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Part A Multimedia Production

Part A Multimedia Production. Rico Yu. Part A Multimedia Production. Ch.1 Text Ch.2 Graphics Ch.3 Sound Ch.4 Animations Ch.5 Video. Multimedia. Text Graphics Audio information Animation

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Part A Multimedia Production

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  1. Part A Multimedia Production Rico Yu

  2. Part A Multimedia Production • Ch.1 Text • Ch.2 Graphics • Ch.3 Sound • Ch.4 Animations • Ch.5 Video

  3. Multimedia • Text • Graphics • Audio information • Animation • Videos

  4. Audio Information (Sound) • Nature of sound • MIDI • Recorded Audio

  5. 1. Nature of Sound • Wave pattern • Loudness, pitch

  6. Loudness (聲量) vs pitch (音高) • Curve  , sound louder • Curve narrower, pitch 

  7. Frequency (頻率) • e.g. 1kHz = 1000 Hz = 1000 peaks per second Frequency = # of peaks occur / second

  8. Frequency

  9. 2. MIDI • Musical Instrument Digital Interface • Stores musical notes played by piano, violin, etc. • Sound card synthesizes (合成) these notes • MIDI stores codes only • File size ~ several kB

  10. 3. Recorded Audio • Digital Audio • Sound recorded  digitised, stored in PC • All kinds of sound recorded from mic.  digital audio by sound card • Digitisation Analogue waves pattern Discrete values (Digital value)

  11. 3. Recorded Audio • Digitisation Digitisation Sampling Sampling Rate Sampling Size

  12. Sampling Rate • # of times measured height of sound per sec. • measured in Hz Sampling Rate > 2 x Max. Sound Freq.

  13. Sampling Rate Higher the sampling rate, better the quality, BUT larger the file size.

  14. Sampling Rate • Sampling Rate of Audio CD is 44.1 kHz • Max. Audible freq. is 20 kHz • Sampling Rate of Human speech is 11.1 kHz • Max. freq. of human is 4 kHz

  15. Sampling Size • # of bits used to stored • If sampling size small • very soft and loud sound can’t recorded • quality of recorded sound depends on it

  16. Sampling Size

  17. Mono and Stereo • Mono • Single Channel • Stereo • 2 Channels • Twice the file size of mono

  18. Calculating Sound file size File size = Channel # x Sampling rate x Sampling size x Duration / 8 bytes

  19. Calculating Sound file size • e.g. Given that a sampling rate of 44.1kHz and a sampling size of 16 bits is used to record a sound for onehour. What is the uncompressed file size if (a) the sound is mono, (b) the sound is stereo?

  20. Calculating Sound file size • Solution • For mono sound, the # of channel is one. Thus, File size= 1 x 44.1 x 103x 16 x (1 x 60 x 60) bits = 2.54 x 109 bits = 2.54 x 109 / 8 bytes = 3.17 x 108 bytes ~ 300 MB • For stereo sound, the file size is twice, i.e. ~600MB

  21. Calculating Sound file size • Ex. Given that a sampling rate of 44.1 kHz and a sampling size of 24 bits is used to record a sound for half an hour. What is the uncompressed file size if (a) the sound is mono, (b) the sound is stereo?

  22. Calculating Sound file size • Solution • For mono sound, the # of channel is one. Thus, File size = 1 x 44.1 x 103 x 24 x (30 x 60) bits = 1.91 x 109 bits = 1.91 x 109 / 8 bytes = 2.38 x 108 bytes ~ 238 MB • For stereo sound, the file size is twice, i.e. ~476MB

  23. Compressing Sound file • Raw sound is WAV, uncompressed. • WAV  MP3, compressed. • MP3 • Lossy compression • Can compress CD audio by 12

  24. Bit Rate • The speed of data transmission Bit Rate = Channel # x Sampling Rate x Sampling Size

  25. Bit Rate • e.g. The amount of bits for a 16-bit stereo music at 44.1kHz transferred in each second is 2 x 16 x 44.1k = 1411.2kbps bps = bits per second

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