The volume of the sample decreases when you import it.

[random user]

Hi. Over time I import a sample, its volume decreases. Can anyone do a lot of explanation on why this happens?

[Exhale]

OMPT has its own internal volumes for samples and 'synths' (vsts and opls) as is shown in the first attached screenshot. As you can also see in the attached 1stSS those volumes are initially automatically set to the default 48.
Sometimes if you import soundfonts they will also have their own default volumes from the file, the reason I mention this is because they also import as sampled instruments with instrument properties already in the mix (see screenshot 2).
I suggest you mess with these and see if that helps your reference.
The reason they sound different in volumes before the preview and after, if I am correct, is the preview playback system is a different one to the one within the track you are working on.
I hope that clarifies things.

(Please correct me if my explanation is wrong more technical guys, but I think this is a decent answer to this, at least in layman's terms.)

[Saga Musix]

As Exhale says, there are many volume factors across the OpenMPT, maybe even confusingly many! You can hover all volume UI elements to see their volume reduction in decibel (e.g. -6dB = half volume):

- Global Volume: By default at 0dB, so no reduction in volume.
- Sample volume: The exact volume here depends on the module format and mix mode, for MPTM the defaultr sample volume is -8.52dB, for IT/XM it's -14.54dB.
- All sample-specific volumes are at 0dB by default, unless the sample or instrument thta you import contains its own volume settings.

Why does this happen? Well, a signal playing at 0dB is already the loudest you can have without clipping. So if every sample was playing at 0dB by default, your signal would already clip when playing just two samples at the same time. So by default, samples are played at a lower volume, so that you can play more samples simultaneously without clipping.