Everyone who mixes music has encountered this at some point... Two instruments seeming to fight with each other in the mix, struggling to find their own place. The reason behind this battle is 'auditory masking.' A phenomenon where specific frequencies obscure each other. Unsurprisingly, this masking or overlapping occurs among instruments that share the same or similar frequency ranges.

Instruments Where Frequency Clashes Frequently Occur

Let's take a look at the instruments where frequency clashes frequently occur:

• Kick and bass: The classic duo! The kick drum and bass guitar often share similar low-frequency ranges, which can lead to them masking each other in the mix.

• Vocal and piano: Since vocals tend to concentrate in different frequency ranges depending on the singers, it's essential to carefully monitor whether there is any frequency clash with the piano, an instrument with a broad frequency range.

• Vocal and guitar: As mentioned above, vocals can concentrate in different frequency regions depending on the singer. Likewise, guitars generate distinct resonant points in the frequency spectrum based on their type and body construction. In many songs, the guitar is as crucial as the vocals. Therefore, it's critical attentively checking for any frequency clashes between them.

• Bass guitar and electric guitar: Even though the bass guitar plays in the lower octaves, the upper harmonics of the notes can overlap with the guitars.

• Electric guitar and electric piano (Rhodes, Wurlitzer, etc.): Both electric guitars and electric pianos can occupy similar lower mid-range frequencies, resulting in a muddled mix. 

• Electric guitar and trumpet: Electric guitars and trumpets may have overlapping frequencies in the mid to high range, potentially causing them to mask each other. 

• Acoustic guitar and hi-hat: Especially in acoustic guitars played with a pick, there can be frequency clashes with the hi-hat.

• Similar synth sounds: Frequency clashes and masking between similar synth sounds are ubiquitous. Problems get worse when more than two similar-sounding synth patches are stacked on top of each other.

Methods to Prevent Frequency Masking in Your Mixes

Let's move forward with suggestions as to how to effectively reduce frequency masking in your mixes:

1- Arrangement

The mix starts with the arrangement of the song! If there are problems in the musical arrangement of the song, achieving a successful mix can become challenging, if not impossible. Mix engineers and arrangers with good working relationships can make adjustments to the arrangement during the mix stage. When the mix engineer encounters issues like frequency masking or instrument overlap, they provide feedback, and the arranger can consider changes to the arrangement based on these recommendations. 

2- High-Pass and Low-Pass Filters

In music mixes, instruments often produce sound across a wide range of frequencies. However, for a balanced mix, we don't always require all those frequencies. To avoid conflicts between instruments, we can use low and high pass filters to exclude unnecessary low or high frequency content from each instrument. This approach helps prevent potential frequency clashes and can produce a cleaner and more distinct sound in the final mix.

3- Frequency Carving with EQ

To avoid frequency clashes in a mix, we can employ a ‘frequency carving’ technique using a parametric EQ.

For instance, when both the kick and bass guitar have significant energy at 70 Hz, they can mask each other, causing muddiness in the mix. To address this, we can take the following approach: boost 70 Hz in the kick and 100 Hz in the bass guitar, giving each instrument a different frequency emphasis. Furthermore, to prevent these frequency ranges from clashing, we can reduce the corresponding frequencies in other instruments. In other words, if we boost 70 Hz in the kick, we can attenuate 100 Hz in the same kick, and vice versa for the bass guitar. This way, we achieve better separation between the instruments and create a clearer, more balanced mix.

4- Using the Sidechain Compression Technique

Another effective method to prevent instrument masking is using the sidechain compression technique.

For instance, let's consider a track where guitars play a prominent role, and you want to create space for the trumpet to be heard clearly. In this case, you can group the guitars together and apply sidechain compression. When the trumpet plays, the sidechain compression will slightly reduce the level of the guitar group, allowing the trumpet's sound to come through more prominently. This technique helps maintain clarity and separation between instruments, ensuring a more cohesive and polished mix.

5- Dynamic EQ

In some cases, traditional approaches, such as using an EQ or compression, may not provide the desired results for preventing frequency masking. That's when the dynamic EQ comes into play.

