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Understanding Multimedia Production: Exploring Sound, Audio, and File Compression

This guide delves into the fundamentals of multimedia production, focusing on sound and audio. It covers essential concepts such as the nature of sound, MIDI (Musical Instrument Digital Interface), and recorded audio. The principles of digitization, sampling rates, and how to calculate sound file sizes are explained in detail. Additionally, techniques for compressing audio files, differentiating between uncompressed formats like WAV and compressed formats like MP3, are discussed. This comprehensive overview equips you with the core knowledge needed for effective multimedia production.

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Understanding Multimedia Production: Exploring Sound, Audio, and File Compression

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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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