Audacity desynchronizes with my recording over time

I’m using a Shure SM 58 with an XLR to USB cable, plugged directly into my computer. I’ve used it for audio conversations on Skype with no issue. When I record just using the mic and nothing else it seems to work just fine, but then again I have nothing to compare it to. The problems begin when I take a fresh render of a song from FL studio, import it as a WAV, and then try to record accompanying tracks. The recording starts off in synch with the song, sounds great, no issues. But a few seconds in, things start to come off synch. By the end of the song, it’s not synchronized at all. From what I can tell, the audio I’m recording is ending about 1 second earlier than it should, which means either the playback is fast, or the recording is. I poked around and learned that this might have something to do with Sample Rate? But nothing I found actually described how to SOLVE the issue, it merely described it.

It probably is a “sample rate” issue. The “cable” isn’t just a cable, it’s an audio interface or half a “soundcard” and it might be built-into the USB connector. The “cable” has a sample rate clock, and your soundcard has a sample rate clock and they will never match perfectly.

Good Audio Interfaces are usually better than consumer soundcards or “adapter cables”. Plus, you can use the same interface for recording, playback, and monitoring.

…If you buy an interface you might want to look for one with zero-latency direct-hardware monitoring, where the monitoring path doesn’t go through the computer. (You can still play the backing-track through the interface.)

Pros use super-accurate expensive master clocks (often atomic clocks) and interfaces with master-clock inputs.

Since pitch and tempo are tied-together by the sample rate, musicians usually notice pitch problems before they notice tempo problems, especially over the duration of a song where a few accumulated milliseconds aren’t too bad. That makes a frustrating problem because you can sing (or play) in-tune with the backing track but when you mix (or play back) you voice is pitch shifted and you are out-of-tune.

But there is another possibility - Dropouts… Missing bits of data caused by interrupts make a shorter-faster file when you play-back without the tiny gaps. (usually this also creates an upward pitch-shift). But in that case you usually hear little clicks & pops where the audio is discontinuous.

Could you please recommend a solution rather than just describing the problem? Thank you.

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