Transcript Chapter 15

Chapter 15
Recording and Editing Sound
Getting Started
• In this Chapter, you will learn:
− How sound capability enhances your PC
− How your PC records, stores, and plays digital
sound
− How speech synthesis works
− What you should know about MIDI
− What is ripping
− About Hardware: Sound devices
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How does sound capability
enhance by PC
• Sound adds a new dimension to your PC
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Beeps and sounds provide feedback as you use your PC
Music lovers can listen to sample tracks
Children can listen to stories
Visually impaired individuals can have the screen contents read to
them
• Computers work with two general categories of sound
– Digitized sound is a recording of real sound converted into electronic
signals
– Synthesized sound has not been recorded from a live source, but
instead has been generated by a machine
• Each sound category has unique characteristics and
applications
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How does my PC record, store, and
play digital sound?
• To digitally capture sound, you need a microphone and sound
software
• A sound wave provides information about a sound
– Height of wave indicates volume, called amplitude
– Time between wave peaks indicates the sound’s frequency
• To digitally store a sound wave, your PC periodically records a
sample of the wave’s amplitude as a binary number
– Sampling rates are measured in kHz (kilohertz), where 1 kHz is 1,000
samples per second
– For human voice, 11 kHz works fairly well. For music, 22 kHz to 44 kHz
is required
– Digital sound files that have not been compressed are big
– WAV is a popular uncompressed audio file format
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How does speech synthesis work?
• Machines produce sound that resembles the spoken word
through speech synthesis
– Most speech synthesizers string together basic sounds called
phonemes
• Speech synthesizer typically includes text-to-speech software
and synthesizing hardware
– Text-to-speech software examines the text on a PC and breaks it down
into a series of sounds that can be output
– Synthesizing software consists of electronic circuitry that can generate
speech or musical sounds
• Unlike digitized speech, synthesized speech can theoretically
produce any words or phrases
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What should I know about MIDI?
• MIDI (musical instrumental digital interface) specifies a
standard way to store music data
– MIDI files contain instructions, called MIDI messages, for synthesizing
music based on pitch, volume, and duration of each note made by
each instrument
– MIDI is suitable for instrumental music, but not for vocals
– MIDI’s advantage lies in its ability to store lengthy musical sequences
in a small file
• Use sequencer software to capture the musical themes from a
MIDI instrument or enter the notes on a musical staff
• Edit your composition by assigning notes to instruments,
adding harmony, and inserting percussion
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What should I know about MIDI?
Composing MIDI Music
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What is ripping?
• Ripping is slang for importing tracks from a CD or DVD to your
computer’s hard disk
– Technical term for ripping is digital audio extraction
– Ripping is handy when moving files between PCs and devices
• Music file formats
– CD-DA (Compact Disc Digital Audio) format for music on CDs
– Music from CDs is usually compressed into: MP3, AAC (Advanced
Audio Coding), and WMA (Windows Media Audio)
• Many software tools for ripping CD tracks are available
• In the U.S., ripping music for personal use is controversial
since it is done without the artist’s permission
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What is ripping?
Ripping music to a CD using iTunes software
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Hardware: Sound devices
• Most PCs today include a basic audio system with a
sound card, speakers, and possibly a microphone
• A sound card is a circuit board that typically plugs
into an expansion slot on your PC
− Provides connectors for a microphone, speakers or
headphones
− Provides a joystick port that doubles as a port for MIDI
instruments
• Basic sound card is adequate for playing games,
business software, and Web browsing
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Hardware: Sound devices
The sound card is the basic building block
of your PC’s audio system
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Hardware: Sound devices
• Digitized sound
− Sound card reproduces the digital samples in the sound
file
− Sound quality depends on several factors, the most basic
being frequency response. Frequency response is the
range of notes it can produce
• MIDI music
− Sound card receives messages from a MIDI file
− Wavetable synthesis generates music by patching
together a set of sounds (patch set) prerecorded as
individual notes from actual instruments
− 256-voice wavetable produces better quality sound than
a 64-voice wavetable
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Hardware: Sound devices
• Sound card outputs sound to speakers or headphones
− New technologies include surround sound, 3-D sound, and
environmental sound
• Speakers
− Speakers cannot improve sound quality, but cheap speakers
can degrade it
− Your speaker quality level should match the quality level of
your sound card
− Most speaker systems include two speaker units
− Higher end systems may also include a subwoofer to
produce enhanced bass sound
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Hardware: Sound devices
• Microphones
− Sound card receives input from a microphone or MIDI
device
− For better sound quality choose a good-quality “mic”
• Portable audio player
− Pocket-sized, battery-powered device that stores digital
music
− Transfer music from your PC or buy songs online
− Connect to headphones or stereo system
− Supports a variety of compressed audio formats
− Some can also play videos and e-books
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Can I copy it?
• What do you think?
– When you purchase a music CD, do you believe that
you have the right to convert it into any format
(such as cassette tape or MP3) for your own use?
– Do you think the Digital Millennium Copyright Act
should be revised to allow people to circumvent
DRM for music that has been purchased
legitimately?
– Have you ever been prevented from copying music
by some type of DRM technology?
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Chapter Summary
• You should now :
− Know how sound capability enhances your PC
− Know how your PC records, stores, and plays
digital sound
− Understand how speech synthesis works
− Know about MIDI
− Understand ripping
− Understand sound devices
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