When it comes to producing, recording and mixing insanely fast metal music, timing is everything. It sounds like an oxymoron, but metal needs to be clean. Not in tone, but in production.
It needs precision, clarity and tightness in every instrument, so that the aggressiveness and tight rhythm punches through your speakers. If not, you'll hear an indecipherable mess of overly distorted guitars, drunkenly played bass lines, and drums that are completely washed out by the sound of the cymbals.
Let's dive into some easy to use advice on how to create a better metal music production.
1. Get the Timing Tight
Tight on Time
Metal music usually revolves around the powerful riffs of the electric guitars. For incredibly fast riffs you'll need some incredibly good players.
If you have two guitar players their riffs need to align almost exactly. If not, you'll end up with a riff that simply sounds sloppy. There will always be a pseudo chorus effect when you have two different players, especially if you make them double track their parts as well. However, if you don't make sure those guitar riffs line up exactly to the time, you'll lose the power of the mix immediately. Never mind the great vocal performance or the awesome drum sound you got. If the riff sounds sloppy, that's all anybody's going to hear.
Now, the easiest way to do this is to simply get amazing players that can play really tight. The alternative is the painstaking editing process of syncing up all the guitars with everything else. I do not recommend this unless you only have a few spots here and there that you need fixed. Usually, if the guitarist is that good, it'll take less time to move the 2-3 parts around than to re-record the whole performance. If he isn't, send him home until he is.
The same goes for the bass guitar. It has to be locked into the guitar riff as much as possible. Any variation can cause the riff to sound sloppy.
This sort of attention to detail is what differentiates a metal production from a folk or rock song. You can get by with the occasional loose playing when you're strumming an acoustic guitar, or playing some indie guitar riff. But the key to making a metal riff work is a locked in riff from all the instruments.
The Reverse Way of Making Your Low End Tighter
I forget which band did this, but I thought it was an interesting approach to recording both guitars and bass. After this metal band had recorded the drums, they started with the guitars before they recorded bass. They probably had a guide bass to record the drums to, but the reason behind it was that the bass would take up too much space if it were recorded beforehand.
Their philosophy was to create the tightest, thickest guitar sound possible, because their songs mostly revolved around the guitar riffs anyway. So by recording their guitars first they had the opportunity to thicken them up because they wouldn't clutter up the mix when combined with the bass. Then, later on when the guitars were done, the bass player and the producer found a sound that complimented the sound of the preexisting electric guitars that they already recorded.
It seems like a counterintuitive way of recording bass but this sort of fill-in-the-gap bass recording sounded good to them.
2. Get the EQ Tight
In the same vein as before, using a bass approach to EQing guitars can also help. Since guitars aren't as bass-heavy as the bass guitar, boosting the lows in the guitars can produce a smoother effect than boosting the bass guitar.
A boost in 100 Hz in the bass guitar might cause undesired boom or mud while boosting the guitars could create a thicker and tighter sound. That way you could actually reduce mud in the bass while increasing tightness and thickness in the overall riff production.
Don't Fear the Filter
On the higher end of things, low-pass filters are your best friends to get rid of the hiss you get from distortion. Slapping a high-cut filter down to 12 kHz or so can clean up the unnecessary noise you get from very distorted or overdriven guitar amps or cheap stomp boxes.
The same goes for high-pass filters. The lowest rumble of the bass guitar (around 40-50 Hz) can easily be cut out without compromising the thickness of the bass.
Additionally, an overabundance of high-mids in the 4 kHz area can also cause a fatiguing guitar tone. Smoothing out your guitar by subtly cutting that area will reduce the harshness of your guitar while still keeping the aggressiveness of the guitar tone. A rounder tone with the same attack.
3. Don't Sacrifice Tightness for Space
Lastly, you might be tempted to use reverb to create a sense of space. While you definitely should use reverb in your mixes, metal music requires particular attention to it.
A little bit too much reverb on the guitars and you'll go back to the sloppy mess of sound that you've worked so hard to stay away from. If anything, short delays to create additional thickness will work better because they not only add a sense of depth to your guitar production but they also add another layer of guitars to your riffs.
As I've said before, attention to detail is crucial and adding too much space to really fast guitar playing will inevitably muddy up your production.
Conclusion: Take the Careful Approach
Producing the rhythm section of metal music comes down to a certain mentality. You can't slack off and make do with things that aren't 100% perfect. A small, uneven section in the rhythm section creates immediate sloppiness for the whole mix, resulting in an amateurish production just because there wasn't enough attention to detail.
Make sure your players are great, make your guitars and bass fit together and don't add too much space and you'll end up with a stellar metal production.