Analog to Digital Conversion of Sound Adam White

Conversion Of Sound (ADC) Digital Audio Workstation(DAW)

Basics of Signal Conversion Sender ADC - converts an input analog voltage to a digital number proportional to the magnitude of the voltage or current. - Binary, Grays Code, 2’s complement Data Manipulation DAC Receiver

ADC Structures Binary – base 2 Grays Code 2’s Complement

Sampling The process of going from continuous time to discrete time sample rate Higher the sample rate = better quality, more storage What is the best sampling rate?

Nyquist’s Theorem the ADC's sampling rate must be at least twice the maximum bandwidth of the signal. The maximum bandwidth is called the Nyquist frequency. Aliasing

Resolution the number of bits used to represent the analog input signal. Higher the resolution, the more accurately the signal is replicated. Higher resolution reduces the quantization error.

Resolution eight bits resolution means it can hold values from 0 to 255 (2^8 = 256) -Example: Phone Systems 16 bits resolution, this means it can hold values from 0 to 65,535 (2^16 = 65,536). - Example: Audio CD’s 24 bit resolution is used for high end audio applications.

Quantization Error the difference between the actual analog input and the digital representation of that value Unavoidable Happens from rounding or truncation Is ok for phone systems

Non-Linear Error physical imperfections Output deviates from the linear function of their input Can be prevented by testing Either best fit straight line or line between end points

ADC Designs Flash Successive approximation Ramp Counter Wilkensons ADC Integrated ADC Delta Coded ADC Pipeline ADC Time Interleaved ADC

Flash Efficient for small resolution Fast Only has 8 bits of resolution Disadvantage – lots of comparators

Ramp Counter uses a counter Records value when they are equal Very Slow Inefficent

Successive Approximation Based off of Binary Search Throws out half the values each iteration Better for larger resolution Most popular fast

C CODE

Digital Audio Workstation DAW is the combination of a Mac or PC, software, and ADC. ADC in DAW acts as a sound card Usually external to computer. Often rackmountable High end sound cards, fast CPUs, lots of RAM, Large hard drives.

Computer Based DAW Separate Computer, Software, Hardware More Prevalent today Cheaper Software controls the two hardware components and provides a user interface to allow for recording and editing.

Integrated DAW combines all of the necessary components such as computing power, software, analog to digital conversion, and a gui all in the same unit. More popular throughout the 1980’s and 1990’s As computing power increased and costs decreased, popularity of integrated systems dropped.

DAW allows the software to act like a mixer – Volume control – Panning – EQ – Effects – cut, copy, paste – Splicing tracks – Multi-track Recording – “forcast” tracks

History Created by Bob Ingebretsen and JimYoungber 1970 First available to consumers in 1987 by digidesign Digidesign was available to Macintosh users Originally called Sound Tools – later chaged to ProTools. First Windows DAW introduced by Soundscape Digital Technology (year)

Pro Tools Mac or Windows More popular among Mac Developed and designed by DigiDesign Must be used with a DigiDesign ADC M-powered can be used with M-audio interface First version sold for $6,000 Sold now for $495 to $1995 “Industry Standard”

Cubebase Created by Steinberg Windows or mac More popular for windows First released in 1989 $499

Open Source Audacity DEMO