The number of Americans who have downloaded a podcast rose only slightly in 2007 despite growing awareness of the media format, a study published this week found.

Only 13 per cent of those polled had "ever" downloaded an audio podcast, up from 11 per cent last year, according to the findings Edison Media Research presented to the Corporate Podcasting Summit in London on Monday.

The number of people who had downloaded a video file also rose, from 10 per cent last year to 11 per cent in 2007.

By comparison, the poll said awareness of the media format grew from 22 per cent in 2006 to 37 in 2007.

A podcast is an online audio, video or multi-media program internet users can download as a digital file and listen to on their computer or MP3 player.

Edison researcher Tom Webster admitted on the company's website that the figures were lower than people in the industry expected.

"Certainly, given the impressive growth in awareness of the term 'podcast,' one might have expected more than a two percentage point increase in the behaviour," he wrote.

But he suggests that while the audience is small, it has similar penetration to Satellite Radio.

"Podcasting now teeters at the edge of the chasm on the consumer adoption curve, with mainstream adoption across the other side," he wrote.

The stats come from 1,855 telephone interviews in January 2007. A study by the Pew Internet & American Life Project last November put the U.S. podcast audience at 12 per cent and found one per cent of internet users are downloading a podcast on a typical day.

First podcasts started in summer 2004

Podcasting is a relatively new phenomenon that started in late summer 2004. Among digital audio formats, podcasts are unique in that they can be downloaded automatically using software capable of reading feed formats such as RSS (Really Simple Syndication).

Within six months of its inception, programs available through podcasting grew from about three dozen to well over 3,500.

While early podcasters typically distributed syndicated audio files and radio shows, podcasters now routinely deliver many kinds of digital multimedia content, including video, images and text.

In 2005, the New Oxford American Dictionary declared "podcast" the word of the year, with the accompanying definition of a podcast as "a digital recording of a radio broadcast or similar program, made available on the internet for downloading to a personal audio player."