Comparison of microphone distances for real-time reverberation enhancement system using optimal source distribution technique

Comparison of microphone distances
for real-time reverberation enhancement system
using optimal source distribution technique
Atsushi Marui (Tokyo University of the Arts)
Motoki Yairi (Kajima Technical Research Institute)
Toru Kamekawa (Tokyo University of the Arts)

Background
• Musicians preparing for a live performance want to experience the spatial
impression of the concert hall
• Difficult to try the actual concert hall before the performance
(geographically, financially, …)
• Reverberation enhancement systems
• Reverberation enhancement by adding artificial reverberation to
microphone captured instrument sounds
August 9th, 2018 Marui, Yairi, Kamekawa 1

Background
• Supplying reverberation in a smaller
rehearsal hall to recreate a large hall
• E.g., Lokki et al. (2009)

Background
• Supplying reverberation in near
anechoic room
• E.g., Ueno et al. (1996, 2003),
Tsuchikura et al. (2012)
several subjects, who performed the instruments,
strings, brass or woodwinds.
3.1.1. System
Figure 4: Brock diagram of Experimental system
t
p
3
T
m
p
g
A
t
3
I
v
l
F
s
p

Background
anechoic room
• E.g., Ueno et al. (1996, 2003),
• Controlling reverberation for
musically adequate amount
• E.g., Ko and Woszczyk (2015)
between the objective parameters and musicians’
evaluations. The study also revealed two primary
perceptual dimensions from the musicians’ subjective
judgments on different acoustic aspects: ‘Overall
quality’ and ‘Timbre.’ ‘Overall quality’ judgment was
varied by the fact whether the musicians were familiar
with the halls, however, ‘Timbre’ was an independent
quality that was correlated with the frequency variation
of Early Decay Time (EDT).
The authors reported preliminary subjective evaluation
results in 2012 from an investigation of five string
quartets [11]. The study showed musicians’ significant
preference for augmented acoustics produced by a new
active acoustics system and discovered several
contributing perceptual attributes to their preference.
In this paper, the previous results are combined with a
new set of result from the experiments with six more
string quartets, a total of 44 musicians.
1 BACKGROUND
McGill University’s Virtual Acoustics Technology
(VAT) system utilizes high-resolution impulse
responses of various unique acoustic spaces, measured
since 2005 by the VAT Lab Research Group [12]. The
acoustic responses were measured using a custom sound
source system consisting of 2 subwoofers, 2 super-
tweeters and 8-14 accompanying loudspeakers
space immersing the musicians in a desired acoustic
response. In total, 16 custom dodecahedron
loudspeakers along with 4 sub-woofers are used. Each
dodecahedron unit encloses 12 full range drivers, which
means that 192 speaker drivers are projecting acoustic
responses into the hall. The speakers are carefully
positioned to cover the entire floor area as well as the
vertical space of the room. They have been calibrated
with measurement tools and the ears of expert sound
engineers.
Figure 1: VAT system in MMR at McGill University.
Eight microphones cover the floor area above musicians
and the signals are amplified and converted to the
digital domain at 24bit / 96kHz resolution. Preamplifiers

Background
anechoic room
• E.g., Ueno et al. (1996, 2003),
Our Goal
• Realistic reverberation support
in smaller setup
• In an ordinary practice room

Background
anechoic room
• E.g., Ueno et al. (1996, 2003),
Our Goal
in smaller setup
Binaural Reproduction
• A small-scale speaker array
implementing crosstalk
cancellation using Optimal
Source Distribution method

Background
anechoic room
• E.g., Ueno et al. (1996, 2003),
Our Goal
in smaller setup
Binaural Reproduction
• A small-scale speaker array
implementing crosstalk
cancellation using Optimal
Source Distribution method
Microphone Setting?
• Close mic
• sounds not good
• Far mic
• room reverb makes feedback

Playing an instrument in a room
ADCDAC
1.5 m
0.75 m
Mic 4
Mic 3
Mic 2
Mic 1
pow.amp.convolvermic.amp.
ß
ßß
ß

The system used for the experiment
ADCDAC
1.5 m
0.75 m
Mic 4
Mic 3
Mic 2
Mic 1
ß
ßß
ß

Questions addressed in this study
• How is the quality of binaural reproduction of room reverberation
• Usable in practice situations?
• Comparable with the actual room?
• How close or far should the microphone be?

