Audio Coding Team Member: ChungMing Yan, Chun Tong

Overview Mp3, AAC, Ogg Vorbis Technical specifications Test Results Sample clips Conclusion

Mp3 MPEG1 Layer 3 Audio Coding A research project in EUREKA Digital Audio Broadcasting (DAB) in 1987 A power of data reduction algorithm Standardized as ISO-MPEG Audio-Layer 3

Mp3 (Continued) Pros: Fast Decoding Excellent hardware support ISO standard Cons: Quality varies widely between encoders Even at highest quality, quality still suffers

Mp3 (Continue) Bit Rate: Average 128 kbps or 192 kbps Sampling Frequency: 16-24KHz (MPEG2 Layer 3) 32-48KHz (MPEG1 Layer 3) Parameters: Birate: 1. CBR (Constant Bitrate) 2. VBR (Variable Bitrate) 3. ABR (Average Bitrate)

Mp3 (Continue) Compression Techniques Huffman coding Non-linear quantization M/S Matrixing (Mid/side matrixing) Intensity stereo MDCT

Mp3 (Continue) Encoders: Lame, Audio Catalysis Decoders: Winamp, Window Media Player, etc.

AAC MPEG2/MPEG4 Advanced Audio Coding Developed by MPEG group (Dolby, Frauhofer, AT&T, Sony…etc) More over of mp3

AAC (Continued) Pros: Competitive at low and mid bitrates against other formats Decoders/Encoders work on all platforms Cons: All high-quality implementations of AAC encoding are non-free and closed source. Relatively CPU intensive

AAC (Continue) Bit Rate: 96 kbps, 128kbps, 196kbps Sampling Frequency: 48 full-bandwidth (up to 96 KHz) Low Frequency Enhancement (LFE to 120 KHz)

AAC (Continue) Profiles LC (Low Complexity) Main Main LTP

AAC (Continue) Compression techniques Huffman coding Non-linear quantization and scaling Vector quantization M/S matrixing (middle/side channels) for high bitrates Intensity stereo for low bitrates TNS (temporal noise shaping) LTP(MPEG4 profile 2, reduce redundancy in successive frames) MDCT PNS (perceptual noise shaping)

AAC (Continue) Encoders: Psytel AacEnc, Nero Decoders: Winamp (with an AAC plug- in), QuickTime 6

Ogg Vorbis Open source project Free, open, unpatented from other audio coding format

Ogg Vorbis (Continue) Pros: Open source and patent free No loyalties even in commercial products Cons: No commercial hardware players High bitrates not fully tuned

Ogg Vorbis (Continue) Bit rate: ~64kbps Sampling Frequency: From 8 KHz (telephony) to 192 KHz (Digital Masters)

Ogg Vorbis (Continued) Compression techniques Huffman coding MDCT (Cosine + Sine) Wavelet in Vorbis II to improve quality

Ogg Vorbis (Continue) Encoders: Besweet, OggDrop Decoders: Winamp (with an Ogg Vorbis plug-in)

Test Result Three music clip used Orchestra Music with voice Voice only Different bitrate setting (switches) High bitrate Medium variable bitrate Low bitrate Additional switches (voice, pns)

Sample clips Wav Mp3 Ogg AAC

filesizes mp3: track 1track 2track 3 original2470KB2587KB318KB cbr 256(160 voice) r3mix (96) abr abr /60 aac: track 1track 2track 3 original2470KB2587KB318KB cbr abr abr 48(tape, 40-59) cbr cbr 32 resampled ogg: track 1track 2track 3 original2470KB2587KB318KB cbr 256/ abr 96/ abr 48/ abr 32-the encoder cannot encode lower bitrate

Switches used Mp3 GUI automatically writes the proper command line CBR "c:\EE3414\lame\lame.exe" -m s -b 256 -k "C:\EE3414\input.wav" "C:\EE3414\output.mp3“ r3mix - "c:\EE3414\lame\lame.exe" --nspsytune --vbr-mtrh -V1 -mj -h -b96 --lowpass athtype 3 --ns-sfb21 2 -Z --scale X0 "C:\EE3414\input.wav" "C:\EE3414\output.mp3" abr 48 - "c:\EE3414\lame\lame.exe" --abr 48 -b 32 -B 320/160 "C:\EE3414\input.wav“ "C:\EE3414\output.mp3“ abr 32 - "c:\EE3414\lame\lame.exe" --abr 32 -b 32 -B 320/160 "C:\EE3414\input.wav" "C:\EE3414\output.mp3" abr 32 voice - "c:\EE3414\lame\lame.exe" --voice --abr 32 -b 32 -B 160 "C:\EE3414\voice.wav" "C:\EE3414\voice(abr32-voice).mp3"

Switches used (Continued) AAC cbr 256 -production -low_ath -profile 0 -br 256 abr 96 -production -profile 0 -br 96 –vbrhi abr 48-tape abr 32-br 32 abr 32-br 32 -resample 22050

Switches used (continued) Ogg Vorbis Lacking control parameters besides “quality” cbr 256 GUI quality set to 8 abr 96GUI quality set to 2 abr 48GUI quality set to -1 abr 32such bitrate is not possible with given tools even with manual bitrate tweaking

Conclusion ACC = Ogg > MP3 There are very little differences, very hard to tell Depends on application Alternative Audio Coding Lossless encoding Monkey audio Speech specific Speez

Future research or improvements As technology improves, there will be newer coding schemes to be examined More extensive research of the parameters and encoding procedures Matlab waveform analysis (object analysis) Alternative Implementation

Resources Team website