I got an email from my father today directing me to an internet forum debate regarding how over-compression in mastering is ruining music today and I responded with what you’re about to read–the simplest, most easy-to-read breakdown on this topic I could come up with–an explanation that anyone will be able to understand. No flowery or abstract adjectives, just the meat and potatoes. If something still isn’t clear, leave a comment. I’m mostly posting this article to save myself some time (to direct our clients to) but this post may be helpful for other mastering engineers who’d like to do the same.

Note: this post refers to sound compression, not MP3 or zip compression. Learn more about the differences between sound compression and data compression here.

What Is Mastering Compression?

Mastering compression* (“limiting”) reduces the dynamic range of a recording. Dynamic range is the range between the loudest and quietest point in a recording or section of a recording. Dynamics and loudness are inversely proportional: the less dynamic a recording is, the higher the average loudness of that recording can be, and vice versa. Today, there is said to be a ‘Loudness War’ between labels trying to release the loudest records possible.

The Pros and Cons of Loudness

When we’re talking about the consequences of loudness, we’re really talking about two different things:

• From a macro perspective: A louder/less dynamic recording means all of the sections of the song will be about the same volume. For ‘Verse Chorus Verse’ style songs, the benefit is that the song comes in loud right off the bat and stays loud from section to section. The downside is it means the chorus doesn’t “hit you” or sound as big as it otherwise might because there is little or no change from the verse to the chorus. In fact, if there’s more stuff going on during the chorus, individual elements may actually get smaller. For example, heavily compressed rock mixes tend to have a bigger snare sound during the verses than the choruses.
• From a micro perspective: Compression from one beat to another is hard for the untrained ear to hear, unless it’s very extreme. And even then it is hard to explain what it is you’re hearing–you just know it sounds bad. At this scale, compression makes the mix sound more “exciting” right away, but if overdone can be fatiguing on the ear to listen to. Perhaps more importantly, the drums will often be less punchy if a mix is more heavily compressed.** A former coworker and assistant to one of my all-time favorite mixers once said to me, “mastering ruins everything.”

Is Louder Better?

There was a psychological study which showed that people consistently prefer recordings that are louder, even by an increment as small as 1 dB, even when they’re not told what the change is. (Anyone want to find the link for me?) If you want an extreme example of over-compression, just listen to the radio. They use a more complex system of compression to get recordings even louder than CDs. And yet for every person who puts up a fuss in the blogosphere/messageboardiverse about mastering ruining music today, I have a memory of someone in my childhood telling me how they like the sound of radio. It just has that magic je ne sais quoi. There have been studies which indicate that loudness has a strong effect on which radio station a person will stop on when channel surfing.

While I consider myself to be more of a ‘new school’ engineer rather than one pining for the days of yore, I sometimes wish more records today had bigger dynamic changes. My favorite example is “Quiet” by the Smashing Pumpkins, which came out in 1993 before the Loudness Wars really began. It will probably be hard to tell on YouTube, but when the guitar solo comes in on the record, the song just gets so much louder. If you already have the song cranked, the solo will hurt your ears a little bit. Now that, ladies and gentlemen, is rock & roll.

For a case study in consumer backlash against loudness, check out my post about the Metallica album Death Magnetic.

*The type of compression I’m talking about here is “limiting”, a specific type of compression that comes at the end of every mastering engineer’s signal chain. I’m using the term compression throughout the post because it will be more familiar to musicians and readers.

**If I know that a project I’m mixing will be mastered by someone else, I usually try to make my drums a little punchier than I want them in order to compensate for the effect that mastering will have, unless I know the mastering engineer tends to go easy on the compression. This is also why it is usually best to select a mastering engineer that your mix engineer has worked with in the past, so that the mix engineer can anticipate what will happen to the mix in the mastering stage and mix accordingly.

When Nirvana’s Nevermind came out, it was touted as one of the loudest albums ever released. Today, if that album came onto your iTunes playlist after Death Magnetic, you’d have to turn your speakers up considerably to hear it.*

Psychological studies have shown that a recording’s loudness dramatically affects how much people like a song and how likely it is that a person will stop on a certain radio station. The solution? Limiting: a process which effectively turns up the quietest parts of a recording, automatically raising its overall loudness. A limiter is one of the last pieces in the mastering signal chain and arguably the most important.

Done properly, limiting can add energy to a song. Taking it too far a la Death Magnetic, however, may cause ear fatigue, a subconscious phenomenon akin to reading under dim light, straining the listener’s ears and making him or her want to turn off the music after extended listening periods.

Metallica‘s latest has received a flood of criticism and media attention regarding the presence of over-limiting and digital clipping, an unpleasant-sounding distortion that occurs when a sound medium is overloaded beyond its volume limit.

The audio community has been debating the so-called “loudness war” for years but never before have consumers been able to hear the difference for themselves. Enter Guitar Hero: World Tour, which allows users to access an unmastered version of Death Magnetic – and it sounds a lot better.

Mastering engineer Ted Jensen defends himself:

“In this case the mixes were already [over-limited] before they arrived at my place […] I would never be pushed to overdrive things as far as they are here. Believe me I’m not proud to be associated with this one, and we can only hope that some good will come from this in some form of backlash against volume [being seen as the most important thing].”

It is hard to say who is responsible. The engineers who worked on the album have otherwise stellar track records. In any case, Death Magnetic may represent a new kind of revolution: one that gets quieter.

Personally, I find that clipping can benefit some recordings, but this new Metallica record took it too far. Add to this the fake-sounding drums and we’re left with one of the worst sound major recordings in recent years. What do you think? And to those of you who aren’t audio engineers: did you notice?

Also note: Another result of the loudness war is that many record labels have released “digitally remastered” versions of classic albums in order to compete with today’s recordings. If you want to compare Nevermind to Death Magnetic, use the original release for full effect.

*Soundcheck notwithstanding.

Sources: Tape Op (Nov/Dec ’08), AllMusic.com