Element of sound

• band: 20-20k Hz. 0~20Hz – infrasonic, > 20k Hz – Ultrasonic (supersonic)
• sound pressure level (SPL): variation above and below normal atmospheric pressure
• sound depends on the production of changes in atmospheric pressure
• acoustic masking: one sound can mask another sound, making it inaudible.
• If specify too high sample rate when replaying sound, the audio will sound squeaky. If the sample rate is too low, it will sound slow.
• Famous Note: (ref from class note)
  Middle C = 261.626 Hz (standard tuning)
  Concert A (A above middle C) = 440 Hz
  Middle C = 256 Hz (Scientific tuning)
  Lowest note on piano A=27.5 Hz
  Highest note on piano C= 4186.009
• Golden ears: can hear above 20kHz, dogs can hear 44kHz, cats up to 80kHz.
• The maximum frequency that can be heard gets lower with age and hearing damage.
• We hear best in the range of 200Hz to 4000Hz, close to the range of human's voice.
• Video has two spatial dimensions: width and height. Audio has one: loudness. Audio is stored as a series of measurements of loudness. In analog world, when sound is transmitted via speaker cables, those changes are changes in the voltage on the wire. [the last 3 items were added at 12/28/2009]
  

Storage - Stereo audio, 16 bits, 44k Hz sampling rate, PCM encoding in 3 minutes:
3 minutes x 60 sec/min x 44000 samples/sec x 16 bits/sample x 2 channel / (8 bits/byte) = 32MB