I just found out how to do this, so I'll document it here for future reference.

There are two methods for converting stereo to mono:

1. Split track method - Select Split Stereo to Mono from the Audio Track Drop-down menu. That's the downward pointing arrow right next to the name of the audio track to the left of the display to the audio track itself. You can use this method if there's little variation between the two channels.
2. Mix track method - If there's variation between the two channels that you want to preserve, use the mix track method. Select both channels by pressing CTRL+A. Select Mix > Mix Stereo Down to Mono from the Tracks menu at the top of the screen.

For anyone who doesn't already know, here's the settings to save for Oblivion.

 

Export to MP3, and under Options select constant bitrate, 64kbs, joint stereo

On 1/22/2023 at 5:23 AM, Vorians said:

For anyone who doesn't already know, here's the settings to save for Oblivion.

 

Export to MP3, and under Options select constant bitrate, 64kbs, joint stereo

Are those for voice files?

It depends on what the sound is for. For ambient sounds, it just needs to be a mono WAV file.

For voice files, yes. After converting to mono as per your opening post, those are the export settings to use or the files won't play in-game. I'm certain that ambient sounds require constant bitrate and 64kbs too (if you're quering because of the "joint stereo" part, don't worry, that's just what Audacity needs to be set to, the result will still be mono since you've made it mono during editing).

I don't know what constant bit rate is but the bit rate can be pretty much whatever you like. I've seen as low as 64 kbps all the way up to 1411 kbps. They are WAV files, not MP3. Heh, I just found one that isn't even mono. It's the initialization sound for Oblivion XP. I guess that's why it's 1411 kbps.