Try using ReaEQ on your master FX and give your mix some bass. I think people often relate warmth to bass but without realizing it.
it is important to note that too much bass is inherent in many home mixes---- low frequency and sub-harmonic buildup makes a recording sound muddy and dull, can produce strange distortions by drastically reducing headroom (even if you cant hear the offending frequencies), and generally just sounds like ass.
i will go out on a limb and say that 95% of the time, adding low frequencies is NOT going to warm up a mix.
FWIW, and YMMV.
midrange, OTOH, can really open up a recording. again, a lot of home mixes seem to celebrate the smiley-faced eq curve, whether intentional or not. not enough mids sounds distant and muddy, like a blanket over the monitors. i would try CUTTING low end and perhaps even implementing a high pass filter around 30hz.
of course, "warmth" is a very subjective thing, and could be attributed to many things--- mic/pre colorations or inadequacies, distortions and compression, saturation, etc, etc. lots of lower end mic/pre combinations are extraordinarily "sterile" sounding to my ears when recorded flat and dry.
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