Digital Music and Audio

Sound

• Sound is a disturbance of mechanical energy that propagates through matter (like air) as a longitudinal wave and impacts the ear drum.

Sound Waves

• A sound wave is measured in amplitude (loudness in decibels dB) and frequency (pitch in Hz).

am

plit

ud

e

time

loud soft

low

high

• Humans can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range)• Most human speech communication takes place between 200 and 8,000 Hz• Prolonged exposure to a sound pressure level exceeding 85 dB can permanently damage the ear• Sound levels in excess of 130 dB are more than the human ear can safely withstand and can result in serious pain and

permanent damage.

oscilloscope demo

Sound Wave

seconds

Zoomed Sound Wave

milliseconds

millseconds

Digitizing Sound

• The sound wave is measured or “sampled” at regular time intervals to transform it into a list of numbers.

.28

0

-.45-.5

.08

.27

.08

-.1

Sampling Rates

• The amount of times per second that a sound wave is measured (sampled), measured in Hz.– 8,000 Hz - telephone– 22,050 Hz - FM quality– 44,100 Hz - CD quality– 192,000 Hz –HD-DVD

Bit Rate

• The combination of the sampling rate, amount of bits used with each sample, and mono vs. stereo determines the total number of bits processed per second, or the bit rate. The higher the bit rate the higher the quality of sound.– 4 kbit/s — minimum necessary for recognizable speech– 8 kbit/s — telephone quality – 32 kbit/s —AM radio quality – 96 kbit/s — FM radio quality – 128 - 160 kbit/s - Decent quality– 192 kbit/s — Good quality– 224 - 320 kbit/s — High quality, nearly lossless quality – 500 kbit/s–1 Mbit/s — lossless audio – 1411 kbit/s — PCM sound format of Compact Disc Digital Audio

Calculating CD Quality Bit Rate

• 16 bits are used for each sample value

• x 44,100 samples per second (CD)

• x 2 for stereo

• = 1,411,200 bits per second

a three minute CD song uses 1,411,200 x 180 (seconds)= 254,016,000 bits/8 = 31,752,000 bytes or about 31 MB.

The main uncompressed audio format is PCM. It is used on CDs and stored as a .wav on Windows or as .aiff on Mac OS

Digital audio compression: MP3• MPEG-1 Audio Layer 3, more commonly referred to as MP3, is

a popular digital audio encoding and lossy* compression format and algorithm, designed to greatly reduce the amount of data required to represent audio, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners.

• MP3 uses psychoacoustic models to discard components less audible to human hearing, and recording the remaining information in an efficient manner - typically 1/10th the size of the original uncompressed audio file.

• LAME produces the highest-quality MP3 files for bitrates greater or equal to 128 kbit/s.

*Lossless compression allows the original sound recording to be rebuilt from the compressed file, lossy loses some of the original sound characteristics. Lossy compressed files can never be returned to the original recording quality.

Newer Compressed Audio Formats: AAC & MWA

• Apple’s Advanced Audio Coding (AAC, or .m4a) format achieves better quality sound than MP3 for the same compression level or smaller file sizes for the same quality audio.

• Microsoft’s Windows Media Audio (WMA or .wma) format reduces file size but does not necessarily improve sound quality.– WMA 10 Pro (Media Player 11) is much better

than plain WMA

Review

• How is music digitized?• What is sampling rate?• As the sampling rate increases what happens

to the sound quality?• What is the sampling rate for CD quality

sound?• What is bit rate?• How is bit rate calculated for CD quality

sound?

Review

• How do MP3 files compare in quality and size to CD audio?

• What is Psychoacoustic and how does it relate to MP3?

• What are lossless and lossy in regards to audio compression?

• What is Microsoft’s preferred audio file format?

• What is Apple’s preferred audio file format?

Players, Services, Formats & DRM

Digital Rights Management (DRM)

• DRM provides a way to control if and how many times a digital music file can be copied.– Fairplay: Apple’s DRM technology used in m4p

files.– Janus: Microsoft’s DRM technology used in wma

files (wma-drm 9.0).– Zune wma-drm 9.1: Microsofts new DRM for

Zune not compatible with Janus.

http://en.wikipedia.org/wiki/Digital_rights_management

Online Music Distribution

• Wma drm 9.0 Online Stores– AOL Music Now – Yahoo! Music Unlimited – Musicmatch – Napster – Rhapsody To Go – Ruckus – Sony Music Store– URGE – Virgin Digital – Tesco Downloads

