An audio quality evaluation of digital radio system
AN AUDIO QUALITY EVALUATION OF DIGITAL RADIO SYSTEMSGUIDED BY; PRESENTED BY; MR. ANOOP CHANDRAN P ROJITH THOMAS ASST. PROFESSOR MTECH-ECE CAARMEL ENGG. COLLEGE CAARMEL ENGG. COLLEGE
SCOPE• It is to provide a Broadcasting Standard for the Digital Audio Systems designed for delivery of high quality digital audio programme and data services for mobile,portable and fixed reception from terrestrial or satellite transmitters in the VHF/UHF as well as for transmission through cable networks
INTRODUCTION• Radio has changed the world of communication during the last decade and even now remains relevant 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 transmits message via Radio waves.And It is a communication system based on broadcasting electromagnetic waves
• 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.
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
EVALUATION OF EXISTING SYSTEM• Evaluation of analog radio system is mainly done for FM system 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 of analog system is not suitable for providing better service.
DISADVANTAGES• It has Transmission and Reception limitations.• Due to increase in the usage of number of bands, the congestion is occurs and it lead to the decline in reception quality.• It suffers to provide uniform reception quality throughput.• Insufficient use of spectrum; Spectrum Efficiency is low.• It offers poor audio quality due to less Noise immunity.
PROPOSED SYSTEM• In order to provide better quality of service, the digital radio system is introduced.• The digital radio transmitter compresses the audio signals using an AUDIO CODEC and it transmits as bit streams to the terminals• And at receiver; the reconstruction of signal is occur from bit streams.• Digital system has capability to transfer through terrestrial, satellite and even through cables.
ADVANTAGES• More robust than analog and it can be transmitted successfully at lower transmitter power.• It uses Coded Multi carrier Modulation(PCM) in order to provide improved reception quality.• Provides wide coverage area with less implementing cost.• Spectrum efficiency is improved and also provide high channel capacity.• Introduction of data compression techniques help to improve sound quality at low bit rates.
EVALUATION OF AUDIO QUALITY• The evaluation is mainly for finding the mean audio quality of all systems.• In order for that; four terrestrial digital domestic radio systems are considered. They are; >DAB >DAB+ >HD Radio >T-DMB• Each system has its own audio codecs.So,the audio quality depends not only on the Bit Rate but also upon the System type.
• Evaluation is at different bit rates in order to provide a reference to determine Optimal Bit Rate for given target 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 has setup in the same environment for all systems.• The evaluation process is conducted in two phases named as; >PHASE-I >PHASE-II
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.
AUDIO SAMPLES• The audio samples used for test should be able to recognize the performance difference between the codecs and contain the realistic contents for the digital radio services.• Nine audio samples are used for evaluation and are subdivided into different categories.• The sample length for each sample is 10-15 seconds and in stereo format with sampling frequency of 48 KHz.• In HD Radio, it supports only the sampling rate of 44.1KHz.So audio samples with sampling rate of 44.1KHz were prepared from 48KHZ.
AUDIO SAMPLES USED IN EVALUATIONNAME TYPE CHARACTERISTICS FEMALE,ENGLISH SINGINGSPEECH MALE,KOREAN COLLOQUIAL STYLE FEMALE ,ENGLISH LITERARY STYLE POP MUSIC VOCAL,GUITAR,DRUM,KEYBOARDMUSIC JAZZ WIND,BRASS,DRUM CLASSICAL STRINGS,PERCUSSION,WIND SPEECH+MUSIC MALE SPEECH,STRINGS,WIND. PERCUSSIONSMIXED SPORTS BROADCASTING FEMALE SPEECH,AUDIENCE SHOUTING CHILDREN’S SONG,PERCUSSION, SONGS+BACKGROUND SOUND EFFECT
DIGITAL RADIO EQUIPMENT SYSTEM MANUFACTURE AND MANUFACTURER AND ENCODER MODEL DECODER MODEL DAB Factum Electronics PNP Network MAP250E Technologies PN3021P DAB+ Factum Electronics PNP Network MAP250E Technologies PN3021P HD Radio Broadcast Electronics Day Sequerra Xpi 10 M4.0X T-DMB Pixtree PNP Network Pix VR-E11011 Technologies PN3021P
TEST SIGNAL ACQUISITION• The test signal for evaluation are acquired directly from digital radio equipment.• Audio signal is played from computer and transmitted to audio encoder in the form of PCM through audio interface equipment.• The sampling rate is selected according to digital radio system.• Audio encoder compress audio signal to bit stream and transmitted through wireless channel using OFDM.• In reciever,decoder converts bit streams to audio signals and saved in computer as PCM format.
