Audio Coding MPEG1 Layers I, II, III MPEG2MPEG4 Sherida Subrati Anthony Caliendo

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

Sub-Band Coding Overview Size of sub- bands varies Size of sub- bands varies Varying application of psychoacoustic model Varying application of psychoacoustic model

MPEG1 – Layer I & II Time Frequency Mapping Time Frequency Mapping  Polyphase Filter Bank  32 Equal Bands Psychoacoustic Model Psychoacoustic Model  512-point FFT & 1024-point FFT respectively  Tonal & Noise Masking Quantizer Quantizer  Scale Factor: 6 bits  Layer II – Allows 3 successive scale factors & uses 1-3 depending on how much they differ

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

MPEG1 – Layer III Time Frequency Mapping Time Frequency Mapping  Switched Hybrid Filter Bank  32 sub-bands further sub-divided using a 6 or 18-point DCT Psychoacoustic Model Psychoacoustic Model  Variable FFT  Tonal & Noise Masking Quantizer Quantizer  Non-uniform Scale Factors  Huffman Coding, Bit Reservoir, & Iterative Analysis

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

MPEG2 – General Overview 5.1 Channel Support 5.1 Channel Support Advanced Audio Coding (AAC) 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. Main – Variable length DCT, noiseless coding, etc. Low Complexity – No temporal noise shaping & time domain prediction Low Complexity – No temporal noise shaping & time domain prediction Sampling Rate Scalability – preprocessor allows for sampling rates of 6, 12, 18, & 24 KHz Sampling Rate Scalability – preprocessor allows for sampling rates of 6, 12, 18, & 24 KHz

MPEG4 - General Overview Consists of all previous MPEG iterations Consists of all previous MPEG iterations Uses 3 Core Coders 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 Low Delay (LD) Encoding / Decoding Quality Scalability Quality Scalability

MPEG 4 - Diagram

Applications & Sound Samples Applications Applications  AVI2MP.EXE  LAMEwin32  Nero MPEG4 AAC  Goldwave Hardware Hardware  Pentium III – 1.0 GHz  512MB RAM  Win2K SP3 Sound Samples 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

Results – File size VS Bitrate

Results – Encode Time VS Bitrate

Results – Quality VS Bitrate

Sample Sounds Music Sample Music Sample  Original Sound Original Sound Original Sound  Sample 2 Play list Sample 2 Play list Sample 2 Play list  S2-M4LT-064S S2-M4LT-064S  S2-M4LT-080S S2-M4LT-080S  S2-M4LT-096S S2-M4LT-096S Voice Sample Voice Sample  Original Sound Original Sound  Sample 3 Play list Sample 3 Play list  S3-M4LT-016M S3-M4LT-016M  S3-M4LT-024M S3-M4LT-024M  S3-M4LT-032M S3-M4LT-032M

Sample Waveforms – S2-64

Sample Waveforms – S2-128

Sample Waveforms – S3-64

Sample Waveforms – S3-96

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