Podcasts, once a curiosity, are now big business: An industry forecast says they'll draw $220 million in ads this year.

Why it matters: A new Interactive Advertising Bureau study also found that while three-quarters of podcast ads are direct-response (like ordering on Stamps.com), there's been an increase in brand awareness ads. These are the ads you typically see aligned with high-quality TV/video content.

How it happened: The growth reflects an audio streaming boom, made possible largely through mobile apps like Apple Music and Spotify.

The audience: Edison Research and Triton Digital estimates 98 million U.S. adults listen to podcasts.

For kicks: Consumers prefer host-read ads over pre-produced ads 60%-40%, according to the study.