• In evaluation, the bits rate of encoder is set for different 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 64 24 24 48 BIT RATE 96 48 28 64 (Kbps) 128 64 64 96 192 96 96 128
SUBJECTIVE EVALUATION METHOD• Subjective Evaluation is done by using MUSHRA Method(Multiple Stimuli With Hidden Reference And Anchor).• It uses STEP ver.0.10 Program and which is provided by Audio Research Lab(ARL).• In this method, the grading system is provided with each audio samples.• In this method contains; >REFERENCE AND HIDDEN REFERENCE SIGNAL. >ANCHORS. >TEST SIGNALS.
• In phase 1 test, evaluates the audio quality for each system(evaluation of four bit rates of each system).• On every trials each subjects(listeners) randomly listens; 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 a function of four systems.• On every trials each subjects(listeners) randomly listens; 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.
PRE SCREENING AND POST SCREENING• In order to provide a guaranteed audio quality assessment, each listener must have a normal hearing ability. So before main evaluation Pre-screening is conducted.• Nine different audio samples are impaired(processed) using 3.5 and 7KHz LPF or an HE AAC v2 at 32kbps or an HE-AAC V2 at 28 Kbps.• Then participants first listen to the original sample and after a short break again original and impaired signals. Then they ask which is the original.• This process continues for nine audio samples and pass the test only when they give correct answer for 8 of 9.
• 22 listeners applied for evaluation test and one failed the pre screening. So the remaining 21 listeners were selected for final participation.• After PHASE 1 test, a Post Screening test was conducted in order to ensure a fair assessment of quality.• By analyzing of evaluation result of each listener, the listeners who are believed to make consistent grading and appropriate quality discrimination are selected.• Six listeners failed in post screening, therefore evaluation results of 15 were collected and statistical analysis is performed for each subject data.
EVALUATION RESULTSA.PHASE 1 TEST• This figure shows the mean audio quality of each system as a function of bit rates.
• It helps us to determine necessary bit rate for a given target audio quality for each sub system.• The quality of DAB at 64 and DAB+ at 24 kbps are low. The reason is for this is encoders used are optimized for higher bit rates.• And also HD Radio at 96 kbps does not show expected quality; the reason might be the non optimized encoder.B.PHASE 2 TEST• It is to confirm evaluation consistency of PHASE 1.• Two groups of similar audio quality were determined from all of the members in each system. > MID QUALITY >HIGH QUALITY
TEST SIGNAL SET IN A SINGLE TRIAL OF PHASE 1 AND 2SYSTEM DAB DAB+ HD Radio T-DMB 64 24 24 48 96 48 48 64BIT RATE(Kbps) 128 64 64 96 192 96 96 128 - Test Signal for Phase 1 test. - Test Signal for Phase 2 test. GROUP OF TEST CASES USED IN PHASE 2 TEST GROUP DAB DAB+ HD Radio T-DMB MID QUALITY 128Kbps 48Kbps 48Kbps 64Kbps HIGH QUALITY 192Kbps 96Kbps 96Kbps 128Kbps
C.ANALYSIS• Comparing audio quality of the systems that was in two phases.• If the two grades of a system are in the range of equality, then evaluation consistency between two phases are guaranteed.• The results of comparison is as;
• This unsatisfactory condition are occur due to; >MUSHRA method measures the relative quality among the test signals in each trial.• In First Case: HD radio(High Quality Group) >Each signals in the phase 2 test are higher value signals in the PHASE 1. >It can be explained as;
• In Second Case: T-DMB(Mid Quality Group) >Each signals in the phase 2 test are higher value signals in the PHASE 1. >It can be explained as;• This difference is occur due to relatively large difference in their evaluation setup.
• From this; the mean audio quality of system is given as; FM• 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.
CONCLUSION• Subjective audio quality of 4 digital systems are evaluated using MUSHRA METHOD using nine audio samples.• Evaluation process consist of two phases. Phase 1 is for evaluating quality on the basis of function of bit rates. Phase 2 is for evaluating on the basis of functions of system.• The results are compared and finally mean audio quality is calculated.• This results can be used as a reference to determine the optimal channel capacity for a given target audio quality.
REFERENCE• F.HOFMANN,C.HANSEN AND W.SCHAFER,”DIGITAL RADIO MONDIALE (DRM) DIGITAL SOUND BROADCASTING IN THE AM BANDS , ”IEEEE TRANS. BROADCAST.,VOL.49,NO.,PP.319-328, SEP . 2003.• RADIO BROADCASTING SYSTEMS: DIGITAL AUDIO BROADCASTING TO MOBILE , PORTABLE AND FIXED RECEIVERS , ETSI EN 300 401 VER 1.4.1.JAN 2006.• “METHOD OF SUBJECTIVE ASSESSMENT OF INTERMIDATE QUALITY LEVEL OF CODING SYSTEMS”,ITU-R BS.1534,2003.• “SUBJECTIVE TRAINING EVALUATION PROGRAM”,ARL 2004.• “EBU EVALUATION OF MULTICHANNEL AUDIO CODECS”,EBU 2007.• “EBU LISTENING TEST ON INTERNET CODECS”,EBU TECHNICAL REVIEW 2000.