When it comes to EQ’ing keys, there is a big difference between what you will do for electronic keys/synthesizers and acoustic pianos. So, let’s go through both.
Keys & Synthesizers
Electronic keys don’t often need a lot of EQ, but you can fine-tune the sound by adjusting a few fundamental frequency ranges.
Tip: Clean up the mudiness.
Keys and synths can get a bit muddy in the 400-600Hz range. Use a peaking filter with a Q value around 4 in this area to clean up the sound, especially when it is layered with other instruments.
Tip: Help the keys ‘cut through’ the mix.
If you need the sound to cut through the mix, try boosting slightly in the 1-2 kHz range. Or, you may even need to cut this area to make room for other instruments.
The 3-4kHz range is where the the primary presence and clarity can be found. Boost this area a little if necessary. Or, you can cut this area to make the tone a bit darker.
Regarding pianos, there are many different types and sizes that will have a range of tonal properties, so these tips will depend on size, playing style and miking techniques.
Tip: Cut the boominess.
Pianos can tend to be really boomy in the 100-200Hz range. The best way to fix this problem is with a low shelf filter at about 200Hz and cut 3-6dB.
This can also help reduce feedback or other low end resonance from drums or nearby instruments on stage.
Tip: Brighten the tone of the piano.
You can brighten the tone and help the piano cut through the mix by using a peaking filter in the 3kHz range with a Q value around 4 and applying a slight boost.
Keep in mind, too much emphasis in this range can exaggerate distracting elements like damper and string noise.
Experiment with the Q value.
When you are dialing in EQ, don’t forget to experiment with the Q value. A lower Q value will give you a smoother frequency response and blended tone, whereas a higher Q value will give you greater control over the frequencies that you do and don’t want to cut.
It just takes a bit of time and close listening to find the sweet spot.