Help me w/ Tempo changes via whole song without changing audio tracks' tempo

What you're describing doesn't happen in Sonar, at least not by default.

When you change the project Tempo, Sonar doesn't rebounce the audio clips to that tempo.

Sonar will change the Ruler and display in the Track View, but you should expect this... For instance, say you have an audio clip with a length of two measures in a project with a Tempo of 60. If you change the tempo to 120 for the project, the clip will remain the same, (play it and listen), but will now extend 4 measures instead of two, since the tempo is twice as fast.

Maybe you're confused by how Tempo works? In a Sonar project, there is no Project Tempo, there is only The Tempo. Each tempo setting in the Tempo View defines the tempo for Now Time. It's a little like driving at the speed limit. You see a speed limit sign, you look down at your display to see if you're driving at the current speed limit, call it 50mph. You see the next sign says 65 mph, so you speed up to 65. You drive a few miles until the next sign, which says 40 -- you slow down to 40. Sonar doesn't care what the speed (Tempo) "used to be", it only cares about the Now.

Measures and MIDI follow the tempo, not audio -- unless you rebounce the clip using an Fx (like Process / Fit To Time).

Well yes if you change the time signature, but I don't think you want to play in 4/8.

Think about my example above and you'll realize that if you want the audio to last the same amount of measures when you change the tempo, then you have to re-bounce the audio at the new tempo.

The simple facts are:

A 4-beat measure at 60 bpm is 4 seconds long, using a 4/4 time sig.

A 4-beat measure at 120 is twice as fast, so runs half as long, 2 seconds, when a quarter note gets one beat.

So what is it you really want to do?

I'm not sure if I understand you problem exactly, but what I think you are needing to do is change the time base of your audio clips to be "absolute time" as opposed to MBT or the MIDI. Select the audio clips in question and then in the clip properties change their "Time Base" to absolute time. After that, make your tempo changes and see if that gets you where you want.

Time Base
Choose one of the two options in this section to control what happens to a locked clip when you change the tempo:

Musical (M:B:T)--if the clip is set to the Musical time base, the clip's M:B:T position stays constant, and its Absolute position shifts.
Absolute--if the clip is set to the Absolute time base, its Absolute position stays constant, and its M:B:T position shifts.

I actually wish there was a global option to set this default to "Absolute" instead of "M:B:T". Most times this is what I have to do to avoid shifting audio clips when adjusting the tempo map after the fact.

I've been wondering the same question for ages now - how can I temporarily change the tempo of the song without screwing up the audio?

The reason I'd like to do this is so I can record some fast MIDI parts at a slower tempo. What I'd like to do is mute the audio tracks, change the tempo, record the MIDI part, then change back to normal tempo and have the song go back to normal.

However, whenever I've changed the tempo Sonar seems to make some drastic changes to the entire project (I seem to even recall instances of obvious audio-processing). I then get scared and immediately hit the undo button.

If all your audio starts at zero on the timeline no shift will happen. If you overdub a harmony part on the 3rd verse you wouldnt start recording at zero, maybe a measure before the third verse. If you then change the tempo, the overdubbed part will shift in relation to the original track you are overdubbing to unless you lock it. I wish Sonar had a default mode where audio clips would NEVER shift in relation to each other unless unlocked, not the other way around.

My google search brought me to this thread, which taught me something, but since I am using Sonar v.3, was not much help on how to resolve the same problem the others had. For example, I cannot select audio clips and force them to absolute time. I think this feature must have come after v.3

But I found a solution that will help these others:

I was deleting some audio out of an introduction (too long), and then selecting all the other audio to the right of the deleted space and shifting it LEFT to fill up the blank spot. Many of my audio clips were now out of place, just like the issue described above.

My Tempo events were a leftover from the MIDI tracks I had started with, and were now, kinda no longer needed. But to avoid the headache of moving dozens of audio clips by so many ticks, and experimenting with all the mess (again!), you just need to do the following.

SOLUTION: I went into Tempo View, clicked the button for Tempo List, and modified all the Tempo changes in the list to be exactly 6 measures less than they were before, to agree with the amount of audio space I had deleted and then shifted. This did the trick.

You realize you just responded to a thread started 5 years ago! 
 

I thought it was answered very clearly by kwgm.

We all work differently, The people who make Cakewalk ( or any DAW) cannot cover every possible scenario but they do a pretty good job of trying.
Some people only work with live recordings of real instruments. The tempo is set and it's a pain to change the tempo with audio. Your morphing the the waveform and this can only result in lowering the quality of your carefully engineered recording. You CAN change the tempo of an audio recording but this is not accomplished without some damage to the track. It might be insignificant damage, but myself I would only do this to lesser important tracks that are buried in a mix, I would never do this to my important audio tracks.
 
So I always start with midi and a few scratch audio parts until I am dead sure of the tempo. Then once this is for sure I start my serious audio recordings.
 
There are a few ways to change audio tempo that are well documented in the help files and tutorials so I won't even attempt them here. A few answers above touched on it.
 
 

i know its old but the answer was given by

Vovchik
Select all audio clips, press Alt+Enter. Switch "Time Base" to Absolute and check "Lock". After all your tempo changes uncheck "Lock".

 
Alt-Enter did nothing for me but looking at the clip properties inspector after selecting all audio clips, i changed the time-base to absolute and boom!, tempo changed, audio stayed put.