Twice I've used the Channel Tools plug-in to alter a track (eg. remove lead vocals) and upon exporting the project - and playing back through my iPhone's mono speaker - the track with the CT plug-in is silent as a fox!

I would turn the Mid-Gain all the way down and that's all it takes.

What sorcery is this?! Could some smart people explain to me what it going on here?

I'm going to guess that the resulting "side" signals right and left channels are the same data, but 180 degrees out of phase with each other.  When summed to mono, you would then get...nuthin'.
 
Again...guessing...but you could probably mitigate that with another instance of channel tools (downwind of the first one) to flip the phase of one channel.

I have not tried this but this is what I think is happening.
 
Chanel tools converts L+R into a Mid and Side signal. where Mid = L+R and Side = L-R. Then it converts the Mid and side back to L R by doing L = Mid + Side, R = Mid - Side. So if Mid is turned down all the way all you get is L = Side and R = -Side. So if you sum L and R you get L + R = Side = Side = 0.
 
 

Yes, I think we need more details on what you've got going on in the project and what you're doing with Channel Tools. And are you exporting to mono wave, or letting your iphone sum the two channels - or maybe it only plays one channel of a stereo wave by design...?
 
I don't really see how turning MIDI Gain (a.k.a. Velocity Offset) "all the way down" would mitigate the problem since you'd effectively be silencing the MIDI events. Unless maybe there's cancellation going on between live MIDI-driven synths and bounced audio tracks...? Scratch that that mis-read. 
 
Too many unknowns.

brundlefly
 
I don't really see how turning MIDI Gain (a.k.a. Velocity Offset) "all the way down" would mitigate the problem since you'd effectively be silencing the MIDI events.

I think the OP was talking about the "Mid" of Mid-Side.  You can do a quick and dirty karaoke/music minus one/vocal cancel trick just by doing a Mid-Side treatment and killing the Mid channel.  That eliminates anything that's equal in both channels.  Since most vocals are panned dead center...the vocal will go away.  (That's probably also true for the bass and kick...for the same reason.)

dantarbill
 

I think the OP was talking about the "Mid" of Mid-Side.



Ha! Duh. Of course. Neeevermind.
 
 

reginaldStjohn
I have not tried this but this is what I think is happening.

<snip>

That makes sense. If the original stereo source pair of tracks had everything simply panned down the middle, making it effectively mono with the same data in L and R, then after splitting to mid/side taking out the mid content by reducing its volume would result in silence when processed back into stereo.

If the original source was a mono track, again doing a mid/side split, removing mid and then reconstructing back to mono or stereo would result in silence. Again, I think. Would have to try it to be certain and it's late here.

Other than that, more information about the original audio track(s) and the format at the end of the process is needed.

Ok...I checked it out with a stereo mix and two instances of Channel Tools (CT) in series (hosted in WaveLab) with Steinberg's Leveler plug at the end of the chain...
 
The first CT instance encodes Mid-Side and pulls the Mid gain down to zero.
At this point, the phase scope shows a horizontal line, indicating that the right and left channels are completely out of phase.  You'll hear this as a kind of cockeyed stereo image when under headphones.
 
Let's keep the second CT instance disabled for the moment.
 
In the Leveler, there's a mono check box.  When you check it (to sum the signal to mono), it goes silent.  Hmm...
 
Now, enable the second CT instance and check the left phase button (or right...it doesn't matter which).  Your signal comes back...the phase scope now shows a vertical line...and the "stereo" image is now in the center of your head instead wherever the out of phase thing put it.
 

Thanks for breaking it down for me, guys!
 
Plug-ins like Channel Tools are pretty interesting. Almost felt like I was in a Math class the way @reginaldStjohn broke it down. Lol I will go over it again slowly so, I can grasp your explanation. Nice work, man!
 
As for more info on the project... I used a stereo track which was exported in mono and stereo. Both came out silent. Had to go with 'Split Mono'. I know my iPhone plays in mono or joint stereo

I've never thought about using an iPhone to test mono-compatibility. 
 
Be interesting to see if you click the interleave on your master bus to mono you hear the same result.