volume +4 is it same as gain +4?

The difference between the 2 is the gain boosts the signal before all the fx and the volume boosts after all the fx.  I would suggest first mess with the gain then use the volume for minor adjustments

It's exactly the same, if you have nothing in the fx bin. If you have a compressor or other dynamics processors in the fx bin, then they are not the same. EQs, modulators, delays, etc. don't usually care as long as the gain isn't boosting so much as to overdrive them. So yes, as far as signal levels go (assuming the fx bin is at unity, i.e. no additional gain from plugins) lowering the gain by 6.4 dB is the same as lowering it by 6 dB and then lowering it an additional 0.4 dB via the volume fader.
 
But...
 
Bear in mind that what appears on the master bus is the algebraic sum of all tracks. This means that even if no track individually exceeds 0dB, the master bus can still go over 0dB. It's a good practice to keep all your tracks below at least -6 dB. I shoot for -12 dB when I can.

Sorry, that YouTube link's not working.

PsychatoR
i put the normal track who was at volume -6.4 to 0, its not clipping.
but if i put this track back at -6.4 and put the master bus (its directly linked there) to volume +6.0 and gain +0.4, it begin to clip. i have to put gain to +0.3, so now its not clipping. not sure its exactly the same level at example 1... but should be really near...

Because recordings tend to be in 24 bit, and because of Sonar's 32 or 64 bit internal processing there's so much internal digital headroom it's almost impossible to push a track (with no plugins present) into clipping, so long as the track or convertor wasn't clipping when the audio was recorded.

The master bus and the output to hardware busses are different, they will clip, as will the digital-analogue converter in the interface if it's pushed to hard. And that kind of digital clipping is the opposite of musical, it's just instant very, very loud noise. A clipping length of a few samples sounds like a click or pop, longer periods are just abrasive, grinding noise.

Once plugins are involved that can change, though plugins tend to go into an analogue-style distortion before digitally clipping, at least if they emulate anaogue hardware. So with plugins the thing to avoid is unwanted "analogue style" distortion caused by overloading the plugin's input or internal "circuitry".

There's a youtube video by James Wiltshire that's interesting concerning levels and k-metering. It focuses on Logic but it's applicable to any DAW.

https://m.youtube.com/watch?v=7WigF9IDdcQ

interpolated
I'm sure Gain is post-fader and Volume is the actual prefader volume. So whatever is set on the Volume will be superceded by the gain. It really is there for you adjust output in the mix without adjusting the contrast between your other tracks. Another reason is you might be using a Direct Monitoring setup where you a +3dB difference between your input recording and playback track.
 

You have that completely backwards. Check out page 1237 of the Sonar manual for the signal flow chart.

OK I apologise. Gain is input and comes before the Output. Can't find the manual yet though.
 
 

As soon as you mix two or more tracks, even with no effects, the maximum values will almost always hit higher peaks than any of the individual tracks.
 
Rather than sweat why this is so, your best move is to simply back off each track until all of them have peak values under -6 dB. You can do that pretty quickly: in the Track View, press CTL-A to select all tracks. Then choose any one of the selected tracks and take a few dB off its Gain slider while holding the CTL key down. All the selected tracks' gains will be reduced by the same amount, so overall balance will be unaffected but when summed they'll stay out of the red.

up?

I watched the video, but it's a little fuzzy so I had a hard time figuring out what was going on. What I see is that your track peaks at 0.0 dB before any adjustments, drops to -6.4 dB when you take off 6.4 dB via the volume slider as expected. Then you continue playback and a little further into the track, at 2:50 it goes into the red. Next, you switch the view to the master and boost both volume and gain by some amount I can't make out, and the peaks are in the red, to a value I can't make out.
 
I'm not seeing the mystery, sorry. Your track has peaks that exceed 0 dB, so adding anything at the master bus - by any means - is going to push it into the red, as your video shows.
 
Tip: play it all the way through once, then right-click on the peak indicator and select Go to Peak. This will move the Now cursor to the the highest peak in the track. This is the portion of the track you should be looping for your tests. (Part of my confusion was that in the video, you played two different portions of the track and each had different maximum peaks.)
 
Once you've identified the highest peak, reset all volume and gain sliders and play back that portion of the track. The peak indicator on the master bus should match that of the track. Now, to make that number go up by 1 dB, you can add 1 dB to any of the following: track volume, track gain, master gain or master volume. All four should have the same effect. To truly convince yourself that it's all working as expected, perform the test with a steady test tone, to eliminate most variables.
 
If all this has not just been an educational experiment and you actually just want to keep your master bus out of the red, there is but one solution: back off the gain slider on the track. That's the standard approach to mitigating an excessively hot track.
 
 

 
i didnt add anything in the master bus. but whatever i found another solution.
i will tell my friend to lower his whole song project by -5,0 and add my guitar solo i made in this sonar projet, but i think it will be a pass in ass for him to not lowering my solo guitar by -5,0 too. just all his other tracks except my solo lol
anyway he's obligated to lower volume of his whole song, if he wanna add my guitar solo.