Dynamic Range

Dynamic range describes the ratio of the softest sound to the loudest sound in a musical instrument or piece of electronic equipment. This ratio is measured in decibels (abbreviated as dB) units.

Dynamic measurements are used in audio equipment to indicate a component’s maximum output signal and to rate a system’s noise floor. As a reference point, the dynamic range of human hearing, the difference between the softest sound we can perceive and the loudest, is about 120 dB.

It is to describe the ratio of the amplitude of the loudest possible undistorted sine wave to the root mean square (rms) noise amplitude, say of a microphone or loudspeaker.The dynamic range of human hearing is roughly 140 dB, varying with frequency, from the threshold of hearing (around −9 dB SPL at 3 kHz) to thethreshold of pain (from 120–140 dB SPL. This wide dynamic range cannot be perceived all at once, however; the tensor tympani, stapedius muscle, and outer hair cellsall act as mechanical dynamic range compressors to adjust the sensitivity of the ear to different ambient levels.

The dynamic range of music as normally perceived in a concert hall doesn’t exceed 80 dB, and human speech is normally perceived over a range of about 40 dB.

It differs from the ratio of the maximum to minimum amplitude a given device can record, as a properly dithered recording device can record signals well below the noise RMS amplitude (noise floor).

For example, if the ceiling of a device is 5V (rms) and the noise floor is 10µV (rms) then the dynamic range is 500000:1, or 114 dB:

The decibel (dB) is a logarithmic unit. I will skip the maths here, but basically in terms of power, 120dB is about 1,000,000,000,000 times more powerful than 0dB.

Compressors, expanders, and noise gates are processing devices that are used in audio to alter the dynamic range of a given signal. This is done to achieve a more consistent sound when recording or as a special effect (by radically altering the dynamics of a sound, thereby creating a sound not possible from the original source).

• To make a recording sound louder by reducing its loudest sections, thus increasing the volume of the quiet sections (in mastering).

• To make individual elements in a recording stay at a more constant volume, for instance compressing a dynamic vocal so the quiet parts are not lost under the rest of the mix and the loud parts don’t leap out (in mixing).

The human ear is an amazingly delicate device, it can hear a huge range of volumes from the wind gently rustling in the trees to an exploding bomb.

With today’s recording and playback technology we have more dynamic range available than we can ever use. We have had 96dB of dynamic range available since the 80’s with CD. Earlier we demonstrated that the maximum range the average listener could hear was about 60dB, and would actually ever want was 30dB.

Very little recorded music today has 30dB of dynamic range. Many modern styles of music don’t require that much. Often dynamic range is reduced too much in mastering, this is the dark side of dynamic range compression and resulted in ‘the loudness war’