i always read the rms should be somewhere around -18 and -20. how come when i'm around -12 and -18 dbfs the rms is so low when people recommend record at those levels and then says "the avergae level should be about "-20dbrms"
The thing to remember about average or RMS values is that they depend entirely on the density of the audio signal itself. Think of it this way:
If you recorded a metronomic click track that clicked twice a second, evem if the click value was all the way up at 0dBFS (maximum) the average or RMS value would still be waaaaay down in the cellar. I'm not sure of the exact value (anyone care to try it for us?), but it'd probably be below -20dBFS, even though the peaks are all the way up at zero. That's because the average value is actually closer to silent, because most of the time the signal actually is silent.
On the other hand, if you have a wall of guitar distortion at feedback run through heavy compression, even if you're only peaking at, say, -12dBFS - 12 dB lower than the click track - the RMS value could easily be above -20dBFS, and possibly as high as -14 or -15dBFS. Because the average signal level is much higher.
I think those that told you that a peak level of -12 to -18dBFS would yield an expected RMS level of -20dBFS were probably used to seeing headbanger-class dynamics; i.e. flat as a pancake. If you're doing a different genre of music (and if the "dj" in your handle means anything, it's probably hip hop, but it would be just as true for many flavors of jazz, folk, pop, classical, country, etc.), the difference between your peaks and your average* are probably going to be much greater, and that is normal.
*that difference between the peak and the RMS values is called the "crest factor", BTW.
G.