UPDATE: A footnote in Triton Digital's February 2012 Webcast Metrics report notes that audience figures for both Slacker and Pandora are lower than they should be. Slacker's audience is "understated," writes Triton, due to "a collection system migration" in Febraury. Meanwhile Pandora's audience is around 4.5% smaller than it should be "due to a collection node failure in February." That would put Pandora's month-to-month growth at around 10%, rather than the 6% reported in our original coverage below. -- MS

Pandora and Clear Channel saw strong audience gains in February 2012, according to Triton Digital's new Webcast Metrics report. Most other broadcasters and webcasters in the Top 20 ranker grew their audiences as well.

Pandora's AAS (Average Active Sessions, which is essentially equivalent to AQH — i.e., average simultaneous listeners) reached 1,066,500 in February, according to Triton's Domestic Mon-Sun 6a-12m daypart ranker. That's up 6% (or 56,533) from January 2012 and 115% year-over-year.

Meanwhile #2-ranked Clear Channel posted a 13% month-to-month growth, reaching an AAS of 160,903. The broadcaster's AAS is up 92% year-over-year.

CBS Radio, which holds the #3 spot (bumped out of second-place in October 2011 by Clear Channel), declined 2% from January 2012 to reach 61,983. That's down 38% year-over-year.

Slacker's AAS (38,966) declined 19% from January 2012 (though this figure is "understated," see our update above). It's up 36% from February 2011.

Most broadcasters in the Top 20 list saw month-to-month gains, including Radio One (up 13%), Univision (up 11%) and Cox (up 6%).

(The chart above shows the growth of Pandora, CBS, Clear Channel, the top 5 terrestrial radio groups and Slacker from September 2009 through February 2012. Note that Pandora's AAS numbers from December 2010 through mid-August 2011 were affected by the omission of tracking code in some of its mobile apps. Click to view in full size.)

The combined February 2012 AAS of all streamers in Triton's Top 20 ranker (1,514,378) is up 6% over January 2012 and 75% year-over-year.

You can find the Domestic Mon-Sun 6a-12m ranking below. Find out more from Triton Digital’s Webcast Metrics report here (PDF) and find our coverage of January 2012’s ratings here.