Dynamic Range is another one of those audio buzz-terms that gets thrown around a lot, but what exactly is dynamic range? In short, it is the range between silence and the very loudest sound.
Dynamic Range (DNR) comes into play when talking about human perception of sight or sound. Humans can hear sounds across an incredible range of volume – in short, our dynamic range is quite large. The problem is we can’t hear loud noises at the same time we hear soft noises. Our ears take some time to adjust to the differences in volume that may occur during a musical passage. With live (especially non-amplified) music this is what makes the experience so exciting. With recorded music, one of the largest tasks of an engineer designing a link in the audio chain is that the equipment (amp, speakers, et al) responds to the changes in dynamics accurately so the listening experience is as natural as possible.
Dynamic range gives music its emotional excitement. From a stirring orchestral piece to the intro of a raging guitar solo it’s not the notes that carry us away, it’s the dynamic range of the notes. A singer’s plaintive whisper draws us into her sadness until she carries us away with emotion at the top of her volume range in the next measure.
Differing versions of the same song or album may have been released at different times for different reasons so the DNR of the same song from two different releases may vary greatly. In short, the greater the dynamic range the greater the difference between quiet and loud. This does not necessarily mean a recording of a dance track with a DNR of 4dB is a worse recording than a symphonic recording of a classical piece at 14dB, it just means the music is different. However, if you have two versions of the same song and version A has a DNR of 4dB while version B has a DNR of 5dB, version B will be the better sounding version.
This is an important fact when the conversation turns to dynamic compression and how the overuse of compressors in audio production sometimes makes music difficult and fatiguing to listen to. Our ears need a rest – if even for an instant – between volume changes. When the music is compressed those changes don’t occur naturally (if at all) so our ears never get the chance to rest and adjust causing fatigue. Fatigued ears don’t enjoy music as much and therefore don’t listen as much as ears that get the chance to adjust naturally.
The dynamic range of the human ear is typically 140dB which is roughly equivalent to the sound of a bee buzzing in an otherwise silent meadow on a summer day to the roar of a 737 at takeoff. We can hear those differences, but our ears need time to adjust to them, if even for only an instant.
A cassette tape is capable of performance ranges of 50 to 56dB while 16-bit audio is capable of 96dB. A vinyl record, played for the first time, can achieve up to 70dB but generally across the diameter of the record the DNR is less than 65dB. Twenty-four-bit digital audio formats are capable of up to 144dB DNR.
There are two ways to calculate and spec DNR: The Crest Factor and the R128 Standard:
Crest Factor – the difference between the average volume and the peak volume. Since it is an average measurement, long passages of very quiet music or long passages of very loud music can sway this number a great deal.
R128 Standard – computes the loudness at different places in a track while ignoring the silent passages. The resultant number is the difference between the 10th percentile to the 95th percentile of the volume which is simply a way of saying 95% of the volume sits below the top number and 10% sits above the lowest number. R128 is most commonly used outside of the recording studio.
When listening on a small Bluetooth speaker or car stereo while you’re busy doing other things, the DNR really doesn’t matter much, but when you want to listen to music for all of the emotional highs and lows it can provide you, dynamic range becomes important.