Am I imagining it? Sometimes, it seems slower than it played before. I have not mastered the song, just checking the mix.

 

Spoiler: ChtaGPT KI

You're probably not imagining it, but the exported file itself is usually not changing tempo. More often, one of these things is happening:

• Your perception changes between listens. After hearing a song repeatedly, your brain starts focusing on different elements. A dense mix can feel faster; a sparse mix can feel slower.
• Mastering/limiting affects perceived energy. Even if you haven't mastered it, changes in compression, EQ, or loudness can alter the sense of momentum and make a track feel faster or slower without changing BPM.
• Different playback systems. Bluetooth speakers, phones, streaming services, and DAWs can have slightly different buffering or playback behavior. The tempo is generally unchanged, but the groove may feel different.
• Sample-rate mismatches. This is one of the few technical issues that can genuinely change speed and pitch. For example, exporting at 44.1 kHz and playing back incorrectly as 48 kHz (or vice versa) will make the song play faster or slower and change pitch.
• Tempo automation or warping. If your DAW has tempo automation, time-stretching, warping, or elastic audio enabled somewhere, an export could differ from what you expected.
• Listening fatigue. After working on a mix for hours, perception of timing, groove, and energy can become less reliable.

A simple test:

1. Import the exported file back into your DAW.
2. Align it with the original project at bar 1.
3. Zoom to the end of the song.
4. Check whether it stays perfectly synchronized with the project.

If it drifts over time, there is likely a sample-rate, clock, or time-stretching issue. If it remains aligned, the tempo is identical and you're hearing a difference in perception, mix balance, or playback.

What DAW are you using (Logic, Ableton, Cubase, Reaper, etc.)? The likely causes vary quite a bit between DAWs.

 

Ignore the AI stuff. Check in the export page (or settings, since you didn't say which DAW) if you have the option of writing tempo to WAV enabled. Some players will respect the written tempo, so if it's not accurate to the song, it will sound different than running it inside the DAW. I had a similar issue with Studio One back in the day.

Edit: in cases where it didn't come from you (like mixing and mastering someone's else music), you usually can right click the track in the DAW and it will show the track tempo embedded in. You can usually just delete that tempo and the file will go back to what it was supposed to be.