MTD2 class 12

   *  Lecture on Comression
   * Import Export Tutorial 

AudioCompression

   * Compression
   * Psychoacoustics
   * MPEG Codec 

Compression Types and Techniques

Entropy algorithms and A.I.C. algorithm information Content Entropy in Logic and the Theory of Algorithms Reducing redundancy decreases data rate increasing redundancy increases data rate.

lossy vs. lossless

Lossless Huffman and Runlength Huffman algorithm uses the probability of occurrence to code messages. Morse code is simple entorpy encoding similar to the huffman algorithm. (.) = e them most common letter (--..) = z a seldom used letter. Practical Huffman coding Run Length Encoding encoded 6666 66666 as 86 or 8 sixes

   * Cnet
   * "Run Length Encoding" 

Psychoacoustics The study of the way we hear sounds (what the brain interprets from what the ears pick up).

Aural masking is just as real as visual making. Such as temporary blindness do to bright or low light or something blocking your view.

Frequency Masking

Frequencies can become masked when they are about within about 1/3 octave frequency range and 4dB below the masking sound. Lower frequency sound better mask higher frequency sounds.

Temporal Masking

Temporal masking may also occur for about 25ms before and after the masking signal this is known as pre (if the sound before the masking signal is masked) and post (if the masker is after) masking. More Compression Subband coding

Reduction of quantization of non-essential frequency bands

Blocks of time-domain samples are split in separate filter bands. These filter bands are then run against Psychoacoustic models to determine necessary energy of each band. Bands that are masked may be discarded or be coded with reduced bitdepth. Transform coding

Similar to Subband coding except uses frequency coefficients to reduce bitdepth Frequency coefficients may be adaptive MPEG-1 Audio Motion Picture Experts Group ISO/IEC International Standard 11172 1992 Encoding for audio and video max bit rate 1.856 Mbps Adapted from MUSICAM (Masking-pattern Universal Subband Intergrated Coding and Multiplexing) MPEG-1 Layer I least complicated algorithm MPEG-1 Layer IIA DVD MPEG-1 Layer III most complicated algorithm

   * Fraunhofer http://www.iis.fhg.de/amm/techinf/layer3/index.html
   * http://www.mp3-tech.org/
   * Simple Mp3 

Video Compression Video Compression Compresson the digital video site Homework Start animation in flash. Practice emporting animations in flash and importing to Premiere Import Export Tutorial Links Mpeg class notes MPEG.org