What effect is this?

[Mentat]

A volume swell/softened attack effect on the guitar...
-Rush- La Via Strangiatto (Alex Lifeson's solo)
-Opeth- Black Rose Immortal (brief guitar interlude almost right in the middle of the song.)
-Eucharist- Floating (early in the song after the intro)
-Steve Vai- Erotic Nightmares- around 3:12.

There's more I can't recall right now.

I'm thinking it's an envelope filter. Or is the extent of an envelope filter's capabilities lie in creating a wah effect? Because I can't picture someone frantically stepping on a volume pedal to soften the attack of each note on the examples cited.

 

[guitarist]

On La Vila Strangiato the lengths of the swells aren't always the same so I imagine he's just using the volume knob on the guitar (I've seen Yngwie do that) or using a volume pedal. It seems like it would be easier with the pedal though.

 

[Agtronic]

I just listened to the Vai track ... I knew it was going to be that when guitarist wrote "volume knob" ...

Ditto for the vai song, but he was probably using a volume pedal to get that effect, leaves your hands free.

 

[grinder]

Check out Cathedral by Van Halen.I read Eddie had to keep changing the volume pot on his guitar while recording, because it kept overheating and locking up.