GZIP Compression is not authorized

Hi,

Our site does not load very fast even though there is not much content. I used WP Smush to compress the images, and I had a low score with Hummingbird for "Enable Compression". The score was 50%. Will enabling compression have a very large effect on the load times? If so, it would be worth it to do the GZIP compression. Unfortunately, GZIP compression is not authorized, do I have to add some code myself? I don't think it's a plugin that's blocking it. Here are all my activated plugins below (I don't have any inactive plugins):

Elegant Themes Updater
Ultimate Branding
Wordpress Importer
WP Hummingbird
WP Smush Pro
WPMU Dev Dashboard

Thanks in advance for your time,

Kristy