MTD2 class 9

In class

• Review and discuss rough movie edits.
• Digital Theory 2
  • Listen to Beethoven exmaples (Sample Rate and Bit Depth)
  • Discuss Digital Errors
  • Look at sampling circuit
• Quiz Three Next week digital thoery 1 and 2 and chapter 3 from Sound Design for Interactive Multimedia

More Digital Theory

More digital theory…

Quantization

discrete levels based on the number of bits

Analog is like a bucket of water while digital is like a bucket of ball bearings. Analog has an infinite resolution while a digital system can only resolve thins to finite values.

"...if sheets of typing paper were stacked 22 feet, a single sheet of paper would represent one quatization level in a 16-bit system. In a 20-bit system, the stack would reach 349 feet. In a 24-bit system, the stack would tower 5592 feet in height - over a mile high." -Principals of Digital Audio, Ken C. Pohlmann McGraw Hill

1. The more bits you have the more dynamic range you have. Each bit is equal to aporximately 6 more dB. 16 dB s about 120 dB of dynamic range.

Quantization error = the difference between the actual analog value and the quantized digital value.

===Dither===- noise added to signal

dither.gif (29407 bytes)

addition of a small amount of white noise to the signal to reduce signal-to-error distortion ...also aid in processing and bit depth conversion... see dither article

Dither, Article Sampling Frequency/Aliasing

sampling1.gif (39564 bytes)

Nyquest Theorem -- The sampling frequency determines the high frequency limit.

Sampling frequency = discrete time frequency of the sampler

44.1 kHz = CD audio

square wave @ 20KHz won't make it w/ a 44.1 kHz sampler

Aliasing

Aliasing = error caused by under sampling -- cars wheels in movies

Need a brick wall filter at the imput of the samplig circuit with a cut off frequency of 1/2 the smapling rate

Three types of digital errors

   * Quantization Error - Difference between actual analog value and quantized digital value
   * Aliasing - Undersampling
   * Jitter - Time errors 

Jitter

Error due to clock synchronization...More on this next time

Signal Flow

low pass filter (ideally a brick wall filter) --> AD Converter --> DA converter --> low pass filter

pcm.gif (23735 bytes)

MORE

READ dither Article

http://www.digido.com/ditheressay.html

READ Jitter Article

http://www.digido.com/jitteressay.html

Homework

   * Work on Audio for Storyboard movie
   * Post another version of the exported movie
   * Quiz Three Next week