The Great Unmasking: Solving Frequency Masking in the Mix

I made a big mistake! 
  

If there’s one mixing tip that should have featured in my book, 56 Mix Tips for the Small Recording Studio, it should have been about frequency masking. Sure, I mentioned it almost a dozen times in other tips, but frequency masking deserves its own discussion. So why is frequency masking such a big deal? Because if mixing engineers don’t have the skills and knowledge to resolve frequency masking in their mixes, they’re missing an essential step in the mixing process of a song. Fixing frequency masking problems enables you to add definition and clarity with relatively simple techniques and using plugins you can get for free. 
So here it is. Tip # 57.

Frequency masking occurs when two or more similar-sounding sources combine at similar volumes resulting in a reduction in clarity of the affected elements

In my experience, there are two reasons for making equalisation adjustments to any musical element in a music mix. It’s either for character or correction. This blog focuses on the correction aspect, and the why and how of using tone shaping to reduce frequency masking.

As a quick recap, frequency masking occurs when two or more similar-sounding sources combine at similar volumes resulting in a reduction in clarity of the affected elements. The masking occurs both at the fundamental frequency and its harmonics. In a typical song mix, the bulk of these similar-sounding elements occur in the mid-range, and this is where you should be spending most of your time tweaking and sculpting.

Imagine listening to a single male adult talking. Let’s assume his voice has a deep timbre. You can hear and comprehend him clearly because there is no other competing conversation. Add another two deep-voiced males talking at the same volume, and due to their tonal similarity, it’s difficult to hear any one of them. A simple fix would be to use panning to spread them apart, but while this is helpful, it’s not always effective since the underlying problem hasn’t been addressed: similar-sounding elements coinciding at the same level. Another partial fix is to raise the level of one of the three voices (or lower the level of the other two). While this improves the clarity of one of the voices, it further degrades the clarity of the remaining two.

If you are going to address only one of the three issues that cause masking (similarity, level, and timing) the simplest and most effective fix is to ensure that the competing elements don’t occur at the same time. However, this is only a practical option if you’re involved in the production and arrangement before recording, or you have an artist who’s happy for you to screw around with their recorded performance. So, that pretty much leaves us with equalisation and level adjustments as the remaining options. And these are very effective options during the mixing process.

But let’s back up a bit. Why? Because sorting your frequency masking issues before you get to the recording stage is the best and most effective method to clarity into your mixes. In other words, pre-production. Then, when you get to the mixing stage, you can use EQ and level adjustments to fine-tune your production.

In short, the goal is a holistic one: ensuring that there is variation in tonal character across all of the elements in the entire mix

   

For years, successful producers and recording engineers have used techniques like this to get great clarity into their song productions. They select instrumental elements with different tonal characters so that they have a clear distinction in the mix. When layering guitars, they use a variety of guitars, amps, and pickup selections. Chords would be played in different inversions to spread the chord voicings more evenly across the frequency spectrum. Backing vocalists would be chosen based on their tonal contrast amongst themselves and with the lead vocalist. And the same techniques would be used when combining keyboards, horns, and with guitars. In short, the goal is a holistic one: ensuring that there is variation in tonal character across all of the elements in the entire mix.

Many elements in a mix already have tonal distinction, e.g. a bass guitar vs a vocal, or an electric guitar vs drum cymbals. But the masking problems start to arise when we do two things: combine elements where parts of the tone overlap, like the higher notes of a bass guitar with the lower chords of an electric guitar, and when we start combining lots of elements in one particular range. And as mentioned earlier, the mid-range is where this typically happens. In other words, the mid-range musical elements in a mix are the ones you should be focussing on.

Image 01 - Frequency masking between electric bass and electric guitar

This example shows a single played bass note and a guitar chord occurring at one moment in time. A played note or chord consists of its fundamental and its harmonics. In this example, there is frequency masking occurring between the early harmonics of the bass and the fundamental and harmonics of the guitar. In this example, the guitar is most likely to lose clarity because its fundamental is being masked. But the masking problem is very much dependant on the level of each element in the mix.

8 Ways that frequency masking impacts mix clarity

1. An excessive number of competing elements in the mid-range.

2. Too many elements co-occurring at the same volume.

3. Too many transient elements (short percussive) occurring simultaneously.

4. Two or more sustained elements (pads, held chords on keyboards, big decaying guitar strums) in the same range cause significant masking problems.

5. High notes of one element masking the low notes of another (e.g. bass vs guitar)

6. Highly saturated elements masking everything in the same range (e.g. distorted guitars vs vocals/keyboards/horns/backing vocals/cymbals etc.).

7. Vocal clarity and annunciation being masked by drum cymbals and fizzy distorted guitars.

8. Excessive reverb and delay effects masking other elements in the same range.

In genres like rock, highly dense choruses often make it difficult to get lead vocals to cut through. Sure, you could just turn up the lead vocal level for more clarity, but heavy rock seems to sound best when the vocal sits lower in the mix. However, lowering the vocal level means they are competing more with the guitars due to their similar level.  So, the challenge for the mix engineer is to identify the areas of masking that are affecting vocal clarity and start sculpting tone of both the victim (vocal) and the offender (guitars).

