Sight in Sound: Metering Frequencies with Spectral Analysis

Spectral analysers are a useful tool for helping to diagnose troublesome frequencies in your mix, weather it be low-end rumble, a pokey mid-range spike or a piercing high frequency. Of course a visual representation of your music is substitute for your ears and trusted monitoring systems but using it conjunction with these can iron out frequencies that are letting your mix down and might go undetected.

So what is spectral analysis? It’s simply a graph mapping frequency (or pitch) on the x-axis against amplitude (or volume) on the y-axis. A spectral analyser can be placed anywhere in the plugin-chain, but ordinarily at the end makes most sense. Placing it on your master channel is going to give you the most flexibility as you can solo a sound/group of sounds if you need to check those.

Many EQs will come bundled with a spectral analyser as standard, including Fab-Filter’s Pro-Q and Logic and Live’s default basic EQs, but for this I want to look at Voxengo SPAN, which is free and highly customiseable.

To get going with spectral analysis, it’s necessary to understand a little about frequency, and what you’d typically expect to hear where. To the left are lower sounds and to the right are higher sounds, so that’s sub-bass, kick drums, bass guitar and such to the left, all sorts of cymbals, noisy risers, distorted sounds to the right. In the middle is everything else.

Knowing where your sounds should sit in relationship to each other is key to getting a balanced sound. As you can see, lots of sounds have the potential to overlap and allowing each sound space to breathe is going to give you more clarity and headroom when mixing. Practically, this means you might need to be surgical with EQing and careful about which sounds overlap, the stereo image and reverb. All of these factors will determine how your overall sound is perceived. A sound in solo might sound great, but in context it could be muddy/distracting.

Kick Drums

Let’s take a listen to four distinct kick drums:

Kick 1

Kick 1 has a beefy low-end, with the fundamental (strongest, lowest tone) sitting around 50-60 Hz. Note there are  also peaks in and around 2-8k Hz, which is where the sounds prominent ‘punch’ comes from. This is a complete sounding kick, with the right low-end and snap ratio.

Kick 2

This kick has a similar fundamental but less sub content below it, and there’s also a more noticeable peak at 150 Hz. There’s presence around 2-8 kHz region too, but it’s far busier and cluttered. There’s also a sharp tail-off in the extreme high-end (18-19 kHz). This is a hollower, roomier kick than the first example, probably lifted from a recorded kit rather than a drum machine or sampler.

Kick 3

Similarly to kick 2, there’s an abrasive high-mid frequency grouping. The tail-off is less harsh than kick 2, and scooping in the mid-range (300-800 Hz) is less obvious too. This kick sounds layered to me, it has a low-end similar to a drum machine but the top end is likely from a breakbeat or similar.

Kick 4

Finally, kick 4 is the subbiest of the four, with the fundamental falling in pitch more audibly and with? less high-end content. The sound is almost non-existent past 6 kHz. This kick is probably from a TR-808 or emulation of it.

Snare Drums

I’m going to look at 4 snares from classic breakbeats. A snare’s fundamentals tend to sit around 150-200 Hz (created by the stick hitting the top skin); the rattle, or snare, is the higher-end content.

Snare 1

This snare is from The 5th Dimension – The Rainmaker. This was famously sampled (and pitched down a fair bit) in Notorious B.I.G.’s ‘You’re Nobody (Til Somebody Kills You)’. The snare itself sits around 200 Hz but there’s also some hi-hat bleed which is why there are prominent high frequencies.

Snare 2

This next snare is from Kashmere Stage Band – Scorpio. The ‘Scorpio break’ has been used countless times in Hip Hop and Drum’n’Bass, mostly lifted from Dennis Coffey and the Detroit Guitars Band’s original. It’s higher pitched than the last example (fundamental around 240 Hz) and there’s a spike at 574 Hz, too.

Snare 3

Next, this is from Roy Ayers Ubiquity – The Boogie Back, which you may have heard in N.W.A’s ‘Fuck Tha Police’. This snare feels fuller and phatter, despite the fundamental only being around 210 Hz. There’s more sub-content in this (which you may want to hi-pass filter out) but less noticeable bleed from other drum sounds.

Snare 4

Lastly, we have Billy Squier – The Big Beat, sampled in Dizzee Rascal’s ‘Fix up, look sharp‘. It’s a really full-sounding snare, struck hard and compressed quite a lot (which has brought up the room sound). Again, the fundamental is above 200 Hz, but notice the amount of bass/sub below it.

Balancing Act

The sonic relationship of sounds is key to getting the best out of your mix, so what can be done about it? Spectral analysis can point us in the direction of some troublesome frequencies. Using ‘Kick 1′ from our earlier example, and a few other loops from Sample Magic’s Vintage House pack, we can see where you might start EQing sounds.

Here’s the kick and top-loop together:

I looked at the top loop in solo mode, and noticed there were frequencies below snare sound that would clash with my kick and bass:

There’s unnecessary dub below 100 Hz, so I removed that with the Logic EQ (which has a built-in spectral analyser):

Next, I removed some of the 150 Hz frequency on the kick drum as this would clash with the snare if too dominant. It’s worth noting I am using a narrow Q and only taking a few dB off here. I also added a small pad around where the hi-hat would be sitting:

Finally adding the bass line in I balanced all the levels so they were sitting nicely, nothing sticking out of the mix, with the hi-hats and kick drum sitting at a similar volume:

The difference is not drastic, as we don’t want to drastically change sounds. But frequencies fighting for the same space will sound muddy and clumsy on decent monitoring or a club sound system. It’s worth checking out of a few different spectral analysers, the ones that come bundled with your DAW and other ones – they all might give you a slightly different read-out (nothing is perfect) and provide other useful data such as Peak and RMS levels, phase correlation tools, goniometer etc.