An audio quality evaluation of digital radio system
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AN AUDIO QUALITY EVALUATION OF DIGITAL RADIO SYSTEMS
GUIDED BY; PRESENTED BY;MR. ANOOP CHANDRAN P ROJITH THOMAS
ASST. PROFESSOR MTECH-ECE
CAARMEL ENGG. COLLEGE CAARMEL ENGG. COLLEGE
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SCOPE
• It is to provide a Broadcasting Standard for the DigitalAudio Systems designed for delivery of high qualitydigital audio programme and data services formobile,portable and fixed reception from terrestrial orsatellite transmitters in the VHF/UHF as well as fortransmission through cable networks
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INTRODUCTION
• Radio has changed the world of communicationduring the last decade and even now remainsrelevant in modern society.
• Nikola Tesla was the first to talk about utilizing these signals for the use of communication.Macroni is the first who introduced the radio system.
• Radio is the medium for communication. It transmitsmessage via Radio waves.And It is a communicationsystem based on broadcasting electromagnetic waves
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• Mainly there are two types of radio systems;
a)Analog Radio System
b)Digital Radio System
• Major criteria for designing radio system is;
1)Audio Quality
2)Channel Capacity
• Radio is a democratic medium. So it has wide applications in the field of Education,Entertainment,Medical,News and even for Businesses also.
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EXISTING SYSTEM
• The Existing System is Analog radio Systems
• They are divided into two;
>AM Radio Broadcasting Systems.
>FM Radio Broadcasting Systems.
• AM Broadcasting System is mainly divided into;
>Mid frequency:530 to 1600 KHz
>Short Wave 1 &2
SW1:2.3 to 7.0 MHz
SW2:7.0 to 22 MHz
• FM Radio Ranges from 88 to 106 MHz
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EVALUATION OF EXISTING
SYSTEM
• Evaluation of analog radio system is mainly done for FMsystem using MUSHRA Method.
• The Audio Quality for Analog Broadcasting systems are;
>FM :72% -Good
>SW2 :63% -Fair
>SW1 :60% -Fair
>MF :40% -Fair
• From this we can conclude that the audio quality ofanalog system is not suitable for providing betterservice.
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DISADVANTAGES
• It has Transmission and Reception limitations.
• Due to increase in the usage of number of bands, thecongestion is occurs and it lead to the decline inreception quality.
• It suffers to provide uniform reception qualitythroughput.
• Insufficient use of spectrum; Spectrum Efficiency is low.
• It offers poor audio quality due to less Noise immunity.
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PROPOSED SYSTEM
• In order to provide better quality of service, the digitalradio system is introduced.
• The digital radio transmitter compresses the audiosignals using an AUDIO CODEC and it transmits as bitstreams to the terminals
• And at receiver; the reconstruction of signal is occurfrom bit streams.
• Digital system has capability to transfer throughterrestrial, satellite and even through cables.
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ADVANTAGES
• More robust than analog and it can be transmittedsuccessfully at lower transmitter power.
• It uses Coded Multi carrier Modulation(PCM) in orderto provide improved reception quality.
• Provides wide coverage area with less implementingcost.
• Spectrum efficiency is improved and also provide highchannel capacity.
• Introduction of data compression techniques help toimprove sound quality at low bit rates.
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EVALUATION OF AUDIO QUALITY
• The evaluation is mainly for finding the mean audioquality of all systems.
• In order for that; four terrestrial digital domestic radiosystems are considered. They are;
>DAB
>DAB+
>HD Radio
>T-DMB
• Each system has its own audio codecs.So,the audioquality depends not only on the Bit Rate but also uponthe System type.
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• Evaluation is at different bit rates in order to provide areference to determine Optimal Bit Rate for giventarget audio quality.
• The Audio Quality adopted for each system are;
>DAB :MPEG-1 LAYER II(.mp2)
>DAB+ :HE-AAC v2(.aac)
>HD RADIO :HDC(.hd)
>T-DMB :MPEG-4 ER-BSAC(.mp4)
• In order to get accurate results, the evaluations hassetup in the same environment for all systems.
• The evaluation process is conducted in two phasesnamed as;
>PHASE-I >PHASE-II
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EVALUATION SETUP
• Evaluation setup mainly consist of;
>Audio Samples
>Digital Radio Equipment
• The evaluation process are;
>Test Signal Acquisition.
>Subjective Evaluation Method(MUSHRA).
>Pre Screening And Post Screening.
