development of a multipurpose audio transmission system on the internet
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Development of aMultipurpose Audio
Transmission Systemon the Internet
Takashi Kishida
Graduate School of Information Sciences,
Hiroshima City University, Japan
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Overview
Introduction Purpose
Audio communication scenes Implementation Evaluations
Conclusion
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Background
Spreading Broadband networks Real-time audio transmission ispopular
Various types of audiocommunications have beenattempted.
Distance lecture, Distancechorus etc.
We should consider requirements dependingon each scene.
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A problem in the Audio
Transmission Considerations in audio communication scenes
Robustness Reliability audio transmission An ability to recover packet losses on networks
Short delay End-to-end delays include processing delays of an
end node and transfer delays on a network
Trade-off between robustness and delays
Difficulty to realize both requirements at thesame time
Ex.) the case of about 150 ms
delays
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Purpose
Consideration on conditions ofrequirements for each audio
communication scenes
Development of a multipurpose
audio transmission system toadapt to various scenes
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Classification
LowHighVery HighSynchronization
Reliable
transmission
Smoothinteraction
Audiosynchronizati
onShort dela
Mainrequirement
HighMiddleLowRobustness
AnyLess than
400msITU-T G.114
Less than
100 ms
Allowable
delay
One to
many
Many to
many
Many to
many
Direction
Distance
lecture
Audioconference
Distancechorus
Scenes
Requirements
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Audio Communication Scenes
DistanceChorus
Distance Lecture
Audio conferenceConversation
100ms
400ms
End-to-end delay
Low High0ms
Robustness
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MRATMultipurpose RAT)
MRAT was developed onthe basis of RAT RAT(Robust Audio Tool) is
one of mbone tools. MRAT has three modes
to adapt to variousscenes
Chorus mode
shorter delays Conversation mode Broadcast mode
high
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Communication Scenes andmodes of MRAT
DistanceChorus
Distance Lecture
Audio conferenceConversation
100ms
400ms
End-to-end Delay
Low High0ms
Robustness
Original RAT
Shorter delays
High robustness
Chorusmode
Conversationmode
Broadcastmode
These twomodes areadded.
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Chorus mode
We tuned buffering parameters ofan audio device.
To realize delays less than about100ms
This mode is set up as to achieve shorterdelay
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Read length variation
This elapsed time related to delays.
The longer elapsed time is, the longer delays are.
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Evaluation of cushion
Cushion is close related to buffering time anddefined by elapsed time.
Cushion was decreased
to about 26 ms from 90ms by changingparameters.
MRAT realizes delays of70ms.(Cushion + An additional processing delay =
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We use Reed-Solomon block codeReed-Solomon block code has advantagein burst errors
Broadcast mode
To achieve robustness
Advantage in a real-time application
FEC Forward Error
Correctionsenderreceiver
generating redundant packet each somepacketsrecovery from redundant packets in thecase of packet losses
Broadcast mode is set up as to achieve robustness.
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State of Implementation
All modes are completed Almost all audio codec are
implemented in Broadcast mode
Confirmation of implementation
SoundBlaster Live! ValueSoundcard
Vine Linux 2.1,Vine Linux2.1.5,VineLinux2.5
OS
Pentium 1.0GHz Pentium300MHzCPU
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Evaluations of MRAT
Measurement of delays on eachmode
FEC Performance measurement ofBroadcast mode Practical experiments
Distance Chorus using Chorus mode Distance seminar using Broadcast
mode
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Experimental environment ondelays
Ethernet100Mbps
Host A Host B
Transmit
Recording PC
Record Record
Metronom
e
CPU Pentium
600MHz
CPU Pentium
1GHz
We measured thedifference of delaysbetween (a) and (b).
(a) Sound ofmetronome
(b) Soundvia Host B
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FEC Performance measurement ofBroadcast mode
Ethernet100Mbps
Lossgenerator
Host A Host BCPU Pentium 600MHz
OS Vine Linux2.5
CPU Pentium 1GHz
OS Vine Linux2.1
CPU Pentium 300MHz
OS Vine Linux2.1
Packet lossgenerated
1,2,4,6,8,10%
Measure after
decoding RScodes
We compared the experimental values and
the theoretical values
Experimentalvalues
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Result
0
1
2
3
4
5
0 2 4 6 8 10 12
Packet loss rate before applying FEC (%)
Packetlossrateafterap
plyingFE
(15,13)Experimental value
(15,13)Theoretical value
(15,12)Experimental value
(15,12)Theoretical value
(15,11)Experimental value
(15,11)Theoretical value
(1513)
(15
12)
(1511)
The theoretical values and the experimental valuesare almost the same.Packet loss rate can be decreased from 11% to less than 1% by using FEC.
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Di t S i i
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Hiroshima City Univ.
Hiroshima Univ.
SagaUniv.
Experimen
tal IPNetwork(ATM
45Mbps)
Jitter 4ms
Avg. packet loss
0.000058 %
RTT 14.8ms
Hiroshima City Univ. SagaUniv.
Jitter 6ms
Avg. packet loss0.120%
RTT 8.5ms
Hiroshima-city Univ.
-- Hiroshima Univ.Audio MRAT(160Kbps)
Movie Mpeg2ts(5Mbps)
Requirementbandwidth
Distance Seminar usingBroadcast mode
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The results of error recovery for only 100 seconds
as a typical part during the seminar
Error recovery of packetlosses using Broadcast mode
0.0%
1.0%
2.0%
3.0%4.0%
5.0%
6.0%
7.0%
0 20 40 60 80 100Time (sec)
Packetloss
rate(%)
Before applying FEC
After applying FEC
Packet losses are almost recovered by usingbroadcast mode
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Hiroshima City Uni
akushima Elementary School(Main melody)
inami-Kanon Elementary(Sub melody)
Experimental IPnetwork
10Mbps, widearea Ethernet
7075ms
DistanceChorus
Accompaniment
Accompaniment
Accompaniment
Submelod
y
Main+Sub
melody
Accompaniment
+Sub melody
Accompaniment
+Main melody
Mainmelody
7 msJitter
2.1 msTransfer delay
512 kbpsRequirementbandwidth
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Conclusion Classification of audio communication
scenes Development of a multipurpose audio
transmission system, MRAT, and itsevaluation Some practical experiments such as a
distance chorus at multi-points and
distance seminars
Our system can be used in multipleaudio communication scenes.
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Future Problems New applications using each mode Dynamic and adaptive changing of
three modes depending on therequirements
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Scalability of Distance Chorus
How wide area torealize distancechorus?
Light propagation:21000km in 70ms
We think practicalchorus is inMetropolitan networkwithin an area of afew hundreds
kilometers.
Considering this restriction, distance chorusis not realized in the worldwide on theInternet
The mostideal
situation
Its realizable as a regionalnetwork
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Bandwidth of MRAT
6652.8GSM
160128VDVI
160128DVI
8064G726-40
12096G726-40
160128G726-40
200160G726-40320256A-law
320256-law
640512Linear-16
Bandwidth ofAfter RS encode[kbps]
RS encodeBandwidth[kpbs]
Encoding
h li f d
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The quality of soundcomparison of MRAT and RAT
36.4RAT
3.4MRAT(Broadcast mode)
The detected number of
noise
This is the result that the noise of MRAT and RAT
was measured.FFT was used for the measurement.
li h i
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To realize the DistanceChorus
70ms
accompaniment
Mainmelody
Submelody
Ideal tolerant delay
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End-to-end delay bounds
150ms
Delay not Perceived
In most cases
400ms
Natural
Interaction
ITU-T G.114 ITU-T G.114
150m
s
400m
s
Best medium
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