Sound in Multimedia Psychology of Sound

Give Examples:
! Psychology  of  sound   ! Sets  the  mood  
n    
n what  do  you  use  it  for?  
! Reinforces  a  message  
n what  techniques  for  its  communica7on  exist?   n    
! Science  of  sound   ! Creates  curiosity  and  interest  
n why  does  it  exist?   n    
n how  it  works?   ! Enhances  learning  
n    
! Technology  of  sound   ! Gives  feedback  
n how  do  we  capture  it?   n    
n how  do  we  edit  it?   ! Other  use  you  can  think  of:  
n how  do  we  use  it?   n    
! Wakes  up!  
 
! Check  out  “You  Don’t  Know  Jack!”  

Science of Sound Units

! Produced  by  vibra&on  of  object  in  air,  liquid   ! Frequency  (aka  pitch):    #cycles/7me  
  n Unit:  Hz  =  cycles/sec  
! Moves  through  waves  of  pressure   n Detec7ble  frequency  between  20  Hz  and  20KHz  
n Is  fast:  in  air,  340  m/sec  =  750  miles  per  hour    
n But  not  very  fast  (echo)  
  ! Amplitude  (aka  loudness):  height  of  wave  
! Characteris7cs  of  sound  wave   n Unit:  deciBell  

Amplitude Amplitude
Crest Cycle Crest Cycle

Time Time

Valley Valley

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Digitizing Sound From Analog to Digital

! Sampling  Rate  
Sampling Rate:
n Unit:  Hz  =  samples/sec  
Sample the sound amplitude often enough
So that you get a close measurement. n Usually  between  11.0,  22.0  or  44.1  KHz  
 
Bit-resolution: ! Bit-­‐resolu&on  (Recording  resolu7on)  
Use a detailed “ruler” n #  of  bits  devoted  to  record  each  sample  
So that you get a more accurate reading
n Usually  between  8,  16  or  24  bits  
 
! Space  Requirements  for  mono  
n sampling  rate  *  bit-­‐resolu7on/8  *  recording  7me  
The reproduced signal n 44.1  KHz  *  24/8  Bytes  =  132.3  KB/sec!  
might not be identical to the original n 1  hour  of  uncompressed  stereo  =    
But might be “good enough”

44.1 samples/sec * 3 B * 60 sec/min * 60 min/hour * 2 = 930MB

Space Requirements Digital beats Analog

good narration quite decent ! Analog  sound  is  stored  in    

and music if audio CD quality
n magne7c  tapes,    
tight on space
n LP  disks  
11000
10000 ! Digital  sound  
9000
8000
7000 n is  of  higher  quality  (hiss-­‐less)  
6000
5000
4000
3000 16 bit
n transfers  recording  without  loss  of  quality  
2000
1000
0 8 bit
n does  not  wear  with  mul7ple  playings  
loses depth
like AM 11KHz
22KHz
44KHz n can  access  recorded  data  randomly  (not  serially)  
radio - no stereo
n allows  easy  and  accurate  synchroniza7on  
advantage
! Digital  is  befer.  Period.  

These are for stereo. For mono, half the space is needed.

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Audio File Formats Technology of Sound: Amadeus II

! AIFF  —  “audio  interchange  file  format”   ! Recording  op7ons   ! Editing Options

n Consistency  in  audio  quality     Splicing and Assembling
n Microphone  (internal)   n
n The  old  standard  -­‐  Can  keep  track  of  audio  markers!   n Echo
n External  Audio  
n Amplify
! MP3  -­‐-­‐  highly  compressed  audio   n Internal  CD   n Filter
n The  new  standard  –  cannot  keep  track  of  audio  markers!     n Fade in / Fade out
 
! Sound  Format   (enveloping)
! Other  formats:   n Normalize
n If  you  use  audio  markers,  
n WAV  —  Microsol;  8-­‐bit  and  16-­‐bit   n Reverse
use  AIFF,  else  MP3  is  befer  
n AU  —  Sun;  16-­‐bit  compressed   n Downsampling
n etc, etc.
! MIDI  —  descrip7ve  for  musical  instruments   n Use Help > Manual to find out!
n compa7bility  with  available  hardware  
n low  standards  for  processor  speeds  
n very  low  file  size:  1  min  =  6K  

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