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W.A.V.S. Compression Alex Chen Nader Shehad Aamir Virani Erik Welsh.

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Presentation on theme: "W.A.V.S. Compression Alex Chen Nader Shehad Aamir Virani Erik Welsh."— Presentation transcript:


2 W.A.V.S. Compression Alex Chen Nader Shehad Aamir Virani Erik Welsh

3 Overview Approach Psychoacoustic Modeling Filter Banks Quantization Demonstration Results Further Research

4 Approach Filter Banks Psychoacoustic Model Quantization Inverse Quantization Reconstruction Filter Banks Encoding: Input Encoded Signal Decoding: Encoded Signal Output

5 Psychoacoustic Model Based on studies that show hearing capabilities affected by: Environment Limitations of human auditory system Used to eliminate portions of signal average human wont hear Two key properties: Absolute threshold of hearing Auditory masking

6 Absolute Threshold of Hearing Experiment: Plot audible threshold of tone Observations: Auditory system sensitive to some frequencies Frequencies within critical bandwidth treated similarly Basis for Bark scale

7 Auditory Masking Tones and noise drown out less powerful sounds Affect neighboring frequencies Affect critical bandwidth Effects add to produce overall masking threshold Mask quantization

8 Filter Banks Theory Array of bandpass filters Break up signal into frequency subbands Allows for variable coding scheme

9 Analysis and Synthesis Banks 1) Analysis filters divide up the signal 2) Down-sample 3) Quantize 4) Up-sample 5) Synthesis filters remove distortions 6) Reconstruct the signal

10 Filter Bank Design Phase Tradeoff between fine and coarse frequency resolution Piccolo vs. Castanets Non-stationary signals We used non-adaptive approach

11 Filter Bank Implementation We used Cosine Modulated PR (perfect reconstruction) filter banks with 32 filters each Output is a delayed version of the input (linear phase) Distortion arises from quantization only

12 Quantization Two types Narrow-band Current input Overhead cost Full-range Independent of current input No overhead Sampled Input Quantized Version Reconstructed Input

13 Quantization Narrow Band More accurate Lower compression ratio Full-Range Less accurate Higher compression ratio Using 3-bit Quantization Input: -.4 -.22.14.4 Levels: 1 3 6 8 Recon.: -.4 -.2.1.3 Total Error:.16 Input: -.4 -.22.14.4 Output: 3 4 6 7 Recon: -.5 -.25.25.50 Total Error:.34

14 Demonstration Sine wave Full range Narrow range Chime 8-bit Full range Narrow range Percussion Full Range Narrow Range Modern 8-bit Full Range Narrow Range

15 Sine Wave (time) Full-Range QuantizationNarrow Quantization

16 Sine Wave (freq) Full-Range QuantizationNarrow Quantization

17 Sine Wave (freq error) Full-Range QuantizationNarrow Quantization

18 Modern (time) Full-Range QuantizationNarrow Quantization

19 Modern (freq) Full-Range QuantizationNarrow Quantization

20 Modern (freq error) Full-Range QuantizationNarrow Quantization

21 Results Full Range: Smallest File, Worst Sound Quality Narrow Range: Better Sound Quality, Larger File MP3: Industry Standard

22 Further Research Filter Banks Wavelets Dynamic Frequency Ranges Better Psychoacoustic Model Tone Designation Pre- and Post- Echo Bit Allocation Writing a File

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