ITU Workshop on
Making Media Accessible to all: the Options and
the Economics
(Geneva, Switzerland, 24 – 25 October 2013)
Clean Audio
Harald Fuchs,
Fraunhofer IIS
harald.fuchs@iis.fraunhofer.de
Geneva, Switzerland, 24-25 October 2013
What is “Clean Audio”?
!
The term “Clean Audio” is defined in
the DVB specification for Audio and
Video coding as follows:
“Clean Audio refers to audio providing
improved intelligibility.
!   It is targeted for viewers with hearing
impairments,
!   but can as well serve as improvement
for listening in noisy environments like
airplanes.”
!
Geneva, Switzerland, 24-25 October 2013
2
Challenge: Finding the Right Mix
!
Audio mix with fixed balance
between dialogue and background is
always a compromise
Hearing impaired people require a
higher loudness of the dialogue
!   Non-native speakers need about 3dB
higher S/N
!   The listening environment has an
influence on the preferred setting of the
mix
!
Geneva, Switzerland, 24-25 October 2013
3
Options for Clean Audio
(1)
!   (2)
!   (3)
!   (4)
!
Transmit several different mixes
Transmit separate audio sources
Receiver-side Post-Processing
Object-based Dialogue
Enhancement
Geneva, Switzerland, 24-25 October 2013
4
(1) Transmit several different mixes
!
Pro
!
!
Backwards-compatible with existing
receivers
Cons
!
Only limited number of mixes possible
!
!
High additional data-rate
!
!
Number of parallel audio streams in
production workflow is one limiting factor
one complete audio stream per additional mix
No individual mix of speech/background
Geneva, Switzerland, 24-25 October 2013
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(2) Transmit separate audio sources
!
Pro
!
!
Individual mix of speech vs. background
Cons
Only backwards compatible if default
mix is sent in addition
!   high additional data-rate
!
!
!
-> 2 or 3 complete audio streams
Separate sources have to be available in
production workflow
Geneva, Switzerland, 24-25 October 2013
6
(3) Receiver-side Post-Processing
Processing to identify and enhance
speech parts of a mix audio signal
!   Pros
!
No additional data-rate
!   Requires no changes in production
!
!
Cons
Maximum enhancement is limited
!   Depends on signal characteristics
!   Depends on available CPU resources
!
Geneva, Switzerland, 24-25 October 2013
7
(4) Object-based Dialogue
Enhancement
!
Goal:
Enable similar flexibility as with
separate sources
!   Less bitrate overhead compared to
several mixes or separate sources
!
!
Solution:
Parametric, object-based side-info
!   Transmission of only one audio mix
!   Parameters sent with the mix, used in
receiver to change the balance of mix
!
Geneva, Switzerland, 24-25 October 2013
8
Signal Flow
Dialogue Enhancement
Geneva, Switzerland, 24-25 October 2013
9
Object-based Dialogue Enhancement
!
Pros
Flexibility: Individual mix of speech vs.
background is possible
!   Bitrate efficient: less overhead
compared to separate source delivery
!   Backward compatible: Default mix is
always present
!
!
Cons
!
Separate dialogue source in production
workflow, encoder update necessary
Geneva, Switzerland, 24-25 October 2013
10
Object-based Dialogue Enhancement
!
Technology
!
Based on MPEG Spatial Audio Object
Coding (SAOC) standard
!
!
Definition of Dialogue Enhancement Profile
(SAOC-DE) on-going
Standardization process on-going in
DVB
!
Add SAOC-DE as Advanced Clean Audio to
the DVB specification for audio and video
coding
Geneva, Switzerland, 24-25 October 2013
11
Listening Test
Geneva, Switzerland, 24-25 October 2013
12
Speech Intelligibility Listening Test
!
Test groups:
10 people with medium age related
hearing impairments
!   Group of 10 people with normal hearing
as reference group
!
!
German Sentence Test to measure
speech intelligibility
Sentences of five words with 10 options
for each word
!   Count correctly identified words
!
Geneva, Switzerland, 24-25 October 2013
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Speech Intelligibility Listening Test
!
Two different noise signals
!
Speech-shaped noise (SSN)
!
!
!
similar frequency characteristic as speech
Applause
Default mix of speech and noise
Set to a target level of 50% intelligibility
for the hearing-impaired group
!   In the test a slightly lower level was
achieved (46% and 34%)
!
Geneva, Switzerland, 24-25 October 2013
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Listening Test Results
!
Enhancement of 12 dB
!
!
intelligibility for both noise signals up to
80-90%
Similar to the intelligibility of normal hearing
listeners at the default mix
Normal-hearing listeners
SSN
Default mix
6 dB enhancement
12 dB enhancement
0%
20%
40%
60%
80%
100%
Speech Intelligibility / % correct
Geneva, Switzerland, 24-25 October 2013
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Listening Test Results (2)
!
Comparison of results for both noise
signals
!
!
Reference group: lower for Applause
Bigger difference for 6dB enhancement
between SSN and Applause compared to 12 dB
Normal-hearing listeners
Applause
Default mix
6 dB enhancement
12 dB enhancement
0%
20%
40%
60%
80%
100%
Speech Intelligibility / % correct
Geneva, Switzerland, 24-25 October 2013
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Conclusions
!
Personalization for improved intelligibility
!
!
Several options available for Clean Audio
!
!
with different advantages and disadvantages
New advanced Clean Audio solution
!
!
Enable the audience to change the balance of
dialogue vs. background
currently under standardization at DVB
Test Result: enhancement of 6 to 12 dB
!
useful range for adaptation to personal
preferences and listening environment
Geneva, Switzerland, 24-25 October 2013
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