Hi there! We have a few ways that you can see the rates of audience joins:
Audience Visits Metric
When an audience is clicked on, a visual graph is displayed with the number of joins for the given time period. Time periods of "Rolling Day", "Rolling Week", "Rolling Month", "60 Day", and "90 Day" are available. Data points are broken out by day where actual numbers are displayed if you hover over the dot for each day.
In the AudienceStream Dashboard, there is a widget on the right side of the screen titled "Audience Activity". This widget will show you the total visitors who have joined and left the audiences based on the date range selected. The date range can be changed by clicking on the settings "sprocket" in the bottom right of the widget. You can read more about the AudienceStream Dashboard here.