What are "Impressions"?

For dynamic SmartPromos, we define an impression as an ad being delivered to a user via the dynamic ad insertion platform. 

For baked-in SmartPromos, we define an impression as a download of an episode containing the ad. 

Chartable uses the industry standard (IAB 2.0) definition of a download: a device (a unique IP address and user agent combination) that downloads enough of an episode audio file to playback at least 60 seconds of audio. 

Nonetheless, there are a lot of areas that are open to interpretation in the IABv2 guidelines, which can lead to discrepancies even among hosts that are certified. Here are some of the choices we’ve made, along with other common reasons why Chartable’s numbers might differ from your publisher's hosting provider:

1. History. Our analytics prefix can only track downloads from the moment it’s been installed. So if it’s installed at noon, it’ll only collect downloads from that time forward, and the first day will have only partial data.
   
   This also means that our numbers for episodes released before the prefix was installed will differ, because there will be a gap between the time the episode was released and when we started seeing downloads. 
2. Download windows. We define unique downloads on a calendar day in the UTC timezone per the IABv2 guidelines. The publisher's hosting provider may not deduplicate unique downloads, in which case our numbers will be significantly lower. Or that provider may use a different time period for unique downloads, such as a rolling 24-hour window, a 1-hour window, or a 24-hour day in a different time-zone.
3. Blacklists. We don't count all downloads from known datacenter IP ranges (e.g. AWS, Azure) or other IPs or user-agents that trigger our abuse detection systems. This affects some podcasts more than others. Some hosting providers may not use a blacklist, or may use a different one than ours.
4. Whitelists. The IAB guidelines allow vendors to implement a whitelist for known “high-density IP addresses” like dorms and corporations. We don’t use a whitelist because identifying these IPs seems to us a manual and potentially error-prone process. The publisher's hosting provider may differ.
5. Embedded players. Some hosting providers, including Soundcloud and ART19, don’t allow for analytics prefixes like ours in their web-embedded episode players. If you rely heavily on these players, our numbers may differ because we can’t “see” these downloads. For example, we can "see" downloads on Soundcloud-hosted feeds, but we can't see the plays that show gets from people playing it directly on Soundcloud.com. As you'd expect, this is usually a pretty small fraction of the show's total listens.