Google has taken the next step in its conquest of traditional media with a new beta test of Google Audio Ads. A group of 20 advertisers have already begun buying ads on terrestrial and satellite airwaves under the experiment.

Google Audio Ads are sold on a CPM basis through the AdWords platform, and advertisers can target on factors like geographical market and time of day. Reporting functions disclose which stations ran ads and when, and real-time air checks are available, a bit of a novelty for interactive marketers who have grown used to not seeing their non-search executions.

Effectiveness metrics are the old-fashioned kind, including analysis of call volume and in-store traffic.

"If somebody's running a campaign spanning three metro markets and they're getting great call volume, they have the ability... to modify the campaign or heavy up," said Ryan Steelberg, head of radio operations for Google.

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