The Principles of Sound

Principles of Sound

Below is some theory for sound, useful to better understand audio production for engineers, mixing engineers and electronic music producers.

•   Sound is a means of communication
  
•   Communication involves 3 basic elements:
  
  1) Stimulus 2) Medium 3) Reception
  
• 
    Sound is produced in the form of a pressure wave caused by vibrations
  
  Frequency
  

•   The rate of vibrations determines the frequency of the sound
  
•   Frequency is defined as the number of cycles per second
  
•   Frequency is measured in Hertz (Hz)
  
•   Frequency is related to pitch
  
•   Frequency spectrum for the human ear is 20Hz to 20000Hz
  
•   The human ear does not perceive each frequency in the spectrum at an
  equal level of loudness
  
•   A common unit used to measure sound level is db SPL (Sound Pressure
  Level in decibels)
  
•   Phon is a measure of perceived loudness
  
•   High frequencies contain more directional information while low
  frequencies tend to be more omni-­‐directional
  
  Wavelength
  
   The physical dimension of 1 complete cycle  High frequencies have shorter wavelengths  Low frequencies have longer wavelengths  Longer wavelengths have more energy
  

Phase

•   The displacement in time of a wave
  
•   Phase shift occurs when waves of the same frequency are not similarly
  displaced
  
•   Can result in total cancellation of a particular frequency
  
•   Phase interference is commonly a result of direct and reflected sounds
  
  Harmonic Content
   Harmonics are integer multiples of the fundamental frequency  The fundamental frequency provides the basic tone of a sound
  
  Octaves
   An octave is the 8 note separation of a scale in modern music  It is a halving or doubling of frequency
  
  Waveforms
   Can be simple (a sine wave) or complex (speech)  White noise has equal energy per frequency
   Pink noise has equal energy per octave
  
  Acoustic Envelope
   An important aspect influencing the waveform of a sound is its envelope
   Every instrument produces its own envelope which works in combination
  with its timbre to determine the subjected sound of the instrument
   The envelope of a waveform describes the way its intensity varies from the
  time that the sound is produced until it dies away
   The envelope describes a relationship between time and amplitude  An acoustic envelope has 4 basic sections: Attack, Decay, Sustain and
  Release
  

Dynamic Range
 Dynamic range is the difference between the softest and loudest parts of a sound

Haas Effect
 2 similar sounds arriving within 30ms of each other will be perceived as 1 single sound. However, the earlier arriving sound will provide location information

Feedback Loop
 A feedback loop occurs between of an output signal and an input signal