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