Your microphone has electronics inside. That’s how it works. It’s not simple and passive like a rock band microphone. Some electronics can be powered with an internal battery (many shotgun microphones do that) and some don’t use an internal battery but depend on the mixer or device to supply battery voltage up the cable. That’s what P48 Phantom Power is. I have a good quality microphone that uses P48.
M-Audio M-Track two channel mixer
Actually, you bought a two channel audio digital interface. It’s not a mixer. Anything you plug into the left of the device is going to appear on the left of a stereo show. Plug into the right and the sound will appear on the right.
If you look at the Audacity red recording meters you only have the top one, correct, not both, and you only have one set of blue waves on the timeline? Audacity will tell you what’s going on if you know how to read the graphics.
The fastest way around this is to make your one music track into Mono.
Use the black arrow drop-down to the left of the blue waves and Split Stereo Track to Mono. Then delete the dead track. That should play to both sides of your headphones and speakers.
If the device headphone connection lets you hear your Audacity playback, then it should let you produce sound-on-sound overdubs with no delays, latency or echos, but I wonder about the channel problems on the second pass. After you lay down the rhythm track and split to mono, the new, live vocal track (or whatever you want to do next) is going to record Left-Only Stereo again… That’s going to sound funny in your headphones.
You can force that to work, but it would make me crazy.
I don’t think this is going to work, but look at the device toolbar just above the blue waves and see if you can make a recording with the input set to 1(Mono) instead of 2(Stereo). I half-way expect that to fail, so you may need to put it back.
There may be something you can do in Windows, but I’m not a Windows elf.
The other obvious way out is get a “Y” cable and plug your microphone into both left and right. I would not recommend that. It could mess up the noise level of the microphone and you could have Phantom Power P48 problems.
Overdubbing does have to be adjusted. Audacity doesn’t really “know” how to overlay your fresh track with your old one. You have to guide it.
We published three hardware examples of how to overdub with no latency or echoes, but the three examples are either full stereo already or natively mono, so they don’t have the mono/stereo cross problem you do.