Skills: Set sample size and rate in AudacityConcepts: analog versus digital data, analog to digital conversion, digital to analog conversion, sample rate, sample size, quality-file size trade off

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.

Recording and encoding analog data

Where does this topic fit?

• Internet concepts– Applications– Technology– Implications

• Internet skills– Application development– Content creation– User skills

Analog data

But, computers require digital data …

http://som.csudh.edu/fac/lpress/presentations/clocks/clocks.html

Which clock is digital? Analog?

A digital clock

00 0201 03 04 …

01.49

Analog to digital converter

Digital to analog converter

Recording and playing sound

Computer

10010110 (150)11001001 (201)11000111 (199)…

Computer

10010110 (150)11001001 (201)11000111 (199)…

Analog to digital converter

Digital to analog converter

Reading and adjusting temperature

Computer

10010110 (150)11001001 (201)11000111 (199)…

Computer

10010110 (150)11001001 (201)11000111 (199)…

Sensors for all sorts of things• Speed• Rate of flow• Pressure• Altitude• Acceleration• Motion• Rotation• Temperature• Light level• Sound• Compass direction• Blood pressure• Heart rate• And more …

The Internet of things

Sampling an analog signal

How can we improve the fit of the digital curve? (Hint: 2 ways)

What is the second thing we can increase? Hint: how did we increase the variety of colors in images or symbols in text?

1. Increase the sampling rate

00

11

10

01

000

010001

011100

110101

111

Two bits per sample

Three bits per sample

2. Increase the sample size

Finer voltage steps

Increase sample rate → quality ↑ file size ↑

Increase sample size → quality ↑ file size ↑

Recording tradeoffs

0 0 A

0 1 B

1 0 C

1 1 D

Text2-bits/character

Image1-bit/pixel

Sound2-bits/sample

Increase code bits → quality ↑ file size ↑

Edit > Preferences > Quality

Set default sample rate and size

Set sample rate and size

Analog Digital

What other real world phenomena can we sample and input to a computer?

Summary

Self-study questions

At a sampling rate of 8,000 16-bit mono samples per second, what would be the file size for a one minute recording?

How much larger would a stereo recording be?

How much larger would the file size be if we were to sample at 48,000 samples per second?

How much larger would the file size be if the samples were 32 bits each?

Resources

Wikipedia analog:http://en.wikipedia.org/wiki/Analog_signal

Wikipedia digital:http://en.wikipedia.org/wiki/Digital

A more detailed tutorial:http://www.planetoftunes.com/digiaudio/how_a_to_d.html