In Omny Studio you'll find a suite of analytics and metrics. To go beyond download numbers, Omny also provides an estimate for your number of unique listeners, and the number of unique IP address, for the selected time period in clip, program, network or organization-level analytics.
You can find this figure from the top of your analytics pages in Omny, whether that's at the Clip/Program/Network/Organization level.
Just select the date range you want to see the Estimated uniques for.
Estimated uniques are "an estimated number of unique users who downloaded for the selected time period."
You can select either an estimated number of unique listeners.
"Listener is an IAB metric represented by a combination of IP address and user agent."
Or, an estimated number of unique IP addresses.
"IP addresses may under-represent multiple people downloading from a shared home or office."
Your Estimated uniques are a great way to go beyond your downloads to determining your audience size. Another analytics tool available to you is the data available from certain podcast apps, specifically Apple and Spotify;