NEW YORK (CBSNewYork) — On what would have been Frank Sinatra’s 100th birthday, one of his close friends is opening up about the man and his legacy.

Francis Albert Sinatra was born Dec. 12, 1915 in Hoboken, New Jersey.

“The hullabaloo around Frank Sinatra’s birthday is valid, necessary and significant,” WNYC broadcaster Jonathan Schwartz, who was dear friends with Frank Sinatra, told WCBS 880’s Sean Adams.

Schwartz said Sinatra’s legacy is vast.

“He took the American songbook and said to it, ‘No songbook, you come with me,” Schwartz said. “Without Sinatra the form of those songs would’ve died off far more quickly and they haven’t died off because of him, these albums sell.”

So what made Sinatra so special?

“He was terribly honest as a singer, he spoke the truth in his singing,” Schwartz said. “Sinatra was the great interpretive singer who ever lived, meaning he interpreted the songs written by other people.”

They shared many conversations about music and Schwartz said Sinatra cared deeply about his songs.

“We had long talks together about his own music, about his own albums, and about the possibility of this song or that,” Schwartz said. “I have many hours of session tapes where you can hear him crafting his work, suggesting to the orchestra what should be and not be.”

There was his public persona, but what was Sinatra really like in his quiet moments?

“He read a great deal, wanting to understand a greater world, he also listened to classical music a great deal. Two of his favorite composers were Stravinsky and Puccini,” Schwartz said.

And like those musical masters, Sinatra endures.

“I do believe as time goes on, the American songbook will have a wonderful resurrection and holding the screen to the resurrection will be Sinatra,” Schwartz said.