It's the sound of silence that Josh Groban finds hardest to hear during the pandemic.

Quarantine hasn't stilled his voice or songwriting, but the give-and-get Groban usually enjoys from interacting with his audience is gone. He sings into a machine and hears nothing back.

"When the song is over, to have silence is so weird," he said. "The back and forth that I love so much, chatting with the audience, going into the crowd — I've had to fill in that gap in my head."

Groban is doing his best to fill the void with a new album due in November and three themed live streaming concerts, starting with...