You're going to have to compromise the attack of the sound to some degree, because if it's happening at the onset of every note then it's a part of the transient of the sound.
If it's a pad, though, why do you want it to have a sharp attack? Traditionally speaking, a "pad" is an extra background element used to fill out space in a song, and generally you want transients on things that you want to call attention to. Not saying you're not allowed to have a pad with a fast attack of course, but it's a question worth asking.
Edit: Also this is technically a sound design question, so I'm gonna move this over to that section.
