1K is where your main (most important) sounds should be fullest, this would usually be your leads or vocals, or mid-range bass sounds if its more of a neuro type track
have to disagree with magatu i'm afraid, unless pads are the main feature of the track, generally they will occupy the space above and below the leads or vocals (or if its a very bass orientated sound, then the mid-range bass), same goes for percussion, the snap of percussion comes in around 3-5khz, the body lower down, depending on the sound - its important not to over-fill the 1Khz zone, that is the freq at which our ears are very sensitive, so this is the range that you need to ensure that your important sounds have as much space as possible; most of my pads will have that region reduced in volume, and if its a vocal track, pretty much all my sounds, including the perucussion will have a big chunk taken out @ those freqz
if you are finding that those range of freqz are weak, its most likely because you have to much going on there, which means you under-compensate by turning down the important stuff like leads...get your other sounds to fill the spectrum where its important for them to do so, and give your leads free reign over the 1Khz range
All kind of leads and synths that contain either saw or square waves. Snare, percussion, mid bass. That´s basically it. Agree with miszt, you don´t want to have a mess in this region, generally decide on one main element(melody, bass) that contain those frequencies and build your track around it. This element should be the center of your track so make it shine.
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And try to creatively use white noise if you find that tracks sound dull and empty.
I'm surprised someone has a problem of filling that range, I always end up having a big frequency spikes around 600-1000Hz and 1000-2000Hz, coming from midrange bass/lead/synthesized stuff having fundamental frequency and 2nd harmonic harmonic sitting there.
its easy to fill the mid-range with spikes, but that doesn't necessarily mean the mix is properly balanced, or that the mid-range sounds full and fat....i noticed on a previous thread you said you find yourself wanting to add more sub and shineyness to the top end quite often, and this may well be the reason why...
when i switched to engineering as a job, the most important thing I think i learnt, was that its almost always better to turn things down, rather than turn things up - when the sub sounds too quiet, consider if the midrange is too loud, and vice-versa...