This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743,
Jennifer Burg PI, Jason Romney, Co-PI.
5 Chapter 5 Digitization ......................................................................1
5.1 Concepts ..................................................................................1
5.1.1 Analog Vs. Digital ................................................................1
5.1.2 Digitization .........................................................................3
5.1.2.1 Two Steps: Sampling and Quantization ............................ 3
5.1.2.2 Sampling and Aliasing .....................................................4
5.1.2.3 Bit Depth and Quantization Error ......................................6
5.1.2.4 Dynamic Range ..............................................................9
5.1.2.5 Audio Dithering and Noise Shaping .................................15
5.1.3 Audio Data Streams and Transmission Protocols .................... 16
5.1.4 Signal Path in an Audio Recording System ............................ 18
5.1.5 CPU and Hard Drive Considerations ......................................20
5.1.6 Digital Audio File Types .......................................................21
5.2 Applications ............................................................................25
5.2.1 Choosing an Appropriate Sampling Rate ............................... 25
5.2.2 Input Levels, Output Levels, and Dynamic Range ................... 25
5.2.3 Latency and Buffers ...........................................................30
5.2.4 Word Clock .......................................................................33
5.3 Science, Mathematics, and Algorithms .......................................36
5.3.1 Reading and Writing Audio Files in MATLAB ........................... 36
5.3.2 Raw Audio Data in C++ ......................................................40
5.3.3 Reading and Writing Formatted Audio Files in C++ ................ 42
5.3.4 Mathematics and Algorithms for Aliasing ............................... 45
5.3.5 Simulating Sampling and Quantization in MATLAB .................. 48
5.3.6 Simulating Sampling and Quantization in C++ ....................... 48
5.3.7 The Mathematics of Dithering and Noise Shaping...................49
5.3.8 Algorithms for Audio Companding and Compression ............... 54
5.3.8.1 Mu-law Encoding .........................................................54
5.3.8.2 Psychoacoustics and Perceptual Encoding ........................ 58
5.3.8.3 MP3 and AAC Compression ............................................59
5.3.8.4 Lossless Audio Compression ..........................................69
5.4 References .............................................................................70
5 Chapter 5 Digitization
5.1 Concepts
5.1.1 Analog Vs. Digital
Today’s world of sound processing is quite different from what it was just a few decades ago. A
large portion of sound processing is now done by digital devices and software mixers,
dynamics processors, equalizers, and a whole host of tools that previously existed only as analog
hardware. This is not to say, however, that in all stages from capturing to playing sound is
now treated digitally. As it is captured, processed, and played back, an audio signal can be
transformed numerous times from analog-to-digital or digital-to-analog. A typical scenario for
Previous Page Next Page