Monday, June 24, 2013

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 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 


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