Compression slider in audio import settings doesn't seem to affect anything.

According to the manual, compresion slider on import settings supposed to tweak amount of comopression to be applided to a a compressed audio clip, for which I expect audio clip's file size or sound quality to be changed.

But when I played with my ogg bgm audio clip, changeing compression slider back and forth doesn't seem to affect anything on my audio clip.

Well, it does show the new file size on inspector, but when I exported them in to assetbundles, its file size doesn't seem to be changed at all.

I fear that what I've complained so far could be seen very stupid, but please kindly explain me what compression slider on audio clip import settings exactly do.

Thanks in advance.