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


  •   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


     The physical dimension of 1 complete cycle
     High frequencies have shorter wavelengths
     Low frequencies have longer wavelengths
     Longer wavelengths have more energy


  •   The displacement in time of a wave

  •   Phase shift occurs when waves of the same frequency are not similarly


  •   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


     An octave is the 8 note separation of a scale in modern music
     It is a halving or doubling of frequency


     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


Dynamic Range

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

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

Feedback Loop

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