Anyone know if resampling a 44100 file to 48000 can improve sound quality or is it like trying to increase the resolution of a low-res image, just makes it worse? Thanks.
No, Yes 
Upsampling won’t add anything in terms of quality. It adds a very small risk of artefacts. So quality will never be better and sometimes a very little bit worse.
You might need to upsample sometimes, fi when supplying audio for video. And some rare plugin might work/sound better at some sampling rate. But that’s more a case of sloppy programming than it’s a case of “better”.
Okay, thanks. I’ve worked with image files a lot more than audio and I wasn’t sure if I’d be wasting my time, so I thought I’d ask. I recently got my hands on some high definition audio files that I resampled to 48000 and they sound amazing. I was hoping I might be able get the same quality by upsampling some of my old files, but probably not. 
I recently got my hands on some high definition audio files that I resampled to 48000 and they sound amazing.
Those recordings would probably sound amazing at 44.1kHz too… They’d probably sound amazing as high-quality MP3! It’s usually the quality of the recording & production rather than the quality of the format. Sometimes they take more care, or they use less dynamic compression with high resolution files.
The guys at HydrogenAudio who’ve done scientific, blind, level-matched [u]ABX Listening Tests[/u] have pretty-well demonstrated that “CD quality” (16-bit, 44.1kHz) is better than human hearing… If you take a high resolution recording and downsample to 16/44.1, you can’t hear a difference between the high resolution original and the downsampled copy.
We’ve all heard low-quality MP3s, it’s often difficult (or impossible) the hear the difference between a high resolution original and a good quality (high bitrate) MP3 (in a proper blind listening test).