whats an expander for

[effectsnut]

logic tells me it expands the mix. but then ive heard of downward expantion..how can i use an expander. is there two ways?
also should you use a compressor and expander at the same time?

thanks

[Stealthtech]

Used for widening your stereo image, allowing you to create an ambient, spacious mix that extends beyond the normal stereo extremities. Also acts as a compressor itself.

[mixsit]

http://homerecording.com/bbs/showthr...d+AND+expander