Mixing: What is the 'Pedalboard Exception'?

Should you send your mix engineer raw WAVs or crafted and polished stems? Your answer to this question will make your mix engineer either love you or hate you.
The Pedalboard Exception: A metaphor for a sound created by a producer that should not be altered by the mix engineer in any way.
Firstly, what do I mean by raw WAV in this context?
I mean one track of your multitrack recording bounced to a WAV file without any insert or bus processing or effects. So imagine during your recording process you had applied EQ, compression and reverb to the lead vocal, to give it a context for the other instruments and background vocals. For your raw WAV you would disable your insert plug-ins and mute the reverb track.
The reason you would do this is that you want to give your mix engineer as much flexibility as possible. There's an expression 'Why keep a dog and bark yourself?'
Following this reasoning, then no matter what processing and effects you have applied in your DAW session, you should switch them all off before printing WAVs to send to your mix engineer.
Congratulations, you've done it right and your mix engineer loves you! You have used insert and bus processes and effects to give you context during the recording process. But you realize that although you are the master of your own musical expression, the mix engineer is massively more experienced and skilled in gelling sounds together to make a great record.
But there is an exception...
The Pedalboard Exception
If there's a good reason why you should disable your inserts and bus processes and effects before exporting WAVs, then you might also consider why this would not apply to your guitarist's pedalboard effects.
Well yes, there's the very good reason that you've already recorded them and you can't switch them off. But the question is more a case of "Why would you not want to?"
The answer is that the pedalboard is part of the guitarist's sound, as is their amplifier and loudspeaker cabinet, or their own personal amp emulator. Other than technique, guitarists spend all their time working on their tone. TONE is a big word among guitarists, and rightly so.
So the sound that comes out of their loudspeaker cabinet, or their personal amp emulator, is their sound. And as a recording or mix engineer you would absolutely not want to deny them that.
So is this the Pedalboard Exception? Not quite...
If a guitarist strives to develop their own individual and unique tone, then perhaps as a producer so should you.
So you might for instance develop your own signature vocal sound - I'm going to say 'sound' from now on because 'tone' is a word that I feel should belong to guitarists rather than engineers and producers.
So your signature vocal sound might require a particular mic, a certain shape to the EQ, a particular compressor and ratio, a John Lennon-style delay, and perhaps a reverb preset that you have carefully crafted yourself, the parameters of which you keep tightly under lock and key.
Are you going to switch all of this off to send to your mix engineer? No way. NO WAY!
This is an example of the Pedalboard Exception. It's a metaphor for a sound that is exactly as you want it to be, and you don't want the mix engineer to alter it in any way.
Under the terms of the Pedalboard Exception you would not export a raw WAV of the track; you would export a stem.
What's a stem?
Trying to keep this brief - From the film industry: dialogue, sound effects, music. They are the three principal stems. All of the dialogue is mixed into one stem; all of the sound effects are mixed into another stem; all of the music is mixed into a third stem. Then the stems themselves can be mixed. It's a time-tested working procedure. There's more info here...
In music recording, stems are generally groups of instruments or vocals that can be balanced easily among themselves, like a drum set, or background vocals, or anything else that works nicely as a little sub-band in the mix.
So if you're mixing yourself, you could premix the drums, premix the background vocals, and perhaps premix rhythm acoustic and electric guitars. Then you can deactivate the original tracks and have a very much simpler mix screen to work with. It can make a lot of sense.
So you might think of doing this to send your song to your mix engineer. Send him or her stems of the drums etc. and individual tracks of everything else. (You're limiting the range of options that the mix engineer has, and hopefully you realize this and have a good reason for doing it.)
Or you can take this to its (il)logical conclusion and regard each track as a stem. So you export each track individually with all of its insert and bus effects and processes intact. This is why your mix engineer hates you. Their flexibility is now reduced to faders and pans, and possibly applying yet more effects.
Invoking the Pedalboard Exception
In view of the above, we can see that it would not be productive to export each individual track as a stem with processes and effects. But if you go to the other extreme and export all of your tracks as raw WAVs you can't show off your signature sounds.
So the solution is to think about that guitarist's pedalboard. If the sound you have achieved on any particular vocal or instrumental track is as significant as the guitarist's tone, then you need to export that track as a stem with processes and effects.
You have invoked the Pedalboard Exception.
But at the same time...
Give the mix engineer some wriggle room
It doesn't have to be either/or. If you really desperately want to export a track as a stem, but you're worried that the mix engineer won't like you cramping their creative style, you can export both.
Yes both - export that track both as a raw WAV and as a stem.
And since you will be giving your mix engineer some notes (and possibly your own rough mix), such as what's important and what's not, what kind of dynamics you want to hear etc., you can very clearly state that the raw WAV and the stem are alternatives. Your mix engineer may realize this almost instinctively, but they'll have to compare the two tracks all the way through to be sure. You can save them important time and brain compute cycles just by telling them what's what.
In summary
You'll win friends and influence mix engineers if you send them raw WAVs to mix. Sending too many tracks as stems-only hampers their creativity, which is what you're paying them for.
But if you have developed your own sound for a particular track, or couple of tracks, then export stems of those tracks as well as the raw WAVs. The mix engineer can either use your stems, or work with the raw WAVs and improve on them as they please.
The Pedalboard Exception - It's the best of both worlds!
Photo credit: Kit Rae.