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 1 track 2 track 3 original 2470KB 2587KB 318KB cbr 256 (160 voice) 451 472 291 r3mix (96) 283 381 174 abr 48 83 91 90 abr 32 54 60 60/60

aac: track 1 track 2 track 3 original 2470KB 2587KB 318KB cbr 256 446 467 232 abr 96 217 231 145 abr 48 (tape, 40-59) 104 102 90 cbr 32 57 60.4 59.2 cbr 32 resampled 56.9 59.8 53.6

ogg: track 1 track 2 track 3 original 2470KB 2587KB 318KB cbr 256 /8 389 427 304 abr 96 /2 140 167 131 abr 48 /-1 63.9 98.7 80.7 abr 32 -the encoder cannot encode lower bitrate

Switches used Mp3

• GUI automatically writes the proper command line• CBR 256 - "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

19.5 --athtype 3 --ns-sfb21 2 -Z --scale 0.98 -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 96 GUI quality set to 2• abr 48 GUI quality set to -1• abr 32 such 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 http://www.audiocoding.com http://lame.sourceforge.net http://www.vorbis.com

Team website• http://chii.servehttp.com:10240/ee3414