Audio%20Coding

1
Audio Coding

• MPEG1 Layers I, II, III
• MPEG2
• MPEG4

Sherida Subrati Anthony Caliendo
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Overview

• Explanation of Codecs
• MPEG1 Layer I, II, III (Differences)
• MPEG2 Basic Overview
• MPEG4 Possible Applications
• Applications Sound Samples Used
• Results Explanation
• File Size, Bitrate, Quality
• Waveform Comparison
• Summary Questions

3
Sub-Band Coding Overview

• Size of sub-bands varies
• Varying application of psychoacoustic model

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MPEG1 Layer I II

• Time Frequency Mapping
• Polyphase Filter Bank
• 32 Equal Bands
• Psychoacoustic Model
• 512-point FFT 1024-point FFT respectively
• Tonal Noise Masking
• Quantizer
• Scale Factor 6 bits
• Layer II Allows 3 successive scale factors
  uses 1-3 depending on how much they differ

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MPEG1 Layer I II Diagram
Images from Peter Noll MPEG Digital Audio Coding
Standards
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MPEG1 Layer III

• Time Frequency Mapping
• Switched Hybrid Filter Bank
• 32 sub-bands further sub-divided using a6 or
  18-point DCT
• Psychoacoustic Model
• Variable FFT
• Tonal Noise Masking
• Quantizer
• Non-uniform Scale Factors
• Huffman Coding, Bit Reservoir, Iterative
  Analysis

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MPEG1 Layer III Diagram
Images from Peter Noll MPEG Digital Audio Coding
Standards
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MPEG2 General Overview

• 5.1 Channel Support
• Advanced Audio Coding (AAC)
• Optional Preprocessing
• Bit-stream Formatter
• Prediction helps to optimize quantizer
• Noiseless Coding
• 3 Profiles
• Main Variable length DCT, noiseless coding,
  etc.
• Low Complexity No temporal noise shaping time
  domain prediction
• Sampling Rate Scalability preprocessor allows
  for sampling rates of 6, 12, 18, 24 KHz

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MPEG4 - General Overview

• Consists of all previous MPEG iterations
• Uses 3 Core Coders
• Parametric coding for low bit rate speech
• Analysis-by-synthesis for medium bit rates
• Sub-band/Transform coding for high bit rates
• Low Delay (LD) Encoding / Decoding
• Quality Scalability

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MPEG 4 - Diagram
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Applications Sound Samples

• Applications
• AVI2MP.EXE
• LAMEwin32
• Nero MPEG4 AAC
• Goldwave
• Hardware
• Pentium III 1.0 GHz
• 512MB RAM
• Win2K SP3

• Sound Samples
• PCM 16-bit Stereo 44.1 KHz
• Clubbed to Death (Kurayamino Mix) Rob D
• Man Who Sold The World - Nirvana
• PCM 8-bit Mono 44.1Khz
• Voice Sample

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Results File size VS Bitrate
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Results Encode Time VS Bitrate
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Results Quality VS Bitrate
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Sample Sounds

• Music Sample
• Original Sound
• Sample 2 Play list
• S2-M4LT-064S
• S2-M4LT-080S
• S2-M4LT-096S

• Voice Sample
• Original Sound
• Sample 3 Play list
• S3-M4LT-016M
• S3-M4LT-024M
• S3-M4LT-032M

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Sample Waveforms S2-64
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Sample Waveforms S2-128
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Sample Waveforms S3-64
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Sample Waveforms S3-96
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Summary

• MPEG1 Layers I, II have limited options are
  not size versus quality efficient
• MPEG1 Layer III offers excellent quality at low
  rates but has large overhead
• MPEG2 Much more comprehensive
• MPEG4 Encompasses all previous iterations has
  new capabilities to increase its lifespan