Audio CodingAudio Coding

MPEG1 Layers I, II, IIIMPEG1 Layers I, II, III

MPEG2MPEG2

MPEG4MPEG4

Sherida SubratiAnthony Caliendo

OverviewOverview

• Explanation of CodecsExplanation of CodecsMPEG1 – Layer I, II, III (Differences)MPEG1 – Layer I, II, III (Differences)MPEG2 – Basic OverviewMPEG2 – Basic OverviewMPEG4 – Possible ApplicationsMPEG4 – Possible Applications

• Applications & Sound Samples UsedApplications & Sound Samples Used• Results & ExplanationResults & Explanation

File Size, Bitrate, & QualityFile Size, Bitrate, & QualityWaveform ComparisonWaveform Comparison

• Summary & QuestionsSummary & Questions

Sub-Band Coding OverviewSub-Band Coding Overview

• Size of sub-Size of sub-bands variesbands varies

• Varying Varying application of application of psychoacoustpsychoacoustic modelic model

MPEG1 – Layer I & IIMPEG1 – Layer I & II

• Time Frequency MappingTime Frequency Mapping Polyphase Filter BankPolyphase Filter Bank 32 Equal Bands32 Equal Bands

• Psychoacoustic ModelPsychoacoustic Model 512-point FFT & 1024-point FFT respectively512-point FFT & 1024-point FFT respectively Tonal & Noise MaskingTonal & Noise Masking

• QuantizerQuantizer Scale Factor: 6 bitsScale Factor: 6 bits Layer II – Allows 3 successive scale factors & Layer II – Allows 3 successive scale factors &

uses 1-3 depending on how much they differuses 1-3 depending on how much they differ

MPEG1 – Layer I & II MPEG1 – Layer I & II DiagramDiagram

Images from Peter Noll MPEG Digital Audio Coding Standards

MPEG1 – Layer IIIMPEG1 – Layer III

• Time Frequency MappingTime Frequency Mapping Switched Hybrid Filter BankSwitched Hybrid Filter Bank 32 sub-bands further sub-divided using a32 sub-bands further sub-divided using a

6 or 18-point DCT6 or 18-point DCT

• Psychoacoustic ModelPsychoacoustic Model Variable FFTVariable FFT Tonal & Noise MaskingTonal & Noise Masking

• QuantizerQuantizer Non-uniform Scale FactorsNon-uniform Scale Factors Huffman Coding, Bit Reservoir, & Iterative Huffman Coding, Bit Reservoir, & Iterative

AnalysisAnalysis

MPEG1 – Layer III DiagramMPEG1 – Layer III Diagram

Images from Peter Noll MPEG Digital Audio Coding Standards

MPEG2 – General OverviewMPEG2 – General Overview

• 5.1 Channel Support5.1 Channel Support

• Advanced Audio Coding (AAC)Advanced Audio Coding (AAC) Optional PreprocessingOptional Preprocessing Bit-stream FormatterBit-stream Formatter Prediction – helps to optimize quantizerPrediction – helps to optimize quantizer Noiseless CodingNoiseless Coding 3 Profiles3 Profiles

• Main – Variable length DCT, noiseless coding, etc.Main – Variable length DCT, noiseless coding, etc.

• Low Complexity – No temporal noise shaping & time Low Complexity – No temporal noise shaping & time domain predictiondomain prediction

• Sampling Rate Scalability – preprocessor allows for Sampling Rate Scalability – preprocessor allows for sampling rates of 6, 12, 18, & 24 KHzsampling rates of 6, 12, 18, & 24 KHz

MPEG4 - General OverviewMPEG4 - General Overview

• Consists of all previous MPEG iterationsConsists of all previous MPEG iterations

• Uses 3 Core CodersUses 3 Core CodersParametric coding for low bit rate speechParametric coding for low bit rate speechAnalysis-by-synthesis for medium bit ratesAnalysis-by-synthesis for medium bit ratesSub-band/Transform coding for high bit ratesSub-band/Transform coding for high bit rates

• Low Delay (LD) Encoding / DecodingLow Delay (LD) Encoding / Decoding

• Quality ScalabilityQuality Scalability

MPEG 4 - DiagramMPEG 4 - Diagram

Applications & Sound Applications & Sound Samples Samples • ApplicationsApplications

AVI2MP.EXEAVI2MP.EXE LAMEwin32LAMEwin32 Nero MPEG4 AACNero MPEG4 AAC GoldwaveGoldwave

• HardwareHardware Pentium III – 1.0 GHzPentium III – 1.0 GHz 512MB RAM512MB RAM Win2K SP3Win2K SP3

• Sound SamplesSound Samples PCM 16-bit Stereo 44.1 PCM 16-bit Stereo 44.1

KHzKHz• Clubbed to Death Clubbed to Death

(Kurayamino Mix) – Rob D(Kurayamino Mix) – Rob D

• Man Who Sold The World - Man Who Sold The World - NirvanaNirvana

PCM 8-bit Mono 44.1KhzPCM 8-bit Mono 44.1Khz• Voice SampleVoice Sample

Results – File size VS BitrateResults – File size VS Bitrate

Sample 2File Size VS Bitrate

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1,000,000.00

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32 48 56 64 80 96 112 128 160 192

Bitrate (kbps)

Sample 3File Size VS Bitrate

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16 24 32 48 56 64 80 96

Bitrate (kbps)

Results – Encode Time VS Results – Encode Time VS BitrateBitrate

Sample 1Encode Time VS Bitrate

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Sample 2Encode Time VS Bitrate

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Results – Quality VS BitrateResults – Quality VS Bitrate

Sample 2Quality VS Bitrate

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Sample 3Quality VS Bitrate

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Bitrate (kbps)

Sample SoundsSample Sounds

• Music SampleMusic Sample Original SoundOriginal Sound Sample 2 Play listSample 2 Play list S2-M4LT-064SS2-M4LT-064S S2-M4LT-080SS2-M4LT-080S S2-M4LT-096SS2-M4LT-096S

• Voice SampleVoice Sample Original SoundOriginal Sound Sample 3 Play listSample 3 Play list S3-M4LT-016MS3-M4LT-016M S3-M4LT-024MS3-M4LT-024M S3-M4LT-032MS3-M4LT-032M

Sample Waveforms – S2-64Sample Waveforms – S2-64

Sample Waveforms – S2-Sample Waveforms – S2-128128

Sample Waveforms – S3-64Sample Waveforms – S3-64

Sample Waveforms – S3-96Sample Waveforms – S3-96

SummarySummary

• MPEG1 – Layers I, II have limited options & MPEG1 – Layers I, II have limited options & are not size versus quality efficientare not size versus quality efficient

• MPEG1 – Layer III offers excellent quality MPEG1 – Layer III offers excellent quality at low rates but has large overheadat low rates but has large overhead

• MPEG2 – Much more comprehensiveMPEG2 – Much more comprehensive

• MPEG4 – Encompasses all previous MPEG4 – Encompasses all previous iterations & has new capabilities to iterations & has new capabilities to increase its lifespanincrease its lifespan