How can I get Apache gzip compression to work?

I can't get my site to use gzip compression.

I recently watched this video by Chris Coyier over at css-tricks.com. In the video, he talks about enabling gzip compression to make websites run faster.

As per his instruction, I linked through to github via html5boilerplate.com, copied the gzip compression code from their .htaccess file, pasted it into my own, and uploaded it to my site.

I've tested it via gzipwtf.com and it doesn't seem to work. Can anyone help me with this?

My .htaccess file looks like this:

# ----------------------------------------------------------------------
# Trim www
# ----------------------------------------------------------------------

RewriteEngine On
RewriteCond %{HTTP_HOST} !^orbitprint.com$ [NC]
RewriteRule ^(.*)$ http://orbitprint.com/$1 [L,R=301]

# ----------------------------------------------------------------------
# Gzip compression
# ----------------------------------------------------------------------

<IfModule mod_deflate.c>

  # Force deflate for mangled headers developer.yahoo.com/blogs/ydn/posts/2010/12/pushing-beyond-gzipping/
  <IfModule mod_setenvif.c>
    <IfModule mod_headers.c>
      SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding
      RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding
    </IfModule>
  </IfModule>

  # Compress all output labeled with one of the following MIME-types
  <IfModule mod_filter.c>
    AddOutputFilterByType DEFLATE application/atom+xml \
                                  application/javascript \
                                  application/json \
                                  application/rss+xml \
                                  application/vnd.ms-fontobject \
                                  application/x-font-ttf \
                                  application/xhtml+xml \
                                  application/xml \
                                  font/opentype \
                                  image/svg+xml \
                                  image/x-icon \
                                  text/css \
                                  text/html \
                                  text/plain \
                                  text/x-component \
                                  text/xml
  </IfModule>

</IfModule>

Try this :

####################
# GZIP COMPRESSION #
####################
SetOutputFilter DEFLATE
AddOutputFilterByType DEFLATE text/html text/css text/plain text/xml application/x-javascript application/x-httpd-php
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html
SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip