If you’re trying to make a clean mix, pay attention around 150 to 250Hz. Use an eq to attenuate the region, or reduce warm tube or other warm saturators to make the mix sound cleaner - additionally, in-time effects, bass ducking, and other techniques help create a clean mix.
Although this seems a bit basic, take a serious look and listen to your low-mids if your mix isn’t sounding clean. Odds are you have multiple instruments competing for limited space in the low-frequency range, resulting in clashing and a muddy unbalanced sound.
The first step would be to check out your kick and bass, and attenuate areas that overlap - then move on to guitars and vocals.
If after equalizing your low mids you still have a muddy sound, take a look at which saturation types you’re using - if you’re using a warm tube of transistor option, this may be causing the issue. Since these create a strong second-order harmonic, this may create muddiness.
Instead, try tape or clean tube settings, or maybe an exciter, to create higher-order harmonics.
Again, kick and bass instrumentation overlap can be a problem - you can use an external side chain setting to remedy this. Place a compressor on your bass track, and side-chain the kick - this way whenever the kick hits the bass track is attenuated, carving out more room for both.
Try this in combination with other tips listed here for a clean low-frequency range.
Disharmonious notes can make your mix sound less clean - to fix this find the key of your mix and subtly amplify in keynotes. For example, if my mix is in the key of D major, I can boost all D notes with a preset we created.
This makes the fundamental and harmonics of the mix stick out a little more.
Low-level compression is great but it can bring up unwanted noise - since it amplifies from the noise floor up in most plugins. To fix this, first use a gate on the instrument you want to upward compression, to attenuate the signal whenever it falls below a certain level.
After the gate, insert your low-level compressor to achieve the effect without unwanted additional noise.
I’ve mentioned this a couple of times before but if your mix isn’t sounding clean, do some much-needed edited via clip gain. For example, if your vocal’s dynamics are inconsistent don’t compress heavily to make it all uniform - use clip gain and create a consistent performance.
Then introduce your processing. Since clip gain comes before all processing, it's a great tool for establishing dynamic control.
In time effects can take a mix that sounds cacophonous and turn it into one that sounds ordered and controlled. For example, if my BPM is 120 and my reverb time is 620ms, this length isn’t a note - 500ms is a quarter note, 1000ms is a half note.
But 620ms doesn’t fit. To find note-based times for your reverb, delay, or even your compression, take 60000 and divide it by your BPM.
This one may be more of a preference on my part, but I’ve noticed if I distort the image’s mids but keep the sides clean, this creates a louder, but cleaner sounding mix. Distortion on the sides seems to have too great of an impact on the image’s timbre.
Instead, I’ll just boost these with an EQ or other mid-side processor.
I’ve stated this before, but I wanted to show it with some metering in this example - in short, delay-based stereo images will affect your image’s phase significantly. Mid-side processing lets you achieve a wider image without excessive changes to your image, establishing a wider but in-phase signal.
With a correlation meter, we can observe our original signal, our signal after delay-based imaging, and our signal after mid-side imaging.
Notice how the correlation meter is similar to the original and mid-size but varies significantly when using the delay-based imager.