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AUDIO SAMPLES
• The audio samples used for test should be able torecognize the performance difference between thecodecs and contain the realistic contents for thedigital radio services.
• Nine audio samples are used for evaluation and aresubdivided into different categories.
• The sample length for each sample is 10-15 secondsand in stereo format with sampling frequency of 48KHz.
• In HD Radio, it supports only the sampling rate of44.1KHz.So audio samples with sampling rate of44.1KHz were prepared from 48KHZ.
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AUDIO SAMPLES USED IN EVALUATIONNAME TYPE CHARACTERISTICS
SPEECHFEMALE,ENGLISH
MALE,KOREAN
FEMALE ,ENGLISH
SINGING
COLLOQUIAL STYLE
LITERARY STYLE
MUSIC
POP MUSIC
JAZZ
CLASSICAL
VOCAL,GUITAR,DRUM,KEYBOARD
WIND,BRASS,DRUM
STRINGS,PERCUSSION,WIND
MIXED
SPEECH+MUSIC
SPORTS BROADCASTING
SONGS+BACKGROUND
MALE SPEECH,STRINGS,WIND.PERCUSSIONS
FEMALE SPEECH,AUDIENCE SHOUTING
CHILDREN’S SONG,PERCUSSION,SOUND EFFECT
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DIGITAL RADIO EQUIPMENT
SYSTEM MANUFACTURE AND ENCODER MODEL
MANUFACTURER AND DECODER MODEL
DAB Factum ElectronicsMAP250E
PNP Network Technologies
PN3021P
DAB+ Factum ElectronicsMAP250E
PNP Network Technologies
PN3021P
HD Radio Broadcast ElectronicsXpi 10
Day SequerraM4.0X
T-DMB PixtreePix VR-E11011
PNP Network Technologies
PN3021P
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TEST SIGNAL ACQUISITION
• The test signal for evaluation are acquired directlyfrom digital radio equipment.
• Audio signal is played from computer and transmittedto audio encoder in the form of PCM through audiointerface equipment.
• The sampling rate is selected according to digital radiosystem.
• Audio encoder compress audio signal to bit streamand transmitted through wireless channel usingOFDM.
• In reciever,decoder converts bit streams to audiosignals and saved in computer as PCM format.
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BLOCK DIAGRAM
COMPUTER1
DIGITAL
AUDIO
INTERFACE
AUDIO
ENCODER
RF
TRANSMITTER
AUDIO
DECODER
RF
RECEIVERCOMPUTER 2
OF
DM
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• In evaluation, the bits rate of encoder is set fordifferent values.
• Therefore,
4 bit rates X 4 Systems X 9 Samples=144 test signals
is used for evaluation.
• Test Bit Rates used for evaluation is ;
SYSTEMS DAB DAB+ HD RADIO T-DMB
BIT RATE
(Kbps)
64
96
128
192
24
48
64
96
24
28
64
96
48
64
96
128
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SUBJECTIVE EVALUATION METHOD
• Subjective Evaluation is done by using MUSHRAMethod(Multiple Stimuli With Hidden Reference AndAnchor).
• It uses STEP ver.0.10 Program and which is provided byAudio Research Lab(ARL).
• In this method, the grading system is provided witheach audio samples.
• In this method contains;
>REFERENCE AND HIDDEN REFERENCE SIGNAL.
>ANCHORS.
>TEST SIGNALS.
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TESTING ENVIRONMENT
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• In phase 1 test, evaluates the audio quality for eachsystem(evaluation of four bit rates of each system).
• On every trials each subjects(listeners) randomlylistens;
1 REF+1 HR+2 ANC+4 SIG(diff. bit rate)=8 SIGNALS
• So it conducts 4 system X 9 audio samples=36 trials.
• In Phase 2 test, evaluates the audio quality as afunction of four systems.
• On every trials each subjects(listeners) randomlylistens;
1 REF+1 HR+2 ANC+4 SIG(diff. system)=8 SIGNALS
• So it conducts 2 groupsX9 audio samples=18 trials.
• After each trial, the listener marks the grade.
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PRE SCREENING AND POST SCREENING
• In order to provide a guaranteed audio qualityassessment, each listener must have a normal hearingability. So before main evaluation Pre-screening isconducted.
• Nine different audio samples are impaired(processed)using 3.5 and 7KHz LPF or an HE AAC v2 at 32kbps oran HE-AAC V2 at 28 Kbps.
