Why do CDs recorded recently sound louder than older recordings?
Here's a basic explanation that usually works well with "non technical" people:
CD is a digital medium, which means it has a very specific maximum level. The loudest amount of sound you can put on a cd is called "0". Since 0 is the max, all other sound works backwards from that point and is expressed as a negative number (-10, -20, etc). All cds have this maximum-- think of it as a global speed limit.
So, if all CDs have the exact same maximum level, why do some cds (specifically "modern" recordings) sound so much "louder" than other recordings. If the CD format has a global "speed limit"- it seems logical that one disc shouldn't be able to sound louder than another.
Most people assume older recording sound softer because they do not exploit the full level of CD- they are simply recorded quieter- and never achieve a sound level that reaches the maximum level. That isn't usually the case.
What is the case involves the reduction of dynamics. Newer recordings have much reduced dynamic range which results in the illusion of "loudness". By removing the dynamic range of a given sound using tools like compression and limiting, more of that sound can be crammed closer to the maximum level-- which causes the listener to perceive it as "louder". To say it another way: without a wide difference between loud and soft-- everything is simply perceived as "loud".
Here's an analogy that often helps folks to picture it:
Say you were bouncing on a trampoline. Above your head, there is a ceiling made of brick. You begin bouncing, and you find yourself bumping your head slightly on the brick ceiling. However, you really want to bounce higher...
So you start bouncing higher, and as you get up to the ceiling, you tuck your head a little, to prevent it from hitting the ceiling. And you want to bounce even higher...
So you start bouncing even higher, and now you have to tuck your head and shoulders a little, to prevent them from hitting the ceiling. You bounce higher. Now you tuck your whole upper body to prevent from hitting the ceiling.
Now think about what has just happened. Have you really bounced "higher"? No, not really- because the brick ceiling was always the limit of how high you could go. However- by ducking parts of your body out of the way, you created the illusion that you jumped higher, because more of your body was at the max point at any given time.
So, modern recording use tons of compression and limiting to basically "tuck the head and shoulders of the music" so that they can cram more up to the very tip top-- and it seems "louder" as a result.
For a visual example, here is a visual representation of the Creedence Clearwater Revival song
Fortunate Son, recorded circa 1969:
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Notice that the peaks of the song reach the maximum level- but the average level of the material (the thick dense part in the graph) is pretty low- like -6 or so.
Here is a visual representation of the Watchmen song
Stereo, recorded circa 1996:
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Notice that the peaks of this song also reach the SAME maximum level- but the average level of the material under the peaks is pretty giant-- the distance that the peaks are above the body of the sound has been reduced!
The dynamics of the song have been squashed- creating a "loud" mix that sounds "better" in your car or on the radio. You can see the material has just be smashed into a big block of sound.
The problem is that this reduction in dynamics is not a win-win situation. This reduction will often result in ear fatigue on the part of the listener- and will often have negative effects on the perceived quality of the music. By removing dynamics- one of the main elements of music expression is removed- and often results in a more sterile sounding finished product.
by Vince Maskeeper