Understanding Compression and Frequency Density

Understanding compression can be immeasurably complex and even more challenging to instantiate effectively across your production. Therefore, developing a practical approach which is well-considered and based on traditional theory is essential.

One significant aspect of compression is understanding that the process increases the frequency density of a sound, much like compressing the air inside of a beachball down to the size of a grape. The amount of air inside the grape remains the same, yet its density has significantly increased. Compressing a sound increases its frequency density and solidifies its imaging in the 3D sound field. When a sound is dense, it will generally psychoacoustically image better in the speakers. When a sound lacks density, its imaging characteristics will be unclear, and the sound will lack focus and clarity.

Although this generally remains true, a sound can also become too dense, eventually smearing its imaging in the speakers. Thus, our processing must always work towards solidifying the psychoacoustic imaging of a sound.

Additionally, analogue compression adds saturation to a sound, increasing its frequency density by imparting harmonic distortion characteristics with different tonal densities across the frequency spectrum. It is these individual tonal density characteristics which make each processor unique. For example, some processors may add more frequency density in the low mids of a sound, adding warmth and character. Other processors may have lush density characteristics in the upper mids adding more presence and focus to a vocal.

It is our job as engineers to choose processors that help aid a sound in its deficient frequency zones by adding density characteristics in the areas lacking the most. If we choose a processor which is density rich in frequency zones which are already plentiful, we will only add to the tonal imbalances of a sound. Yet if we choose a processor rich with density characteristics that fill in the sonic holes of a sound or mix, we help solidify its imaging and fill in its deficient frequency zones.

This fundamental principle becomes even more vital when choosing a compressor for your mix bus, as you can easily smear the imaging of your entire mix by selecting the wrong processor. Choose a compressor which brings your mix into focus and helps solidify the individual placement of each sound within the 3D sound field.

Lastly, it is best to achieve a sonically dense sound with gradual, cumulative processing rather than pushing any one processor to fair throughout the mixing process. For example, you may gradually increase the frequency density of a sound using modest amounts of several processors, such as Microphone Preamplifiers, Analogue Equalisers, Analogue Compressors, Tape Machine units and other vintage processors which impart subtle compression or saturation characteristics. Cumulatively adding density tends to sound more natural and helps maintain the organic integrity of the original signal by treating the audio more gently, slowly bringing the sound together one layer at a time. However, it is essential to mention that this is only sometimes the case, as more heavy-handed processing is occasionally necessary to bring a sound together, often employing techniques such as parallel compression.

Although this may appear complex, successfully applying this principle to your workflow will considerably improve the quality of your mixes and bring each instrument into focus. Always be mindful of whether a processor smears or solidifies the imaging of a sound or a group of sounds in a mix.

Jamie Hall – Hall Audio Dynamics

8th December 2022