Let's consider a typical scenario where the bass guitar and kick are masking each other. Applying EQ to the bass guitar channel to highlight the kick can negatively affect the bass guitar's tone. To address this issue, a common technique (which involves using a compressor on the bass guitar channel and routing the kick's signal to the compressor's sidechain input) is used. Every time the kick hits, the bass guitar's level is momentarily attenuated, preventing auditory masking.

However, there is a problem with this approach: Each time the kick hits, all frequencies of the bass guitar are attenuated, affecting its overall sound. Instead, a more precise solution is to use dynamic EQ on the bass guitar and trigger it with the kick signal via its sidechain. This way, every time the kick hits, only the specific frequencies that clash with the kick are attenuated in the bass guitar. This fine-tuned approach allows for instrument separation and, at the same time, preserves the bass guitar's tone.

6- Special Plug-ins

Certain plug-ins come equipped with advanced algorithms and features that automatically detect and address frequency masking issues. One such plug-in designed specifically for this purpose is Wavesfactory Trackspacer.

To tackle frequency masking, you can insert Trackspacer on the channel of one of the instruments. By "feeding" the other instrument to Trackspacer via sidechain, the plug-in analyzes the signal at the sidechain input and intelligently applies a reverse EQ curve to the channel where you inserted it. This results in reducing or eliminating frequency masking, effectively resolving the problem.

Similar functionality can be found in other plug-ins like FabFilter Pro-Q 3 with its "collision detection" feature and iZotope Neutron 4 with its "unmask" capabilities. These special tools help audio engineers to automate the frequency management process, leading to clearer mixes with minimal manual intervention.

7- Pan

You don't always need EQ, sidechain compression, dynamic EQ, or special plug-ins to prevent frequency masking. Sometimes, many issues can be resolved by distributing instruments in the stereo panorama.

By adjusting the panning of instruments in the stereo field, you can reduce clashes and create a well-balanced mix with a sense of spaciousness. Panning allows you to position each instrument in its own distinct space, minimising frequency overlap and enhancing sound separation. However, being cautious with panning extremes is crucial, as an overly wide stereo image can lead to an unstable mix. Finding the right balance in panning can significantly contribute to preventing frequency masking in your mixes.

On a related note, you may find my article "The Difference Between Stereo Pan and Stereo Balance" informative.

If you require more advanced panning options, consider exploring frequency-based panning. It is an innovative technique that allows you to pan a specific frequency range of an instrument, offering greater control over the mix and further reducing the potential for frequency masking. Here's more about it: "What Is Frequency-Based Panning?" 

8- Saturation

In combating frequency masking, another valuable tool in your arsenal is saturation. Saturation and distortion can enhance the harmonic content of a signal, offering a way to address masking issues between instruments.

When dealing with two instruments that may be masking each other, applying saturation to one of them can add richness, especially in the upper-mid frequencies. As a result, the saturated instrument gains more character and stands out from the other, leading to improved separation in the mix.

By using saturation strategically, you can give each instrument its unique sonic space, reducing the likelihood of frequency clashes and achieving a more defined and well-defined mix. It's essential, however, to exercise restraint and moderation while applying saturation, as excessive use may lead to unintended artefacts and muddiness in the overall sound. With careful application, saturation becomes a valuable tool to enhance harmonic separation and create a more sonically appealing music mix.

Here are some recommended free saturation plug-ins:

• Klevgrand FreeAmp

• TBProAudio GSat+

• Kit Plug-ins Burier

In Conclusion

The methods and tools discussed above offer powerful solutions to tackle frequency masking problems that often arise in music mixes. By implementing these techniques, you will have the means to transform your mix, enhancing its clarity and separation to achieve a more refined and professional sound.

Embracing filter and EQ adjustments, dynamic EQ, sidechain compression, special plug-ins, and thoughtful panning allows you to sculpt each instrument's space, minimising clashes and creating a harmonious blend of sounds. Moreover, the judicious use of saturation and distortion adds richness and character, enabling instruments to stand out and find their unique sonic presence.

Happy mixing!