Here are some ways to get the vocal to cut through in such a mix:

1. EQing out the competing frequencies of the guitars
2. Rolling off the high end of guitars to reduce high-frequency guitar notes competing with high-frequency vocal annunciation
3. Vocal limiting/compression
4. Panning guitars hard left and right away from the vocals
5. EQ boosts to improve vocal annunciation
6. Vocal level automation to momentarily raise the level of masked words

One reason that lead vocals suffer so much from masking is that they are highly melodic. As the vocal pitch moves around the frequency spectrum, it can get masked by similar sounding instruments playing in the same frequency range, such as guitars, keyboards, and horns. In other words, frequency masking of the lead vocal can vary; one moment it’s clear and defined, and the next moment it’s not. Another aspect of the voice that contributes to masking by other elements is the vast array of sounds when creating consonants, nasals, and sibilants. For example, an ‘ess’ can get obscured by a cymbal hit, and a ‘ka’ can get lost amidst percussive beats. Since the lead vocal is often the most critical element in many songs, it becomes an area of intense focus during mixdown. This is a primary reason why mix engineers can spend hours automating levels on a lead vocal, and the elements competing with the lead vocal. If you want an in-depth discussion on this topic, grab my book, Mix Automation for the Small Recording Studio.

If you’re still reading at this point, you may be feeling a bit overwhelmed with the theory. But hang in there, since there are a few simple techniques that you can use to reduce frequency masking and get the clarity back into your mixes.

10 Tips to minimise frequency masking for greater mix clarity

1. Choose combinations of musical elements with different tonal characters 

When recording guitars, use different guitars, different pickups, different pedals, and different amps. Choose vocalists with a different character to create lush and distinctive backing vocals. In my opinion, this method is by far the best approach because you start thinking about achieving unique combinations during the production and composition process. Ultimately, it makes less work in the mixing stage and can lead to significantly better sounding recordings.

2. Reduce the number of musical elements playing at any one time

Less instrumentation means more clarity and less chance of frequency masking.

3. Pan similar sounding elements apart

Panning those similar-sounding combinations of instruments apart will help reduce the masking, but any masking will become obvious again once the mix is collapsed to mono. While much of today’s music is consumed in stereo with earbuds and car radios, be aware that clubs and pubs commonly use mono sound systems. 

4. Use subtractive equalisation 

Identify the masking frequencies between two elements and reduce the clashing EQ ranges on one element. If the masking problem involves a key element, like a lead vocal, then you’ll probably want to preserve the tonal character of the vocal and focus your subtractive EQing on the other element.

5. Use different registers so that elements occupy different parts of the frequency spectrum

Before recording, a producer can get different instruments playing in a different register to make ‘room’ for a vocal, e.g. guitar chords may be played in a higher register, which can also make ‘room’ for the bass guitar. If you’re doing the wall-of-guitars thing then you can get big wide guitar-scapes with this technique, e.g. get the guitarist to play different inversions of the same chords on different takes. Playing in different registers works effectively when combining lots of midrange instruments.

6. Use volume level automation to adjust instrument levels 

Remember that frequency masking results from similar sounding musical elements coinciding at similar volumes. Use volume level automation to ‘ride up’ the volume of masked elements. This technique is perfect for any instrument or vocal in the mix, but especially useful for lead instruments such as lead vocals, lead guitar, saxophone solos. Conversely, you can get clarity of lead elements by ‘riding down’ the level of competing elements. If you want to learn more and get some essential automation skills, check out my book, Mix Automation for the Small Recording Studio. It’s available on Amazon in print and Kindle formats.

7. Use counter-rhythms for similar sounding elements

Playing with a counter-rhythm means that the timing of the performance varies in comparison to another performance. Counter-rhythms work great because the ear is sensitive to differences in timing, and these variations are a great way to create distinction between elements. For instance, if you want to make two similar sounding guitars more distinct, then play each with different timing. This approach can work miracles for an entire song because it provides clarity between the elements. 

8. Use high-pass and low-pass filtering

HPF and LPF are one of the simplest ways to reduce masking at the extremes of the frequency spectrum, e.g. try rolling off the lows on your electric guitars, keyboards, and horns at 125 Hz to minimise masking with the bass guitar, and hear how the low end instantly gains clarity. Roll off the high frequencies of distorted guitars at 5 kHz and see how the removal of fizz unmasks vocal clarity and drum percussion.

9. Identify your masking issues by listening in full range mono

Listening in mono on full range monitors helps identify masking because the stereo soundstage is collapsed, combining all frequencies that were previously separated in the stereo sound-field. If you can get a clear sounding mix in mono, your stereo mixes will be even clearer.

10. Equalise your groups

Equalising groups of instruments can considerably reduce the frequency masking broadly across the song by providing clarity between drums, vocals, keyboards, guitars, and so on. I regularly use this technique, starting with HPF and LPF adjustments, and then moving into subtractive and complementary EQing. Remember that this method is not a substitute for fixing frequency masking between individual elements, e.g. you will often need to reduce masking between individual tracks within those groups.


How do you deal with frequency masking in your mixes? Is it something that's set in your workflow or is it a new concept for you? Hit me back. Let me know what's working for you and what's not.


All the best
Amos