There’s a reason certain things sound good. There’s a reason many people play Stats, Teles, Les Pauls, SGs, and Martins – even though some of these guitars can be clunkers. There’s a reason ’60’s Ludwig drums are still around. There’s a reason people have real pianos and organs at studios even though keyboard modules stay in tune easier and are cheaper. There are no quick fixes. There is no box that will make a crappy instrument have great intonation and perfect action. There is no computer plug-in that will make your poorly-tuned drums sound in tune.
I was working on an album recently where we had five snare drums, several ride and crash cymbals, four or five electric guitars, two guitar amps, three bass guitars, two bass amps, four acoustic guitars, grand piano, Rhodes piano, Hammond C2 with Leslie and some synths. I realized that even on a budget much of this stuff could be borrowed from friends (maybe not the grand piano) and that the options available were lending different sounds and feels to the songs, which was a very important thing. These were things that all the mics and preamps couldn’t change – they have to come from the source.
Before the mic, preamp, compressor and recording device comes the instrument. Make sure it does what you think it does and want it to do, and that you have other options available. You’ll make a better record, I guarantee it.