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Sound in multimedia

Sound in multimedia. How many of you like the use of audio in The Universal Machine ? What about The Universal Computer ? Why or why not? Does your preference reflect a particular learning style? Will any of you be using audio in your projects? How?. Measuring sound.

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Sound in multimedia

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  1. Sound in multimedia • How many of you like the use of audio in The Universal Machine? • What about The Universal Computer? • Why or why not? Does your preference reflect a particular learning style? • Will any of you be using audio in your projects? How?

  2. Measuring sound • Sound is measured in decibels (db), the pressure or volume: • typical voice conversation is ~70db, • a soft whisper is 30db, • a jackhammer is 120db • Decibels measure the energy required to make sounds logarithmically • A jackhammer’s noise is about 1 watt, but voice conversation is 1/100,000 watt

  3. MIDI • A notation similar to a musical score • A communications standard describing how electronic instruments and synthesizers play musical sound • Advantages: • Often smaller than digital wave form files • Can be stretched or edited more easily • Exploits quality of good playback instruments • Disadvantages: • Playback not reliable, depends on instruments • Can’t play speech

  4. Digital audio • Windows uses WAV format, Apple uses AIFF • Advantages: • Reliable playback (“what you hear is what you get”) • Required for speech playback • Sound effects in \windows\media or the web • Are any of you planning to use simple digitized sound effects in your projects? • How so? Where are you getting your sound effects?

  5. Digitized sound is sampled ·Sampling frequency/rate: how often the sound sample is taken ·Sampling size: how much information is stored per sample

  6. Quantization • More sampling and more data improves quality and resolution • Value of each sample is rounded off to nearest integer (hence, quantization) • 8-bit sampling size provides 256 bits to describe dynamic range of amplitude • 16-bit sampling size provides over 65 thousand bits for dynamic range, but significantly increases space requirements

  7. Clipping • Occurs if amplitude exceeds intervals • Clipping produces hiss or other distortions

  8. Computing the size of a digital recording • Sampling rate * duration (seconds) * (bit resolution / 8) * 1 (mono) or 2 (stereo) • E.g., for a 10 second recording at 20.05 kHz, 8-bit resolution, monophonic (good for speech): • 22050 kilohertz * 10 seconds * 8/8 * 1 = 220,500 bytes • Or, for 10 seconds of good music quality at 44.1 kHz, 16-bit resolution, stereo: • 44100 kHz * 10 * 16/8 * 2 = 1,764,000 bytes • “Red Book” standard (ISO 10149) for CD-quality audio • Expensive for multimedia • Playing 16-bit resolution requires 16-bit sound cards

  9. Compression of digital audio • Compression algorithms can reduce file size by about an order of magnitude • Downside? More clipping, sound degradation • Authorware: Shockwave Audio (SWA) • Xtras->Other->Convert WAV to SWA • Also Voxware (better for speech) • Flash: on import, converts wav to 128kb mp3 • Stored automatically as symbols in library • Select imported sound from frame properties • Why might it be better to convert some wav files to mp3 outside of Flash?

  10. Compression of digital audio • Compression algorithms can reduce file size by about an order of magnitude • Downside? More clipping, sound degradation • Authorware: Shockwave Audio (SWA) • Xtras->Other->Convert WAV to SWA • Also Voxware (better for speech) • Flash: on import, converts wav to 128kb mp3 • Why might it be better to convert some wav files to mp3 outside of Flash?

  11. Importing sound into Flash Converts tada.wav to mp3 internally

  12. Flash stores sound as symbols Click on frame, go to Properties inspector, then select Sound from list

  13. Controlling sounds in Flash Sync options: Effect options: Event: synchronizes the sound to an event, such as a button click Start: same as event, except it won’t start new instance of new sound Stop: silences this sound (also see action StopAllSounds) Stream: keeps sound in sync with animation on a web site; sound won’t play longer than the number of frames it occupies

  14. Tips for recording sound • Use a decent quality microphone • Should eliminate noise when silent • Choose narrators who speak clearly • Coach your narrator for pronunciation, emphasis • A sound editor lets you manipulate sound • Trimming: removing white or empty space • Splicing: combining parts of several sounds • Amplifying: adjusting volume (for consistency) • Re-sampling (e.g., from 16-bit down to 8-bit) • Conversion and compression (e.g., wav to mp3)

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