ADCDAC
1.5 m
0.75 m
Mic 4
Mic 3
Mic 2
Mic 1
ß
ßß
ß
Which room?

Studio A, Senju Campus, Tokyo University of the Arts

Binaural impulse response measurement

ADCDAC
1.5 m
0.75 m
Mic 4
Mic 3
Mic 2
Mic 1
ß
ßß
ß
Which room?

Control Room for Studio A, Senju Campus, Tokyo University of the Arts

Experimental setup

Microphone setup
DPA 4099
Schoeps CMC641
Schoeps CMC64
Mic 4
Mic 3
Mic 2
Mic 1

ADCDAC
1.5 m
0.75 m
Mic 4
Mic 3
Mic 2
Mic 1
ß

Experimental Variables
Independent Variable
• 4 mic placements + 1 actual room
• Mic on the instrument,
15cm, 30cm, 75cm above
• Studio A
Dependent Variables
• timbre（音色）
• spatial impression（空間印象）
• reverberation（残響感）
• ease of playing（演奏のしやすさ）
• overall quality（総合的な良さ）
• preference（個人的な好み）
Method
• Scheffé’s Pairwise Comparison
• Take 2 stimuli from 5 stimuli
and rate by how much one is higher in a given attribute (in 11-pts)
• For all possible pairs: 5 x (5–4) = 20 pairs
• All pairs were given in an random order in single blinded manner (except for
the actual room where participant had to walk in and out)

Reducing Number of Stimuli Presentations
1
2
3
4
5
6
7
8
9
10
C
A
E
D
B

Participants
• 3 professional violinists
• More than 25 years of violin experiences
• Members of Tokyo University of the Arts Philharmonia Symphony
Orchestra
• Native Japanese language users
• Have prior experiences in taking subjective experiments

Sample Reponses
timbre
spatial
reverb
ease
quality
pref
timbre
spatial
reverb
ease
quality
pref
The current setting (A) can be rated as… compared to the previous setting (M)
previous better current better

Results
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
Timbre
Spatial Impression
Preference
Ease of Playing
Overall Quality
Reverberation
A1 2 3 4
A12 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
• 1–4 are mic placement
• 1 is the closest
(violin mounted)
• 4 is the furthest
• A is the room
• Bars connecting stimuli show
statistically significant
differences in α=.05 level

Results
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
Timbre
Spatial Impression
Preference
Ease of Playing
Overall Quality
Reverberation
A1 2 3 4
A12 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
• Studio A (actual room) is
rated the highest

Results
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
Timbre
Spatial Impression
Preference
Ease of Playing
Overall Quality
Reverberation
A1 2 3 4
A12 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
rated the highest
• Further microphones are
rated higher in most cases

Results
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
-2 -1 0 +1 +2
Timbre
Spatial Impression
Preference
Ease of Playing
Overall Quality
Reverberation
A1 2 3 4
A12 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
A1 2 3 4
rated the highest
• No significant differences
between furthest microphone
and actual room on:
• Reverberation
• Ease of Playing
• Overall Quality
• Preference

Summary
• Goal: to provide a realistic reverberation to instruments players
• Method:
• provide real-time binaural convolution reverb
• loudspeaker array using crosstalk cancellation
• Experiment: 5 stimuli were rated on 6 attributes in pairwise comparison
• Stimuli: 4 microphone distances and 1 actual live room
• Attributes: timbre, spatial impression, reverberation, ease of playing,
overall quality, preference
• Results:
• Actual live room was rated highest for all attributes
• Further located microphones are rated higher in most cases
• No significant differences between furthest microphone and actual
room on: Reverberation, Ease of Playing, Overall Quality, Preference

Comparison of microphone distances for real-time reverberation enhancement system using optimal source distribution technique

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Comparison of microphone distances for real-time reverberation enhancement system using optimal source distribution technique

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