Many might know this trick if you do well gratz if you don't enjoy.

The remain button is my most underused button on my sp404sx, but the other day I found a use for it that will give a lot more of a reason to use it. I found out if you hold the remain button down and and press mfx or another effect it will apply that effect to all the pads. So that seemed awesome and all but still not that great...

Then I found out that you could actually select individual pads while holding down the remain button, and choose which pads will have the effect (mfx,isolater,etc.) applied.

Then I realized if I use the equalizer (mfx) effect to mute the sample completely I can now use the remain button to apply the muted effect to samples while they are playing.

This is great for pattern select mode so you can have a whole song in one pattern pad and just mute what parts of the song that are no longer needed or you can unmute parts that would be coming up. It is also good for resampling but can be a little trickier because if you don't have the mfx or effect applied to at least one pad it will shut down the effect hence the pads you remain select will not have the effect applied. It is still easily doable just takes a sec to figure out. Use a dummy pad or remain select mfx to apply it to all pads and turn off which pads you want to play.

By the way this is in the manual its just hidden and under implied.

yup, and using the subsonic you can also bring stuff in from quiet to full (or vice versa) using the same trick.