John,

The decibel scale is a relative scale. It's a comparison of how loud a sound is perceived to be when referenced against what's called the average threshhold of human hearing (that is, the softest sound the average person can hear).

When the decibel value is calculated this threshhold is -120 dB.

  • If you are interested, the calculation is...

    dB = 10Log(10^(-12)) where 10^(-12) is the sound intensity.

Using this threshhold reference, the range of the majority of sounds in our environment go from -120 to 0 dB. This is where the -ve scale is derived from. Below the threshhold of hearing (less than -120 dB) is often called -inf (for 'infinity') on a mixer. This is because below -120 dB is outside our hearing ability.

Because the dB scale is about comparisons, ultimately it's only the RANGE of the values that matter. From the above, since the values are from -120 dB to 0 dB, this gives a range of 120 dB from the very softest sound to the loudest sound.

If the negative scale is bothersome, then this RANGE of 120 dB can be represented by many alternatives; it all depends on what value a person assigns to the threshhold of hearing...

  • 0 dB (hearing threshhold) to 120 dB (loudest): the range is still 120 dB
  • -60 dB to +60 dB (range 120 dB)
  • -10 dB to +110 dB (range 120 db), etc.

Another important aspect of the dB scale is that if the dB value is doubled, this does not correspond to a doubling in volume. This is why it doesn't matter what the starting place of the scale is. All that matters is that from the low end to the high end is a range of 120 dB.

Regards,
Noel

MY SONGS...
Audiophile BIAB 2025