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Managing Digital Sound

Managing Digital Sound. Lecture Notes for Chapter 13 in the text Exploring the Digital Domain : An Introduction to Computing with Multimedia and Networking. Digital Sampling of Sound.

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Managing Digital Sound

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  1. Managing Digital Sound Lecture Notes for Chapter 13 in the text Exploring the Digital Domain: An Introduction to Computing with Multimedia and Networking

  2. Digital Sampling of Sound • Digital sound is sound that has been converted to, or created in, a discrete form (namely a set of numeric values) • Natural sound is a continuous phenomena and is converted to digital form by sampling techniques • Properties of sound waves • amplitude (measure of loudness) • frequency (measure of pitch)

  3. Continuous Sound Wave

  4. Sampling Sound • Spatial sampling • sample rate • resolution • Analog-to-digital converters (ADCs) • Digital-to-analog converters (DACs)

  5. Sampling of a Sound Wave Illustrated

  6. Sampling of a Sound Wave Illustrated (cont’d)

  7. Sampling of a Sound Wave Illustrated (cont’d)

  8. Resolution and Dynamic Range • Resolution depends on how much memory is devoted to storing individual sample amplitudes • 8-bit sound • 16-bit sound • Dynamic range and clipping

  9. Resolution Illustrated

  10. Storing Digital Sound • Sample rate and resolution -- tradeoffs • Voice and speech: 8-bit resolution and 5-10 KHz sample rate • CD-quality music: 16-bit or higher resolution and 44 KHz • Audio file compression • Sound on the Web • downloading and playing sound files • streaming audio

  11. Synthesizing Music • Simple waveforms and oscillators • Subtractive synthesis • Additive synthesis • FM synthesis • Phase distortion synthesis • ADSR (attack, decay, sustain, release) envelope • Integrated synthesis

  12. Oscillators

  13. ADSR Envelope

  14. MIDI Instruments and Devices • MIDI is a standard interface between electronic musical instruments and synthesizers • Devices which are MIDI-compatible can communicate with each other • Advantages to MIDI • files are encoded and are much smaller than digitized sound files • files can be easily edited and mixed for multiple tracks

  15. Speech Synthesis • Speech synthesis involves creating speech from written text • Analysis of written text focuses on breaking the text into phonemes • English employs approximately 50 basic phonemes • Rules allow a speech synthesis program to evaluate alternate pronunciations appropriate for the context • Such rule-based phoneme analysis produces excellent speech synthesis results

  16. Speech Recognition • Speech recognition attempts to interpret digitized speech for meaning • The task is complicated by the differences among speakers and even the different ways a given speaker might pronounce the same word depending on mood, context, etc. • Some success has been achieved by tailoring/training a program to recognize a particular speaker • Some reasonably successful voice activation systems have been produced where vocabulary is limited to samll number of words • Speech recognition remains a very challenging problem

  17. Speech RecognitionIllustrating the Difficulties

  18. Editing Digitized Sound • Digital sound editing is part of a larger field called digital signal processing • Once sound is digitized, it is in discrete numerical format • Numerical transformations on this data can be used to: • change the sound’s pitch • change the sound’s amplitude • add echoes and other special effects

  19. Summary • Digital sound is produced by sampling sound waves over time • A digital sound file consists of sampled amplitudes at a number of discrete times within a given time interval • The number of samples per second is called the sample rate • The number of bits devoted to storing individual sampled amplitudes is called the resolution of the digitized sound: 8-bit, 16-bit and higher resolutions are used depending on the kind of sound being digitized • Fidelity will be largely determined by the sample rate and resolution

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