Studio Log

Limiting and Mastering

Tuesday December 5th, 2006

It’s time for a little technical talk about limiting and mastering. I bring it up because I want to answer some questions that clients ask me all the time.

If you know anything about audio compressors then you can think of a limiter as an extreme form of a compressor. But for the unintiated and the curious, I will explain further without using a lot of numbers.

Any audio signal has a certain amount of variance in its volume; sometimes it’s going to be louder and sometimes it’s going to be softer. This is known as dynamic range and typically it‘s a good thing. If we spoke or played music at the same volume all of the time your ears would become fatigued and you would lose a lot of the subtle emotion and intensity of music or speech.

For the purposes of recording we often need to control dynamic range, so some crafty audio engineer invented the compressor. Compressors reduce the amount of variance in signal volume by reducing the louder parts of a signal by a predetermined ratio. Loud parts won’t sound quite so loud. Compressors then use a gain or “makeup” knob to compensate for the reduction in the loud parts. This means that the quiet parts are now louder and not so much quieter than the loud parts. The net effect is that the sound source is louder overall.

In music production I will often use a compressor on instruments like a bass or piano sound more defined and punchier because the compressors “compensation” effect tends to make the brighter (in these instruments quieter) components of the sound louder and more apparent.

Clients always ask about Mastering. What is Mastering? When do I need to Master? I hear that Mastering makes a huge difference in making my tunes sound louder and punchier, does it really??

Ok here’s the definition of Mastering from Wikipedia and it’s dead on:

Mastering is the process of preparing and transferring recorded audio to a medium that will be used in the production of copies. The specific medium varies, depending on the intended release format of the final product. For digital audio releases, there is more than one possible master medium, chosen based on replication factory requirements and/or record label security concerns. The chosen medium is then used as the source from which all copies will be made.

Ok, ya got it??? There wasn’t anything in there about making your mixes sound louder or punchier was there? Mastering is simply creating the master version that will be used to make copies of your album, cassette or CD. And it really should not be done until your mixes are final and the actual order of the songs for the master is determined.

So what about this louder, punchier thing? The fact is that this is a competitive business full of people who just can’t leave well enough alone and will try to improve an album’s sound right down to the very last moment.

Engineers used to use a bit of limiting when cutting masters for vinyl records to keep the grooves from being cut too wide by the cutting lathe. Eventually this techniqued was adapted, along with something called “normalization,” in order to get consistent level matching from one track to the next on a CD master.

Competition for air time on the radio and a desire to “stand out from the crowd,” has pushed mastering into being a big time business for some engineers. The popular thinking revolves around the idea that if your CD sounds louder than everyone else’s you will have a competitive edge with record companies and radio. So post mixing techniques that combined limiting and equalization and normalization have been tweaked and refined to the point where Mastering has changed from being a science into being an art. That’s really how it started and the rest is marketing.

Once professional engineers discovered what they could do to digital files after mixing, all of the semi-professional gear manufacturers came out with plug-ins or digital effects presets that simulated the sort of compression and eq adjustments that mastering engineers used. These then became “Mastering plug-ins.” Mastering plug-ins or presets usually combine some amount of limiting with a bit of eq in order to exaggerate a particular aspect of the music. Some examples include extensive low end gain for rap and hip hop tracks or increased mid range and upper mid range for vocal or guitar dominated rock records.

Often these plug-ins have a name involving a variation on the word “maximum.” So you’ll see things called Maxim, Sonic Maximizer, Maximizing limiters and so on. In some circles they’re referred to as brick wall limiters. Marketers like to put “Max” in the name rather than “brickwall limiter” because it sounds to the consumer as though their sound is getting bigger. But as I explained at the top of this article, sometimes you have to make things a little smaller before you can make them bigger.

Like every other process that an audio signal goes through Limiting can also make something sound worse if it’s done improperly or unnecessarily. With so much limiting being prevalent in a lot of popular music it just doesn’t seem very dynamic anymore. Why?? Badly mixed or mastered tunes will often lack any volume difference between “louder” and “softer” passages that can really draw a listener in and hook them on the emotional content of a song.

Recently there have been debates in professional audio publications and in the popular media arguing the merits of the trend to Limit/Maximize the living daylights out of every CD on radio. Bob Dylan said publicly that he didn’t think that music sounded like music anymore and indicated that it was as much to do with audio technology as with artistic quality.

Hopefully we are seeing the beginnings of a trend away from blindly making everything apparently louder. The human ear needs to hear quiet sounds, or even silence, not just loud material; or else everything sounds the same.

There are two good quotes to keep in mind on this topic. The great blues guitar legend B.B. King has often said that he doesn’t just play the notes, he also plays the spaces. The other quote is from the Pixar movie The Incredibles: “if everyone is super than no one is.”

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