i know it should make no difference but comparing using replaygain and then turning it off, when off the music seems less compressed and more dynamic.
is this real or just my imagination
i am using fiio x7/foobar/mojo (coax) and hd25 aluminiuim (modded)
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On average the sound will be a good deal louder without replaygain, and loudness differences can cause soooooo many subjective impressions beside feelings of loudness. It's the very reason why we tend to dismiss or look very skeptically at any feedback not involving matched level outputs.
Replay gain in itself does not compress anything. The basic stuff is just an extra metadata(so the track is still the same) telling the player to digitally reduce(or increase) the amplitude by XdB on playback.
If you apply it to very dynamic tracks like most classical music, then you need to pay extra attention or the result will often be a boost and the track could clip. In foobar you just have to pick the replaygain setting with prevent clipping in it and so long as the replay gain scan was done with some amount of oversampling(to catch intersample peaks), you should be fine. If not, maybe you're getting clipping or compression because some other DSP is handling the clipping(some form of compressor could do that, but you have to put it there?).
In any case, it's easy to check if the song you find "compressed" has a positive or negative replaygain value after being scanned. Right click on the track pick properties, and go to the second tab called "details" in the pop up window. If replaygain lowers the volume, then I don't see how it's going to compress anything. It just sound quieter and your brain makes up a story about how that feels but it's probably just quieter.
I don't remember if you can show gain and peaks just with a right click on the columns line by default, but it's foobar so you can always add stuff:
I have this pattern showing track gain %replaygain_track_gain%
And this one showing what the replay gain scan saw as track peak %replaygain_track_peak_db%
those can be added in "preference"->"display"->"playlist View". And just "add new" in the custom column if you're slightly paranoid like I am ^_^.
Just note that the peak value is that being scanned by the replay gain tool, it isn't necessarily the true peak value. You can select the amount of oversampling and even the type of resampler in the gain settings and the resulting peak value displayed will change based on those settings. The higher the amount of resampling, the more accurate the value. But at the same time you radically increase the CPU usage while scanning for replaygain, and increase the duration of the scan. so, many people will just chose a lighter scan option and don't worry about potential small clips(most actually occure at low freqs and aren't perceived as clipping). Or they just remove 2dB or 3dB on the preamp ("preferences"->"playback") to deal with the possible error in the true peak reading and just stop thinking about that.
I'm guessing I went well beyond your specific situation, but we never know what you are actually experiencing. And that might still interest someone using foobar.
edit , I don't know how the X7 handles replaygain, but I'm guessing it's still based on foobar's metadata.