Mono and Reverse Polarity Explanation
"According to your manual and blog on the subject, if I switch the
polarity of left channel, and then press mono, I should hear only the side
of a mid-side mix, which is great for checking reverbs, width of mix etc.
However, I can only hear this in mono, which doesn't help much! Is there
anyway to hear the side of a side/mid mix in stereo, using the id22
hardware controls? (I know its possible to do it with plugins like Ozone,
but it would be great to be able to do it to anything going through the
id22, so I can check playback from any app on the fly)"
What you are asking for here is a mid/side matrix (full stereo) with a mid mute or side solo function. This is actually different to how the majority of monitor controllers work when it comes to L-R and L+R monitoring.
On iD22, you invert the left channel (-L) and sum it to the right channel (R). This makes a L-R, and provides that output (you can call is S if you like) to both speakers. This will highlight any stereo material such as reverbs & delays etc - but they will be presented in mono or from both speakers equally.
If you want to listen in mid/side - you need three channels so that you can spread the L-R difference across the stereo field. I'm afraid that if you want to listen like this (it normally makes my head turn inside out!), you'll have to do this with Ozone, a plugin or a collection of channels in your DAW.
Using iD22 and any monitor controller that offers this -R feature to combine with L in mono - you need to listen for what remains (as in what is not cancelled out) and what is lost. Comparing that to standard stereo or indeed mono (listen for what cancels here) you can find out if you have too much anti-phase stereo information.
For example - if something cancels out in mono - then it exists in the stereo field with some anti-phase - reverb tails, double tracks panned, intentional widening tricks etc. If you lose bass in mono, then you might want to address the phase cancellation in the left and right bass channels for example.
On the flip side, listening with polarity reverse and mono sum on will show you what has been lost in mono and is like the polar opposite image of mono (yes still in mono) but the information is what's useful. Anything common to both L and R, say centre panned kick, snare, vocal etc will be cancelled out, leaving the stuff that exists differentially in the left and right channels.
I think if you get used to looking for issues in this way - you'll find iD22 pretty for on the fly checking. However if you do want to actually listen to the stereo side signal (like in an M/S pair) then you will need to do this in the DAW as iD22 does not have a way of doing the full M/S matrix with mutes/solos easily.
I hope that helps. Personally I used to have the Voxengo MSED plugin (AU or VST) in my DAW for muting either the mid/side signal - so unless you use Pro Tools, that is a free plugin that will do what you require if that helps! www.voxengo.com