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
- 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