• Then participants first listen to the original sample andafter a short break again original and impaired signals.Then they ask which is the original.
• This process continues for nine audio samples and passthe test only when they give correct answer for 8 of 9.
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• 22 listeners applied for evaluation test and one failedthe pre screening. So the remaining 21 listeners wereselected for final participation.
• After PHASE 1 test, a Post Screening test wasconducted in order to ensure a fair assessment ofquality.
• By analyzing of evaluation result of each listener, thelisteners who are believed to make consistent gradingand appropriate quality discrimination are selected.
• Six listeners failed in post screening, thereforeevaluation results of 15 were collected and statisticalanalysis is performed for each subject data.
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EVALUATION RESULTS
A.PHASE 1 TEST
• This figure shows the mean audio quality of each system as a function of bit rates.
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• It helps us to determine necessary bit rate for a giventarget audio quality for each sub system.
• The quality of DAB at 64 and DAB+ at 24 kbps arelow. The reason is for this is encoders used areoptimized for higher bit rates.
• And also HD Radio at 96 kbps does not showexpected quality; the reason might be the nonoptimized encoder.
B.PHASE 2 TEST
• It is to confirm evaluation consistency of PHASE 1.
• Two groups of similar audio quality were determinedfrom all of the members in each system.
> MID QUALITY >HIGH QUALITY
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TEST SIGNAL SET IN A SINGLE TRIAL OF PHASE 1 AND 2
- Test Signal for Phase 1 test.
- Test Signal for Phase 2 test.
GROUP OF TEST CASES USED IN PHASE 2 TEST
SYSTEM DAB DAB+ HD Radio T-DMB
BIT RATE
(Kbps)
64 24 24 48
96 48 48 64
128 64 64 96
192 96 96 128
GROUP DAB DAB+ HD Radio T-DMB
MID QUALITYHIGH QUALITY
128Kbps192Kbps
48Kbps96Kbps
48Kbps96Kbps
64Kbps128Kbps
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• The mean audio quality of each groups;
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C.ANALYSIS
• Comparing audio quality of the systems that was intwo phases.
• If the two grades of a system are in the range ofequality, then evaluation consistency between twophases are guaranteed.
• The results of comparison is as;
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• This unsatisfactory condition are occur due to;
>MUSHRA method measures the relative qualityamong the test signals in each trial.
• In First Case: HD radio(High Quality Group)
>Each signals in the phase 2 test are higher valuesignals in the PHASE 1.
>It can be explained as;
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• In Second Case: T-DMB(Mid Quality Group)
>Each signals in the phase 2 test are higher valuesignals in the PHASE 1.
>It can be explained as;
• This difference is occur due to relatively largedifference in their evaluation setup.
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• From this; the mean audio quality of system is givenas;
• DAB 128,HD RADIO 48,DAB+ 48,HD RADIO 64 provide better audio quality than FM.
• DAB 64,T-DMB 96,DAB+ 96,T-DMB 128,DAB 192 can provide better audio quality like CD.
FM
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CONCLUSION
• Subjective audio quality of 4 digital systems areevaluated using MUSHRA METHOD using nine audiosamples.
• Evaluation process consist of two phases. Phase 1 isfor evaluating quality on the basis of function of bitrates. Phase 2 is for evaluating on the basis offunctions of system.
• The results are compared and finally mean audioquality is calculated.
• This results can be used as a reference to determinethe optimal channel capacity for a given target audioquality.
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REFERENCE
• F.HOFMANN,C.HANSEN AND W.SCHAFER,”DIGITAL RADIOMONDIALE (DRM) DIGITAL SOUND BROADCASTING IN THE AMBANDS , ”IEEEE TRANS. BROADCAST.,VOL.49,NO.,PP.319-328,SEP . 2003.
• RADIO BROADCASTING SYSTEMS: DIGITAL AUDIOBROADCASTING TO MOBILE , PORTABLE AND FIXED RECEIVERS ,ETSI EN 300 401 VER 1.4.1.JAN 2006.
• “METHOD OF SUBJECTIVE ASSESSMENT OF INTERMIDATEQUALITY LEVEL OF CODING SYSTEMS”,ITU-R BS.1534,2003.
• “SUBJECTIVE TRAINING EVALUATION PROGRAM”,ARL 2004.
• “EBU EVALUATION OF MULTICHANNEL AUDIO CODECS”,EBU2007.
• “EBU LISTENING TEST ON INTERNET CODECS”,EBU TECHNICALREVIEW 2000.
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