i'm really newbie on the topic and i was wondering what changes and where is the proper way to equalize an Instrument (e.g. digital piano, acoustic guitar) on a PA System or during Home recording. It's better on the equalize control embedded on the instrument or in the mixer? Thank you very much.
I started writing a long answer about the different responsibilities of the performer (make the sound you want the audience to hear) and the engineer (convey that sound as accurately as possible, using imperfect equipment in an imperfect space - and ALL equipment and spaces are imperfect to some extent).
But it's not like that any more. Performer, instrument and PA/recorder are parts of a system that must be aware of and accommodate each other. You all do what it takes. And that's your answer. Work together.
One point to consider. EQ can only cut or boost content that exists. If you cut the bass on your instrument to sound good in YOUR monitor, but the room is bass-light, the engineer can't put it all back.
For home recording it's generally better to get as much of the signal as possible ( without distortion ) as completely flat as you can....then use onboard or external EQ to get where you want. If you a special environment, a room with perfect ecko for example....but...what your ear is hearing and how to get that in a mic in that perfect room can be difficult. In performance...you need to have a relationship with the engineer. THEY ARE PART OF YOUR PERFORMANCE. No matter how well you sound at home, each environment is different, and hopefully the engineer knows his room....hard to tell whats coming out of the mains versus the monitors...it's trust....it's good to have a trusted set of ears in the audience...if you think your mix sounds bad and you are fussing with the eq on your guitar...its dangerous and distracting from the music your supposed to be focusing on. Good luck.
EQ should only be used as a last resort. Hopefully, the sound engineer has profiled the room they're working in, so they know where it cuts and boosts frequencies. They'll have the sound desk EQ set up to accommodate those changes.
When it's time to record, a good engineer will spend hours moving microphones to get the best signal for each instrument - and may use more than one microphone for each instrument in order to get a good selection of signals to work from (e.g front/back/inside for a Cahon, front/inside/piezo for a guitar, etc). If EQ is absolutely needed, then it should be notched as closely as possible to the offending frequency so that the sound from the rest of the instrument isn't affected.