Digital sound works by sampling analog sound waves and representing them with numeric data. For audio CDs, sounds are sampled 44,100 times per second with 16-bit precision. Audio compression reduces file sizes by removing extraneous sounds. Digital audio is played back through sound cards and popular formats include MP3, WAV, and AIFF. MIDI files store musical instrument commands instead of sampled sound. Speech synthesis converts text to speech while recognition converts speech to text.

1. Chapter 8 Section A: Digital Sound

2. What is sound? Sounds are pressure waves of air, that pushes on your eardrum slightly, causing you to hear. Our ears are sensitive to these pressure waves, if there wasn't any air, we wouldn't be able to hear sounds. There's no sound in space.

3. What is sound? When you clap your hands, the air that was between your hands is pushed aside. This increases the air pressure in the space near your hands.

4. Chapter 8: Digital Media 4 What is Digital Audio? Digital representation of sound, in other words Music, speech and other sounds represented in binary format for use in digital devices.

5. Digital Audio Basics To digitally record sound, samples of the sound wave are collected at periodic intervals and stored as numeric data. Chapter 8: Digital Media 5

7. One thousand samples per second is expressed as 1,000 Hz (kilohertz).

8. The height of each sound sample can be saved as an 8-bit number for radio quality recordings or a 16-bit number for high-fidelity recordings.Sampling Size: number of bits in the digital representation of each sample.

10. An audio CD has a sample rate of 44,100 HZ (44.1 Khz), which means that a sample of the sound is taken 44,100 times per second.

11. An audio CD has a precision of 16-bits sample (bits per second), meaning that sixteen bits are used for each sample, for stereo you must take two 16-bit samples, requiring 32-bits for each sample.

14. Digital Audio Basics For CD-quality music at 44.1 kHz, one minute of music requires about 10 MB of storage, 45 minutes of music 450 MB. Chapter 8: Digital Media 10

15. Audio Compression Audio compression reduces the size of sound file by removing bits that represent extraneous noise and sounds that are beyond the frequencies of normal hearing. Advantage: a compressed file requires less storage space than an uncompressed file and can be transmitted faster over a network. Chapter 8: Digital Media 11

16. Chapter 8: Digital Media 12 Digital Audio Basics Sound cards are responsible for transforming bits stored in an audio file into music, sound effects, and narrations. Digital signal processor Transforms analog waves to digital bits when you make a sound recording Transforms digital bits into analog waves when you play a digital audio file Handles compression and decompression

17. Chapter 8: Digital Media 13 Digital Audio Basics The most popular digital audio formats include AAC, AIFF, MP3, RealAudio, Wave, and WMA Audio or media player software allows you to record and play digital audio files You can embed digital audio files into a Web page. Streaming audio plays as its file is downloaded, avoiding lengthy delays (entire file downloaded)

18. Chapter 8: Digital Media 14 Portable Audio Players Pocket-sized, battery-powered device that stores digital music. Digital music is available from a wide variety of sources Formats include MP3, AAC, and WMA A series of digital music tracks in a portable device is known as a playlist.

19. Synthesized Sound While digital audio is a recording of real analog sound signals converted into digital signals, synthesized sound is an artificially created, sound. Synthetic Artificial . Chapter 8: Digital Media 15

20. Chapter 8: Digital Media 16 MIDI Music MIDI (Musical Instrument Digital Interface) specifies a standard way to store music data for synthesizers, electronic MIDI instruments, and computers MIDI-capable sound cards contain aWavetable (set of prerecorded musical instrument sounds) Does not produce high-quality vocals Does not have full resonance of “real” sound Midi Files have a non-Wave form, they contain instructions as to how to create the sound, rather than a digitized version of the actual sound

21. Chapter 8: Digital Media 17 MIDI Music Wav file Midi file MIDI music tends not to have the full resonance of digital audio.

22. Chapter 8: Digital Media 18 MIDI Music Music composition software provides tools for entering notes, specifying instruments, printing sheet music, and saving compositions in formats such as MIDI.

23. Digital Audio Basics Samplers: Instruments that can digitize, or sample audio sounds, turn them into notes, and play them back at any pitch. Synthesizer: An electronic instrument that synthesize (manufacture, create) sounds using mathematical formulas. Sequencers: Interprets the sequence of MIDI commands Slide 19

24. Music Studio Before: Synthesizers Samplers Other Instruments Today… + Sequencers Virtual instruments Computer keyboards and Music keyboards Professional-level multi-track recording and editing studio that fits in a suitcase.

25. Electronica Electronic Music technology has transformed the world of a musician Electronica: Music designed from the ground up with digital technology Some of the most interesting sequenced music. Unleash the musician in the rest of us. No limits, can go from Classic to Rock Slide 21

26. Digital Audio Basics Sound Data is also called Waveform Audio Sound Editing is the manipulation of a visual image of the sound's waveform. Chapter 8: Digital Media 22

27. Change a sound's volume Change a sound's pitch Add special effects Echoes Remove irrelevant noises Rearrange musical passages Include voices (or mix) Include non-electronic instruments in the mix. Slide 23 Sound Editing Software

28. Chapter 8: Digital Media 24 Speech Recognition and Synthesis Speech synthesis is the process by which machines produce sound resembling spoken words Phoneme: a basic sound unit, like a syllable, that are stringed together to form words. Text-to-speech software: generate sound played through your computer’s standard sound card. Key technology in mobile comunications

29. Chapter 8: Digital Media 25 Speech Recognition and Synthesis Speech recognition or voice recognition refers to the ability of a machine to understand spoken words Speech recognition software is in charge of processing words spoken into a microphone that’s attached to the sound card (that is in charge of changing the analog data into digital data).

30. Chapter 8: Digital Media 26 Speech Recognition and Synthesis

31. Chapter 8: Digital Media 27