Speaking at The Radio Academy's 'Commerce in Commercial Radio: Who Pays the Bills?' event last night, Smith said: "In the short term it would help commercial radio and it would accelerate the rate of growth."
The Digital Economy Act, which became law on 12 April, provides for a transition from analogue to digital radio.
The major FM stations will move across to DAB two years after a number of criteria have been met, including 50% of all listening is via a digital platform.
Smith said the RAB believed radio will account for 7% of media spend in three years, up from 6% today. Smith said: "The RAB's business plan focuses on the advertisers that are spending less than 7% and then on what we have got to do to make sure they do [spend 7%]."
However, Dominic Woolfe, director of radio, outdoor, press and cinema at Publicis media agency Starcom, and Richard Jacobs, head of commercial strategy at GMG Radio, said radio will have "done well" if it remains a 6% medium three years from now.
Stan Park, chairman of the radio specialist RadioWorks and chair of the event, asked the panel whether WPP's dominance of the radio buying market will have a big impact on how radio is traded.
Jacobs, who recently joined GMG from WPP media agency MediaCom, where he was head of radio, said: "It takes a brave sales director to walk away [from WPP]. But if you don't say no then you set a precedent that will allow them to come back next year and ask for cheaper rates again."
Jacobs said radio groups should focus on "creating value for advertisers" and Woolfe cited Blackberry's sponsorship of the Kiss breakfast show as an effective radio campaign.
Woolfe said: "Blackberry don't talk to me about cost per thousand. They talk to me about how many people are going out and buying Blackberries."