to 65%)
• Improved reproduction when occlusion problem is present
Questions?