Hi John. Expand the size of the audio track in the trimmer by positioning your cursor on the border between the audio track and the video, then click/dragging it up and see if that fixes it. When the audio track is too small in the trimmer, zooming doesn’t work on it.
What about the arrow keyboard keys – did they work? Also what version of Vegas Pro are you using? I Tried what Tim suggested and found that I was not able to change the height of the audio track independently from the video (in the trimmer). By grabbing the top of the video track I could reduce the size of both tracks. If I made them as short as possible, then the mouse wheel did not zoom the tracks. I did find that you had to click in the trimmer track to permit the mouse wheel zooming. if you clicked anywhere else in the trimmer window (e.g. on the video pane or on either side of the video window the mouse wheel would not zoom the track.
?? You aren’t able to increase the size of the audio track in your trimmer? Move your mouse cursor to the top of the audio track in the trimmer (between the trimmer audio and trimmer video) until it turns into an up/down arrow icon, click, then drag up.