An extensive study by NPR Labs points to significant trade-offs between the audience reach of digital HD Radio and the amount of interference to analog FM. Even though its transmission power is just 1 percent of analog FM’s, its range for listeners in cars comes close to equaling analog, the CPB-funded study found. But HD reaches areas including little more than one-third as many indoor listeners. To extend its range, the National Association of Broadcasters in January joined other industry groups advocating an optional power boost for HD Radio, permitting stations to emit digital signals at 10 percent of analog transmitters’ power. The FCC has not yet begun a proceeding to consider the change.