NPR hopes the FCC approves the multichannel concept for HD Radio early this year.

In perceptual test results submitted to the commission this fall of HD Radio's coder at various bit rates, NPR said, "The new testing indicates that 48 kbps is perceived by most listeners as providing equal sound quality to the maximum rate of 96 kbps."

Optimum bit rate allocation varies according to format, so NPR hoped the agency would allow stations to determine their own bit rate allocation for multicasting.

The codec tests showed it was possible to achieve two near-CD quality channels, plus up to four additional voice-grade channels with minimal, if any, interference to existing analog radios, NPR's Mike Starling told RW Online. Twelve codecs from nine vendors were tested.

In the initial tests last year, the main channel was 64 kbps and the supplemental channel was 32 kbps.