Hmmm ... that's odd. That's the way I do it.
I really debated whether to actually post what's below, because I fear I may make things less understandable for you. But here it goes:
I don't know which version you have, but I'm using Melodyne 4 Studio. I just tried it my usual way to make sure I'm not insane and it worked. I loaded a wav file into an audio track, dragged it up to the timeline, and saw the effects of the tempo detection.
Then to modify the tempo map, I created a region FX for the clip using Melodyne. When the Melodyne window pops up in the MultiDock, I switch to Melodyne's Note Assignment mode, Show Tempo Map, and dragged one measure line in the tempo map in Melodyne way to the right, thereby decreasing the tempo. Note that more notes (blobs) will fall now within that dragged, expanded measure. Went back to Melodyne Edit mode (not sure if this is necessary), dragged the Clip back up to the timeline, and now the clip displays in the clip pane with the measure I drew out further looking "contracted", and the overall length of the clip decreasing by a measure or two.
How do you know it didn't work for you? Did you check Sonar's tempo map and listing under Views? Also be aware that the tempo mapping will not alter the speed of audio clip playback (the audio clip will sound the same as the original). One way of thinking about it is that Melodyne's Tempo Mapping allows you to slide the beat and measure lines around with the audio being the constant reference. Depending on your adjustments, some beats/measures will be longer than others, and Melodyne will compensate tempo to make it so ... and thus the resulting audio remains the same. In Melodyne, the result is manifested in the tempo map expanding and contracting. Since Sonar uses an evenly spaced Time Ruler, the result is the playback line will speed up and slow down according to the tempo map (turn on the metronome for playback!), since the audio waveform has contracted/expanded but is still displayed on a linear time grid (MBT).
I hope I haven't done more harm than good in attempting to explain this. It can be very confusing to explain. It's better experienced by doing.
I don't recall exactly how I finally figured out the tempo mapping in Melodyne, but I'm pretty sure it was a YouTube video, but not from Melodyne. The videos from individuals I found are often more helpful than the Melodyne produced videos. I also found that it's important to understand the tools corresponding to cursor placement within the various locations in the Melodyne tempo plot. It's not always straightforward.
Hopefully this helped in some respect without making matters worse.
Gulp ....
Press Submit ....