I'd like to halt or mute the metronome during a portion of a musical piece that departs from a regular, periodic tempo for a moment, allowing for some tempo-less musical meandering, and subsequently restart the metronome on the down beat of my choice.  The closest thing I can think of as an example is Little Feat's Willin', where the chorus is followed by "And if you give me...", which although bears its own sort of timing linking the vocal harmonies, is flexible enough tempo-wise to go almost anywhere until the down beat on "wine", at which time the tempo is back in its pre-meandering grove.
 
I can automate a mute on the metronome bus for the first such occasion in a song, but after that I can't think of a good solution.
 
I've been unable to find a way to just suspend the metronone until the downbeat on my say so, maybe with a footswitch to restart/unmute it.  I wouldn't care if Sonar wanted to keep counting steady measures quietly to itself and to just truncate the duration of that last measure before my downbeat, at which time the previous tempo would resume.
 
Any suggestions for how to do this?  Thanks!

right-click the mute button on the metronome bus and select "remote control". move your footpedal and click the learn button.  it won't start on the downbeat, but where you turn it on.  might help.

Another solution would be to not use the metronome - use a hi hat in Session Drummer - you can place the hits wherever you want

I just stumbled through a similar situation with an old Marshal Tucker song "Desert Sky" where at  the end there is all this slowed down part , then  a pause as they go " I like to watch the moon a --hiding". and those words are in a triplet time. But it was the same thing your talking about as the metronome was off to the "feel" of this one part of the song. 

I had to do two things . Draw a tempo map to slow it down through this part. 
And I made my own metronome track playing along using the rim shot and had only downbeats per measure through the transition. 
You could do the same thing. Make a midi click track and kill it in that part. 


Edit- I see Jonesey posted while I was typing the same idea, so it must be the best way for sure... :>

Thanks all.  You've given me some good ideas to try.
 
I could just go completely metronomeless and do a tempo map after recording a guide performance, but I like to have the intended beat occasionally rein me in to something steady-ish. 

bitSync


Thanks all.  You've given me some good ideas to try.
 
I could just go completely metronomeless and do a tempo map after recording a guide performance, but I like to have the intended beat occasionally rein me in to something steady-ish. 

Another thing you could do, is use a metronome bus (as provided on the most recent track templates) and then do a mute or gain automation on the bus where needed.

What if you: play to a given measure lets say 100 at 4/4 and 140 BPM.  Mute the metronome buss.  From measure 100 you ramble or stop.  At the point you start to play again, calculate the time and set some random tempo, (in the background and muted), that will result in having that point be measure 101.  At measure 101, you can have it set back the tempo you need.

"It works on paper"

+1 for volume automation in the metronome bus. Simples. 

but volume automation doesn't take into account that the non-linear, tempo-less groove can be of any length of time.  you can automate volume, but you have to know exactly how long the improvisation is going to be, which is in most circumstances, unpredictable.

bitSync


I'd like to halt or mute the metronome during a portion of a musical piece that departs from a regular, periodic tempo for a moment, allowing for some tempo-less musical meandering, and subsequently restart the metronome on the down beat of my choice. 
...
 
I've been unable to find a way to just suspend the metronone until the downbeat on my say so, maybe with a footswitch to restart/unmute it. 

I missed the reference to the footswitch that implies you want to do this in live performance.  That is to say...you intend to do your "meandering" live, and then pick up the sequence with some sort of performance gesture.
 
You might want to break the song into two different projects, and then play them back to back(ish) via a playlist.  The first project comes up to the "meander" part and ends.  (Insert you personal live meandering here.)  Then the next half of the song is queued up in the playlist to be started when you hit the spacebar or whatever.
 
Does that sound more like what you're looking for?