BASSIC Productions
I am surprise at the amount of -0.3dB posts unless we aren't discussing -0.3dBfs.  I think people are misinterpreting dBfs, dBspl and dBu with dynamic range of audio recording, editing, mixing and mastering levels.  We need to keep in mind that a Decibel (1/10th of a Bell unit) is actually a ratio of two pieces of information... typically, this is a reference value of strength to a perceived value of strength.  In a sound file, this is the signal level compared, in a ratio, to the perceived volume... which also includes an ability to measure the dBspl of the presentation venue and the Fletcher-Munson curves to evaluate perception of the presentation venue.
 
If one masters to 0 thru -6dBfs, the resulting sound at theater volumes of 110dBspl will mean the entire sound will be 110dBspl to 104dBspl (this would be so loud you will get nauseous!)  Even lowering the DNR to 96dBspl will be amazingly loud in a film.  For a DVD, this would be fine... in an internet music presentation, this will mean some sounds are loud and some are too soft to really hear on a laptop speaker system.
 
I have found the best mix/mastering technique to allow for a 24dB DNR for modern sound.  A little bit of compression can the be used to master for various presentation requirements.  For some, specific requests, I have mastered to a 48dB DNR... but you can still compress at 2:1 to get back to 24dB DNR without compromising the basic sound.

I master to 0.3 db PEAK all the time.
However that's not really the important thing in mastering to me anyway, RMS is.
I shoot for between -8 to -12  RMS but am always hanging in around -9.
 
Mastering is something that takes years to polish the craft.
Back in the day I would simply throw some limiters in the master bus and start some vigorous knob turning.
Its still a craft I get better at over the years, with new tricks, new methods. I only do audio, never DVD, soundtracks. I have found over the years, the best way to get better at it is to try new things, experiment.
It takes you down new roads, trying an unorthodox style, something different. I approach songwriting the same way.

BASSIC Productions
I think people are misinterpreting dBfs, dBspl and dBu with dynamic range of audio recording, editing, mixing and mastering levels.  

Yeh, I used to master to -0.3 dBSPL but found it was a bit too quiet. 
 
Actually, I'm pretty sure most folks here understand that decibels are ratios, and that "fs" is implied when talking about limiter settings. Although dynamic range is certainly relevant, it's only tangentially related to peak limiting. 
 
 
 

This excellent topic has awakened a need to deepen my knowledge about audio.
For those who wish the same, I found an excellent beginner course: https://www.macprovideo.com/tutorial/audio-sound-basics/
 

Thank you for a lot of good and interesting information. I sometimes have a few high peaks but relatively low RMS. I've tried a variety of compression tricks to increase RMS but have had no general success.
 
Q: Any guidance on increasing RMS while only gently compressing the peaks? I do recognize that the peaks, in relative terms, need to get smaller.
 
I've tried Kotelnikov with some success, but I was hoping the Cakewalk collective had this one figured out :)
 
Thanks in advance
 
Allan
 
 

AllanH
Thank you for a lot of good and interesting information. I sometimes have a few high peaks but relatively low RMS. I've tried a variety of compression tricks to increase RMS but have had no general success.
 
Q: Any guidance on increasing RMS while only gently compressing the peaks? I do recognize that the peaks, in relative terms, need to get smaller.

 
Unless you really want to reduce the peaks, a limiter is probably the tool of choice. But the other thing I do (and recommend only to those with infinite amounts of patience) is isolating the rogue peaks and reducing their levels, so everything else can be brought up without needing to use dynamics. 
 
For example if most of a mix’s peaks reach –5 dB but a couple dozen go to –1 dB, I’ll normalize just the half-cycle of those couple dozen peaks to –5 dB. That way I can raise the level 4dB without having to use dynamics processing.
 
I do participate in the loudness wars, but as a conscientious objector . I slam my own material pretty hard these days because that's the kind of material I do, but I'm working on some newer, simpler songs and dialing back on the slamming. As to clients, I give them several options and let them choose what they want. I'm mastering an album project by Bryan Ferry's lead guitarist and he's great to work with, he doesn't want it slammed and wants everything articulated well. I recommended what I thought worked for his music, and we were exactly on the same page...I love it when that happens.

BTW I think it's worth mentioning that (x number of dB) x 6 is only an approximation of the dynamic range. It gives you the amount of calculational dynamic range when doing math within a DAW, but no converter delivers on the spec. The last bit is always dithering so it doesn't have a clue anyway, and inaccuracies in chip trimming, circuit board layout, noise, etc. degrade the S/N ratio. In the real world, you can count on a 24-bit converter to give 20 bits of "real" dynamic range, although that can be less or more depending on the gear. 
 
 

-0.1 on my Master Bus with my Fabfilter Pro-L Limiter set to 0.0