Thanks for all the help, folks.
I actually found a Nyquist plugin called Time Shifter that does what I want. Well, at least is makes it easier.
Problem is, I tried it on a couple of files, and found the result not to be quite right. I can’t put my finger on it, but it’s like the soundstage is still diffuse.
So I tried shifting the time manually via the drag method. Same result. The plugin works as expected, meaning I can see that the signal has been shifted by 1.5 ms, but I don’t get the clear center image I’m expecting.
My baseline approach was using Garageband. This is more tedious, which is why I turned to Audacity. However, the Garageband result sounds fantastic while the Audacity result does not. I have no idea why this is but I’m trying to figure it out.
I am using the same input file - an MP3 file, which I realize is far from ideal but this is just for experimentation purposes. (Once I get this all figured out delay-wise I will obtain uncompressed files for the source)
In Garageband, I use their built-in MP3 export.
In Audacity, I installed the LAME plugin to allow MP3 export.
In Garageband, the process of adding the 1.5ms delay is more tedious because Garageband does not allow you to manipulate only the left or right independently; so one must import the file, copy it to a second track, mute the left channel of one track and the right channel of the other track, drag the one track to the right by 1.5 ms, then export. The result is a very focused center image and very good staging.
In Audacity, I simply import, go to my Time Shifter plugin, type in my 1.5 ms delay, then export. The result should be the same, but the Audacity version has a very poor center image, and the staging is muddy and diffuse.
Not sure what else to try.