Export audio advice needed ... sorry!

Can someone clarify export audio issues for me?  Everything is out through the master bass (I mute the master buss to check). I export the audio. (I've tried 'what you hear', select all including the busses, bounce to track and many other permutations) but when I do a null test, I don't get silence. (I export the audio back in, send straight to soundcard (not through the master buss), flip the phase) When I do this I hear a reverberant version of the song (quite loud), sometimes with short 'chattery' sounds too.
 
I tend to think it's something to do with reverb.
 
Can I ask? Does spin and wander on the likes of Lexicon reverbs cause this kind of anomaly? i.e. that the reverb is never the same when the project is replayed? So if the mixed is bounced down and imported for a null test, silence doesn't happen because the reverb behaves differently with each play of the original mix? So when you play the phase inverted bounced track together with the mix, they are not the same?
 
I read that freezing tracks could avoid some export audio problems, but I don't know how that can help in this case where the reverb is on a buss as a send effect.  In a typical project with a vocal for example, I have eq and compression on the vocal track, I send that to a vocal buss and insert a send to a reverb buss. I can freeze the vocal track (with the eq and compression), but If other tracks or busses are sent to that reverb buss, all I can freeze is the original track itself? So I've tried freezing, but still don't have any success and still don't have anything like silence with the null test.
 
The other thing I'm wondering about is the mono/stereo/interleave thing and if that's something to do with it:
 
Let's say I have one mono vocal track. On that track I have eq and compression. I want to send that track to a buss (I may want to use the buss to do further volume changes with an envelope for example or send to another buss for parallel compression or have a send level envelope or the likes) I also want to send that vocal buss to a reverb buss (along with other tracks)
Should I therefore have the interleave button on the original mono vocal track set to 'stereo' since I'm sending the original mono vocal track to a stereo buss?  (I'm asking this as when I do the null test it seems as if the resulting reverby sound from the vocal in the null test  is pulling off to one side sometimes)
 
I think the 'chattery' sound is something to do with Slate Digital Virtual Tape Machine plug in, but to be honest, I'm fed up trying various things to get the null test to work, that I'm just hoping someone on the forum can help)
 
The resulting difference doing the null test is significant. It's nowhere near silent and sounds very 'middly' and I think!? the exported audio sound duller and muddy in the low mids. (i should have checked if there were any volume differences between the original and exported audio before I wrote this and have now turned off my computer, but from what I can recall from other experiments, I think there are.) I'll check that again, but was just wondering for the moment if anyone else is in the same boat?
 
For reverb I'm mostly using Lexicon PCM Native Reverb and Altiverb.
 
Many thanks

Hi Johnny V
 
Thanks for the reply.
 
I've tried all sorts of export settings and removed plug ins over time. It's the reverb plugins I'm having the difficulty with I reckon.
So I suppose it's whether random elements of a plug in like Lexicon PCM affect the null test in a dramatic way and cause the null test to fail. The null test sounds like full on reverb, it's not just a faint sound. That's why I'm also wondering about the mono/stereo interleave thingy in relation to reverb settings.
 
I usually just choose the default setting for exporting. All the tracks selected and 'entire mix'. I should double check the 'what you hear' option (which I recall being there) although I'm pretty sure my drivers are set to ASIO.
 
I also notice yesterday that when I muted the master buss and there was no sound therefore, that it still looked as if there were what looked (in the waveform preview) like random little spikes in the graphics (which I thought might be something to do with the 'chattering' issue even though I couldn't hear anything.)

Hi John T
 
Yes, I record/mix in 24bit 44100hz and export as same and export to WAV.

Any processing that involves any random elements is not going to null if you export the audio then reverse phase the exported audio and play it against a fresh playthrough of the original mix.

An exported wav file should null against a phase-reversed copy of itself, but that is a different thing to what you seem to be doing.

Many plugins can contain random processing - reverbs quite possibly, maybe the Pro Channel console emulator (don't know for certain, but unless the switch that adds in the algorithm which introduces some randomness to tolerances never recalculates then it will), some modulators and, obviously dithering can as well. Any plugins using random noise as an audio source (e.g. synths, tape emulation, maybe guitar effects) will be different. Maybe some plugins that emulate analogue circuits might vary a little with each run through - certainly the original analogue circuits would so I hope the emulations would as well.

Then having removed all those possibilities for non-nulling you have to perfectly match the level of the nulled copy with the level of the rest of the mix and place it with perfect sample accuracy.

To be honest I'd be surprised if a phase-reversed copy of an exported mix would null with the non-exported mix. It might, if everything is done perfectly, but once any variables at all are introduced then it won't.

Why is this even an issue?

TLW's question is a sensible one, I think. Do you have any reason to care about this? Does the exported mix sound good to your ears? Does it sound strikingly different to what you hear when you play the song in Sonar?
 

Thanks for the answers to my query. I just wanted to clarify that reverb etc. variations on playback would not null. One of those moments when you think you've being doing something basically wrong in the routing and exporting of projects , like for years!