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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 - PowerPoint PPT Presentation
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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 Videos
Audio Information (Sound)
Nature of sound MIDI Recorded Audio
1. Nature of Sound
Wave pattern Loudness, pitch
Loudness (聲量 ) vs pitch (音高 )
Curve , sound louder Curve narrower, pitch
Frequency (頻率 )
e.g. 1kHz = 1000 Hz
= 1000 peaks per second
Frequency = # of peaks occur / second
Frequency
Frequency
Audible sound 20 Hz ~ 20 kHz
Human speech < 4 kHz
Bat 20 ~ 120 kHz
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
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 patternDiscrete values(Digital value)
3. Recorded Audio
Digitisation
Digitisation
Sampling
Sampling Rate Sampling Size
Sampling Rate
# of times measured height of sound per sec. measured in Hz
Sampling Rate > 2 x Max. Sound Freq.
Sampling Rate
Higher the sampling rate, better the quality, BUT larger the file size.
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
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
Sampling Size
Sampling Rate Sampling Size
Spoken voice 11.1 kHz 8 – bit
CD-Audio 44.1 kHz 16 – bit
Professional recording
44.1 kHz 24 – bit
Mono and Stereo
Mono– Single Channel
Stereo– 2 Channels– Twice the file size of mono
Calculating Sound file size
File size = Channel # x Sampling rate x Sampling size
x Duration / 8 bytes
Calculating Sound file size
e.g.
Given that a sampling rate of 44.1 kHz and a sampling size of 16 bits is used to record a sound for one hour. What is the uncompressed file size if (a) the sound is mono,
(b) the sound is stereo?
Calculating Sound file size
Solution(a) For mono sound, the # of channel is one. Thus,
File size= 1 x 44.1 x 103 x 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
(b) For stereo sound, the file size is twice, i.e. ~600MB
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?
Calculating Sound file size
Solution(a) 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
(b) For stereo sound, the file size is twice, i.e. ~476MB
Compressing Sound file
Raw sound is WAV, uncompressed. WAV MP3, compressed. MP3
– Lossy compression– Can compress CD audio by 12
Bit Rate
The speed of data transmission
Bit Rate = Channel # x Sampling Rate x Sampling Size
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