MTD2 class 12

From IAM MediaWiki Create Change
Jump to: navigation, search


  • Lecture on Compression
  • Import Export Tutorial

audio compression

  • Compression
  • Psychoacoustics
  • MPEG Codec

Compression

Second Law of Thermodynamics Entropy is always increasing.


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 http://en.wikipedia.org/wiki/Category:Compression_algorithms

Lossless_compression_algorithms

Lossy_compression_algorithms

Lossless Huffman and Run length

Huffman

Huffman algorithm uses the probability of occurrence to code messages.

Huffman Encoding WikiPedia

Morse code is simple entropy encoding similar to the huffman algorithm. (.) = e them most common letter (--..) = z a seldom used letter. Practical Huffman coding

Run-length_encoding Run Length Encoding encoded 6666 66666 as 86 or 8 sixes

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.

Masking Examples http://iam.colum.edu/MTD2/masking/

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 Sub band 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 bit depth. 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

Video Compression

Video on a computer is usually compressed because it is large and we want to reduce the Data Rate.

Homework

  • Continue work on animation in flash.
  • Practice importing animations in flash and importing to Premiere
  • Import Export Tutorial
  • Post another version with more animation

Links

  • Mpeg class notes MPEG.org