• M4P Stores– iTunes

• No DRM Stores– www.eMusic.com

The public’s reaction to DRM…

• Wma drm 9.1 Stores– Zune

Audio File Formats & Playerswav aiff mp3 aac

(m4a)aac(m4p)

wma wma(drm 9.0)

wma(drm 9.1)

iPod X X X X X

Zen X X X X

Zune X X X X

http://en.wikipedia.org/wiki/Audio_file_format

Ripping CD’s & Encoding

• Ripping: Transferring Music from CD to hard drive

• Encoding: Changing the format of a music file

• Demo

Audio File Formats & Serviceswav aiff mp3 aac

(m4a)aac(m4p)

wma wma(drm 9.0)

wma(drm 9.1)

iPod X X X X X

Zen X X X X

Zune X X X X

iTunes X

Napster X

Zune X

Restrictions: Fairplay & iTunes

• FairPlay will allow a protected track to be used in the following ways:– The protected track may be copied to any number

of iPod portable music players. – The protected track may be played on up to five

authorized computers simultaneously. – The protected track may be copied to a standard

Audio CD any number of times. • The resulting CD has no DRM and may be ripped,

encoded and played back like any other CD. – A particular playlist within iTunes containing a

protected track can be copied to a CD only up to seven times before the playlist must be changed.

Demo iTunes

Restrictions: Janus & Napster

• Monthly Subscription: – $10 per month to download and stream an

unlimited amount of music while subscribed to the service.

– $5 per month to use the music on “PlaysForSure” portable device.

• $.99 song purchases– Unlimited burns of individual tracks.– Unlimited transfers to Napster compatible portable

devices. – Copy your music to three computers.

Demo Napster

Restrictions: WMA DRM 9.1, Zune

• Zune Marketplace Subscription$14.99/month– Access millions of songs from 3 PC– Transfer to Zune player– No burning to disk

• Purchase songs with Microsoft Points, 400 for $5 = 79 points per song = $0.99

• Wirelessly share music with other Zunes. Shared songs last three days or three plays.

Demo: Zune

Review

• What is the purpose of DRM?• What are the three popular forms of DRM in

use today?• Which DRM is supported by the most online

music services?• What portable player would you buy if you

wanted to use Napster? • How about iTunes or Zune?• Would you consider the online music industry

to be well organized?

Digital Music Options

Online Music

• Pay Per Track– www.itunes.com

• Monthly Subscription– www.napster.com

• Internet Radio– www.live365.com – www.wmnf.org

• Free Services– www.pandora.com

Portable MP3 Players

• www.cnet.com > MP3• Portable players selection based on

– compatibility– capacity (flash or microdrive)– ease of use

• Selecting headphones (www.cnet.com)

Podcasts

• www.podcast.net• http://www.ipodder.org • iTunes• Podcast Software

– http://juicereceiver.sourceforge.net/

• Making Podcasts– GarageBand (demo)– http://www.podcastingnews.com/topics/Podcasting

_Software.html

RSS (Really Simple Syndication) is a family of web feed formats used to publish frequently updated digital content, such as blogs, news feeds or podcasts.

Home/Auto MP3 Players

• www.cnet.com > Home Audio > Network Audio Player

• iPod Complimentary Speaker Systems

• iPod Compatible Auto Sound Systems

• CD/MP3 Players

Cell Phone Music Service

• http://getitnow.vzwshop.com

• www.cingular.com/learn/music-video/music-center.jsp

Satellite Radio

• Sirius vs. XM: Choice based on– Price ($12.95/month)– Quality of Service– Quality of Receivers– Programming

Digital Radio

• www.hdradio.com

Summary: Music Devices

  Home Office Auto OnFoot

AM/FM Radio X X X X

HD Radio X X X  

Satellite Radio X X X X

CD Player (CD-R MP3 Capable) X X X  

Television X      

Personal Computer X X    

Network Audio System X      

Portable Player (iPod) X X X X

Portable Player Speaker System X X X  

Cell Phone X X X X

Summary: Music Suppliers  Price Streamed On Demand User Owned Legal Availability Programming Total

Internet Music Subscription (Napster) 5 10 10 10 10 9 9 63

Cell Phone Music Service 3 10 10 10 10 9 5 57

Internet Pay Per Tune Only (iTunes) 5 0 10 10 10 10 9 54

Podcasts 10 0 10 10 10 10 4 54

File Sharing Networks 10 0 10 10 0 10 10 50

CD Vendors 0 0 10 10 10 5 10 45

CD Rip and Burn 10 0 10 10 0 5 10 45

Internet Radio 10 10 0 0 10 4 5 39

Satellite Radio 5 10 0 0 10 8 5 38

HD Radio Stations 10 10 0 0 10 3 4 37

Radio Stations 10 10 0 0 10 3 3 36

Cable TV 8 10 0 0 10 2 2 32