As a studio guy I can definitely weigh in here.
What you have kind of asked here (without really knowing), is the equivalent of me as a young and green taper saying “so I have my phone microphone, how do I get a good live recording with that?” Well, for one thing that’s not the ideal gear to use - not that you can’t do it, it’s just that you’re facing myriad problems right off the get go; also, it’s not really understanding the system - different gear/mics/capsules/stereo configurations/techniques/LOCATION will all yield different results. And then, once I understand all that, I need to learn HOW to use all this gear to create a functional tape, altering my process as I learn and become experienced. Well, EQ is kinda like that - there are MANY different types of EQ, each with its own characteristics and usages; then once you understand all that, you must learn through experience how to effectively manipulate it to get the desired end product.
There is no simple way to learn or even understand EQ. There aren’t hard-set rules. Many producers like to talk about frequency ranges/bands for things like increasing or decreasing “mud”/“air”/“crunch”/etc. Sure there are some ranges where certain sounds or aspects of them like to be, but IMO that’s the wrong way to go about EQing, entirely. In my opinion it’s best to understand how to listen, and then once you’ve isolated what needs adjustment then keep whittling away til the sound after equalization is closer (or at) what you desire.
Contrary to furburger, I don’t use a spectrogram to guide my EQ usage; I trust my ears instead. But then again, I have spent COUNTLESS hours at mixing desks or with headphones on, tweaking EQs to get the sound I want. It’s really one of those things that comes with experience and practice, but it requires assloads of both to understand - and then fluidly control - how to use an equalizer. That said, I’ll agree with furburger that MANY people don’t know what they’re doing, and can/do make recordings worse by using EQ to detrimental effect.
If you REALLY (and I mean REALLY) are wanting to understand EQ, there are two steps I would take if I were you:
- Get yourself a copy of FabFilter Pro-Q 2. In addition to LOADS of features that are useful and will be helpful down the line as you learn EQ, it has the particularly nifty feature of being able to isolate any band that you are actively manipulating, and it can solo that band while you sweep its frequency and Q/resonance in real time. This is really useful in training your ear WHAT to listen for, while also making the job of HOW to EQ easier - once you know what you want to adjust.
- A VERY general rule when using an equalizer is: if you need to boost, do so with a VERY broad resonance, and no more than about 3 dB or so while you are still learning how to use it. If you are cutting, either use equally broad and gradual shifts, or if you need to cut out a problematic frequency, do so with VERY high Q and at extreme gain reduction. The soloing band feature in Pro Q 2 is great for this as you can vcreate a resonant bell filter, set its gain high, solo it, and sweep until you find the trouble frequency.
If you have further questions about any of this stuff please feel free to ask here or by PM if you prefer that.