Audio Frequency Fundamentals

Chart of the layout of an Orchestra from a frequency point of view and a diagram of the audio spectrum from a human point of sound.

Acoustic instruments with their fundamental frequencies

layout of an Orchestra's instruments with their fundamental frequencies

 

The traditional acoustic orchestra is divided into the following families

Plucked Strings
  • Harp
  • Guitar
  • Mandolin
  • Lute
 Bowed Strings
  • Violins
  • Violas
  • Chellos
  • Basses
 Woodwinds
  • Flute - Oboe
  • Clarinet
  • Bassoon
  • Saxophone
 Brass
  • Trumpet
  • Trombone
  • French Horns
  • Tuba
 Percussion
  • Timpani
  • Drums
  • Vibraphone
  • Bells
 

Human perception of the Audio/ Visual Spectrum - approximate values

Vision

  • Red 650 nm
  • Orange 630 nm
  • Yellow 575 nm
  • Green 400 nm
  • Blue 442 nm
  • Indigo 410 nm
  • Violet 400 nm


Speech /Song - Hz

  • 256Hz = Middle C
  • Soprano 250 Hz to 2 kHz
  • Contralto 195 Hz to 1 kHz
  • Tenor 100 Hz to 500 Hz
  • Baritone 80 Hz to 450 Hz
  • Bass 60Hz to 400 Hz

 Human perception
Human Audio Spectrum range is
approximately 20Hz to 20kHz


Hearing SPL

  • 140 dB - Threshold of pain
  • 130 dB - Jet plane take off
  • 110 dB - Pneumatic Drill
  •   80 dB - Average street corner
  •  30 dB to 20 dB Country side
  •    0 dB - Threshold of hearing

 

Hearing can be described using frequencies and volume.

Volume is measured  in units of dB, which is the loudness of a sound also called the Sound Pressure Level. SPL is measured in decibels which is one tenth of a bell. Frequencies are measured by units of Hertz or Hz

 

This table shows the musical intervals and the corresponding ratio of frequency to notes.

Note C
doh		   D
ray		   E
me		   F
fah		   G
soh		   A
lah		   B
te		   c
doh
Natural (Diatonic)
Scale frequency		 256   288   320   341   384   427   480   512
Intervals between notes   9/8   10/9   6/15   9/8   10/9   9/8   6/15  
Intervals between
notes above C		 1.000   1.125   1.250   1.333   1.500   1.667   1.825   2.000
Equal temperament
Scale Intervals above C		 1.000   1.122   1.1260   1.335   1.498   1.682   1.888   2.000
                               
                               

There are 12 semitones to the octave in the scale of equal temperament.

Middle C is equal to 256Hz or equal to 261.2 on the Helmholtz scale



Wavelength and Frequency

At 70 degrees Fahrenheit the speed of sound in air is approximately 1130 foot per second. This speed is temperature related and increases by 1 foot per second by a 1 degree raise of temperature, measured in Fahrenheit.

 sine wave

30hz   The wavelength of a sound wave is the distance between the beginning and the end of a cycle.

The higher the Frequency, [in Hertz], the longer the Wavelength [in Meters or Feet]
 
 


λ =   v
-
f
 v = velocity in the medium
f = the frequency in Hertz
λ = the wavelength

Further Reading