Sonar 8.5.3. I've got the song peaking above -12 in the master bus, sometimes a tad into the red - but when I mix it down and play it with VLC Media Player, it seems ridiculously quiet. I've got VLC volume at 100% and if I play any song by another artist, it's plenty loud enough!
 
The waveform on the clip just touches the boundary, MPL1 Pro says the level is around -12, Cakewalk Analyst shows the occasional brief peak above -12. Sonar and plugs in Sonar seem to show that everything is fine. Could it be that VLC is using a different audio driver? How would I find out?
 
Any suggestions are much appreciated!
 
Thanks - rev

Ah, the age-old question. In a nutshell:
 
-12dB is 1/4 the amplitude of 0dB, and power, which is roughly proportional to perceived loudness changes as the square of the amplitude. So, all other things being equal, a signal peaking at -12dB is going to have 1/16 the loudness of a signal peaking at 0dB. But all things are not equal because those commercial recordings you're comparing to are using compression, limiting, EQ an other tricks of the trade to increase the RMS power while limiting the peak amplitude.
 
So basically you need to need to use a combination of gain, compression, and limiting to get the peak up close to 0dB (no more than -0.3 is advisable if you intend to export to MP3), and raise the power level. And look into EQing out the frequencies that add a lot of energy without contributing to loudness in the range where humans are most sensitive to it.
 
But first, do some Googling on Mastering and Loudness Wars.

Perceived loudness comes from the RMS of a song, not the peaks.
 
So yeah, read up like brundlefly suggests

Trouble is, I believe I've done all that. MPL1 Pro is a look-ahead mastering limiter and its display is in RMS and as mentioned, everything is fine inside Sonar. In fact, it's blowing my head off! So what's happening (or not happening) in the mixdown process?
As soon as I mix it down I have to crank the headphone amp and VLC's volume just to get it reasonable. 
I'll go back and wrestle with it as you guys suggest - what tools are you guys using in the master bus?
 
 

check the Windows Volume Mixer setting when VLC is running

Sorry, I should have Googled MLP1 Pro before posting; you're use of 'peaking' threw me off. So I gather MLP1 is showing you RMS amplitude is around -12dB, which is typical of a signal that peaks at 0dB, and hasn't been absolutely crushed with compression to get the power up. The first question then is what choices are you making in the Export dialog? And if you import that exported file back into the project to a track that goes directly to hardware Main Outs, does it sound as loud in SONAR when you A/B against the live sound on the Master bus (group the track and bus mutes in opposition). If it does, check whether you might have pulled down the Main Out volume at some point, and were making it up with monitoring amplification.
 
When preparing to export, I like to bounce a copy of the Master bus to a 'Master Bounce', using source = Buses, that goes direct to Main Outs as described, A/B (or invert phase to check nulling) against the live Master bus to make sure everything is right, and then export that 'Master Bounce' track. An incidental benefit of this is that you automatically have a copy of your 'Master' preserved inside the project for future reference, and you can make additional bounces to new lanes of the 'Master Bounce' track as needed when you re-mix.

My master limiter,  the BT Brickwall,  I set at -0.4 db. I know that's un-orthodox.  
It seems to work and all my tracks when checked will show as peaking at -0.4 
But then I check for Average RMS level with Wave Lab. Generally they will all be in the ballpark of -14db Average RMS. They stand up to all commercial music. If a song is peaking at -0.4 but is only say -16 db average, then I need to go back and re mix and look for what is peaking.  This will often be a snare drum that I need to tame. 
I also pay real close attention to the low end. Too much low end will peak your meters and kill everything else. 

revnice1
Trouble is, I believe I've done all that. MPL1 Pro is a look-ahead mastering limiter and its display is in RMS and as mentioned, everything is fine inside Sonar. In fact, it's blowing my head off! So what's happening (or not happening) in the mixdown process?
As soon as I mix it down I have to crank the headphone amp and VLC's volume just to get it reasonable. 
I'll go back and wrestle with it as you guys suggest - what tools are you guys using in the master bus?
 
 

Also check the fader level of your master buss & main outs before exporting.
They should both be at 0dB

Thanks to all your contributions, I'm doing a lot better with this problem. I pretty much followed everything all of you suggested and I'm reluctant to fess to my own stupidity because I hadn't checked some simple things that some of you mentioned. One of them I will mention is scook's suggestion.
 
100% in VLC Player is NOT 100% in the Windows Mixer, that made a lot of difference and I hadn't thought to check it. Thanks for that one dude.
 
I have Wavelab too and that helped. I was going nuts so I very much appreciate all your help!
 
rev