Earlier I defined the mid frequencies as the ones between 600 and 1200 Hz. These would contain higher portions of the harmonies, higher melodies, and a whole bunch of harmonics.
For most of music history, solo singers who could sing very high were coveted. Coloratura sopranos and castrato singers were great assets because their voices could soar audibly above the rest of the orchestration. Their vocals pierce because the sit above the normal range for the rest of the instruments. This frequency bandwidth aligns pretty well with the upper reaches of the soprano voice and the high-flying notes of 80s lead guitar.
Now accompaniment instruments such as guitar and piano might also play in this register in band situations, however in this range the emphasis tends to be on notes other than the root or melody. This allows the soloist or lead instrument to have the spotlight in this frequency band.
This is also the register where the frequency range starts to increase. Previously, we were dealing with relatively small increments between notes and registers, but here we have a gamut of 600 Hz as opposed to the low-mids which were only 300 Hz. This allows much more room to play with sonics using EQs, harmonic exciters, and other effects which is great because this section houses most of the lower order harmonics other than the fundamental.
As mentioned in the primer, harmonics help us distinguish one instrument from another. Even harmonics give a warmer, organic, and natural sound while odd harmonics impart a more harsh and metallic sound. Smooth guitars through tube amplifiers have rich even harmonics while harsh distorted heavy metal guitars have more odd harmonic content. Brass instruments have more of an emphasis on odd harmonics while strings have more even harmonics.
So now going back to bass instruments like the kick and bass guitar, another good way to distinguish them from each other is by treating their harmonics in this range differently. This range is better for this kind of treatment because it avoids putting the changes intended for emphasis in the frequency band with a lot of build-up like the low mids. This range contains mostly harmonics and solo instruments, so there isn’t a lot to get in the way of hearing these subtle alterations and they are still low enough to be significant to the fundamental sound.
So if we have a bass guitar playing mostly root notes down in the key of A, we’d know that the bass is playing notes in the frequency range of 55-110 Hz. This would mean second harmonics from 110 to 220 and third harmonics from 220 to 440. These are great to try and treat, especially if you are dealing with sparse mixes, but they aren’t really helpful in densely orchestrated tunes because other instruments will be taking up those frequency bands. The next harmonics would be from 440 to 880. These harmonics are in this frequency range, so a nice wide EQ centered at 660 and subtly boosting around might give the bass the audibility you need and it would be nice and smooth since it emphasizes the even harmonic (4th). You could also try and emphasize the next batch of harmonics which would be 880 to 1760. This would put the center right at 1.2 KHz, right at the top of our range. And this would impart a more harsh and aggressive tone.
You might de-emphasize those frequencies in the kick drum or even choose to emphasize frequencies that fall on the outskirts of bass guitar’s harmonic ranges. If you find that the bass rarely sounds harmonics in the 900 range, it’d be a perfect place to emphasize the kick drum and maybe carve out the bass there. All you need is a little spot in the mix for your ear to key on and you’ve got audibility.
Now the bass guitar I’ve used in my example is 1-2 octaves below the other non-bass instruments I’ve talked about in my hypothetical mix. That means that treating these instruments in the mid-range will be emphasizing lower order harmonics and can really alter the instruments’ sounds. But you do have a nice wide range to work with, so treating each instrument individually with a different portion of the bandwidth for emphasis can help benefit audibility. Plus, this is where many of the sounds intrinsic to specific instruments exist, so emphasize the frequency band that makes a trumpet really sound like a trumpet can help to keep it audible but prevent it from overtaking the lead vocal.
One thing I want to emphasize here is that most instruments play a range of notes, not just one note like a kick drum. In the bass guitar example, you saw how wide a range a bass guitar’s frequency content can have from just playing in one octave. I didn’t give any specifics about the tune other than the key, we don’t know how often it plays what note or which note, we just know the key. Many experts and magazines will like to give you helpful frequencies to try when mixing. Bear in mind that these are only guidelines and could not possibly be a one stop fix for all mixing needs. If somebody tells you to cut 450 in every instance to make a mix better, it would really be a shame for songs in the key of A whose mid-range instruments would be getting de-emphasized when they play the root note…