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Last week we started examining component parts of the audible spectrum.  Of those component parts, perhaps none is more misunderstood and mishandled than the sub.  Perhaps it’s all those cars with bumpin’ sound systems out there, but it seems like everyone wants to cram as much “sub” as they can in the mix.  Just make sure you know what you are asking for!

 

Firstly, I just have to provide a disclaimer that I think any car with a big subwoofer in the back sounds terrible to me.  Outside my studio someone was parked blaring some Lady Gaga tune or something like that and all I could hear was the sub.  I could hear it distinctly too despite being three walls and a hundred yards away.  I can’t help but think about how badly those people are destroying their ears.  Morever, it just plain doesn’t sound good to me.

 

As I mentioned last week:  for practical purposes, Sub-Bass should be anything that sounds below the lowest fundamental note of your song.  This can include percussion and any sub-harmonics, resonations, formants, and room tones.  These are frequencies that would really only be reproduced by sub-woofers and large format PA/sound reinforcement systems so even if you have a million dollar audio setup and can hear all the way down to 20 Hz, realize that 90% of your fans still won’t hear that.  As I mentioned in the Limitations article, most of this won’t be reproduced by any consumer grade sound system.

 

Moreover, the sub is for audio content that lacks position specificity.  If you’ve ever seen a surround sound set-up before, you know that there are 5 speakers (LCR and two rears) plus a single sub-woofer.  Sub frequencies are very difficult to locate spatially and will more or less sound like they are coming from the same place no matter the position of the loudspeaker.  This is why surround sound setups don’t also require 5 separate subs.  A single sub placed in the center will suffice for all positions in the surround soundstage.  Because of this, too much sub content will turn into a big muddy bass because there is no real way to separate the rumble of the kick from the rumble of the bass or the rumble of the synth.

 

In order to get a focused sounding sub—the kind that moves you in the club or the kind that is noticeable (in a pleasant way) in home hi-fi systems that can actually reproduce those frequencies—you need to alter your thinking about the sub.  Don’t think of it as a separate frequency band that needs to stand on its own merit or be equal to the other frequency bands.  In fact, it helps even more to think of it as a garnish on the bass.  Something to help emphasize the bass, but not overpower it or stand on its own. 

 

If your bass lives in the bass and mid range frequencies, adding in the sub should make it stand out all the more.  But the bass should not expressly be confined in the sub regions. 

 

Furthermore, a sub bass is more clearly defined by what is NOT in it and for how long.  Imagine a band consisting of a drummer, a bass player, a synth player, and maybe a string orchestra—rocking out 80s arena style.  With all of those instruments you have the OPTION of including all that information in the sub:  the kick drum, the bass formants, the synth sub-harmonics, and the orchestra formants.  There would also be additional room tones and environmental sounds all going into the sub.  Since the sub has no position specificity and because sounds are distinguished from each other predominantly by upper harmonics, the sub sounds will be big and washed out because you won’t easily be able to tell the sub-bass components of each instrument apart from each other.

 

This introduces the problem of muddled bass.  So a kick drum that is short in duration might get buried by the longer notes of the orchestra and synthesizer, so you might get more sub overall, but lose the clarity of the kick.  In these sub ranges, sounds are really just a rumble and boom so the only way to tell things apart is by relative volumes and note duration.  Cramming all that stuff together like in the example above obscures all that.  That just creates an audible but unusable low-frequency noise floor.

 

Instead, a more preferable choice is to be selective in what makes it to the sub woofer.  That’s how you really draw emphasis and get the most out of the sub frequencies.  Make the drummer sound like John Bonham by putting a high pass filter over the mix at 45 Hz and bypass the filter on the kick drum track or maybe the entire drumset.  Then the kick drum really gets beefy and the rest of the ensemble doesn’t cloud that portion of the spectrum.

 

If you have a ticky kick drum like Metallica, you could instead opt to make the bass guitar or orchestra super fat by sending that to the sub instead.  The point is to be selective about what information makes it to the woofer so as not to obfuscate the sonic image with unnecessary clutter.

 

Additionally, as I’ve mentioned before, it is imperative to understand that low frequencies are extremely power dense.  So if you are actually “hearing” anything below 40 Hz, you are taking up way too much of the power spectrum.  This will blow out speakers, distort channel strips, and otherwise yield bad mixes.  And in a closed system, this extreme bass content (which is barely audible) will steal precious headroom from the more important frequencies.

 

The important take home lessons are to not expect any of your listeners to hear any of the sub-bass.  For the majority of them, the sub doesn’t exist altogether.  For the rest of them, be selective in the sub-bass content in order to make sure that you are actually using the woofers properly.

More from Phil’s Audible Spectrum series:


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