Life has many unanswered questions. Why do we exist? What is our purpose? What is the meaning of life? What was Mona Lisa thinking? And, of course, how do I get a tight low end in my mix? I probably hear this question more often than any other in the world of recording music. And, to be honest, it’s something that I myself often ponder and even struggle with, like a well-matched arm-wrestling opponent: I know I can win, but it doesn’t always prove easy.Tweaking the low end in a mix often revolves around listening on many different sources like car stereos, “boom boxes”, and yet smaller computer speakers. Different systems will attenuate or boost different frequency ranges, perhaps re-shaping your mix for the better but usually for the worse. Whatever happens, keep making comparisons until you find an average sound spectrum that works for everything.
While in the midst of this process remember that a mix’s low end isn’t just the bass guitar, or even the kick drum. It’s the sum of the whole. Acoustic guitars, electric guitars, vocals, and many other instruments can have a lot of low frequency content, all playing a role in the mix. Here, however, we’re going to specifically look at the bass guitar and how compression can be used to perfect a mix. Let me begin by pointing out that bass compression isn’t always needed. There are two typical reasons for compressing a bass (and most things in general): getting the notes to “sit” in the track and not poke out, i.e. limiting dynamic range, and/or because you like the sound of the compression.
The reasons for needing to limit dynamic range are obvious, especially with players who aren’t up to snuff. The bass needs to be even from note to note; otherwise some notes will be thunderous, earth-shattering affairs while others get lost in the mix. Listen to any pop music and you’ll notice how even the bass tends to be. Provide a solid foundation at the base and the tune will rock. With an uneven bottom level, however, the mix will teeter and never sit up straight.
The second reason for compressing bass may not be as obvious. Often, with an excellent player, the notes will be incredibly even to begin with and you won’t find it necessary to control the dynamic range very much if at all. This is an ideal situation, but you may still want to compress, even if only a small amount. The sound of the bass guitar, in rock music especially, has become largely defined by compression. 1–2 dB of gain reduction at a soft ratio may be plenty to get that sound, but still have some life and breath in the instrument. Now don’t squash that bass just yet... Check out these techniques for bass, and adapt them to your style and situation. We’ll cover the basics of compressor parameters in Part 1, and get into bass squashing trickery
in Part 2 next month. Here I’ll insert my standard disclaimer: these techniques may or may not work for you and are not hard and fast rules. Experiment. The good ol’ attack and release times... While preparing to write this article I asked my good friend Nick for any hot tips on the topic of bass compression (he always manages to glean neat ideas from the depths). He lightly chuckled and simply said, “Experiment a lot with the attack and release times.” Hmmm. Not the hot tip I was looking for, but it did illustrate the most important rule (actually, the Golden Rule) for compression of any signal: experiment a lot with the attack and release times. So, let’s review attack and release, as well as the general workings of the compressor. But first, the Threshold... Before attack and release, we need to decide when to compress: the threshold, the volume at which the compressor starts compressing. If the sound never gets higher than the threshold, you aren’t doing any compression. On the other hand, if it’s constantly higher than the threshold, the compressor will be squashing all of the time. Therefore, the lower the threshold, the more often you are compressing. ...and Ratio Now that we’ve decided on when to compress, we need to decide on how much to compress. This is expressed as a ratio—2:1, for example. In the case of 2:1, if the sound’s original volume goes 2 dB above threshold, it will only gain 1 dB on the output. As another example, at a ratio of 4:1, if the bass hits a note 8 dB louder than the threshold, a change of only 2 dB will be heard out of the compressor. Even fairly mild ratios can really cut down your dynamic range. Now we attack the attack and release! The attack time is the speed at which the compressor begins squashing once sound has crossed the threshold. It’s like reaction time. Once the sound crosses the threshold the compressor waits the length of the attack time before it compresses.
The attack time will greatly affect the initial sound of a note. In the case of the bass, a fast attack will soften the initial sharp plucking while a long attack will let the pluck through, causing the body of the note to be squished.
The release time is the speed at which the compressor lets go after the sound has traveled below the threshold. With a fast release the compressor will let go almost immediately after the sound goes below the threshold. A long release, however, will keep compressing for a while, even after the sound has gone below the threshold. And this is key to understanding release times. With an exceptionally long release the compressor will almost always be compressing, basically overruling the attack time setting. In the case of the bass (especially with sustained notes) it’s important to remember this relationship in order to preserve dynamic range (if that’s your goal). Now that we know how these parameters affect our bass sound, it’s time to get tricky. See you next time.
Justin Peacock is a producer/engineer/mixer based in Denver, Colorado, and is the Web Editor of Recording Magazine. You can check out his website at www.thehookfactory.com