But the singer admitted that she's having a much better time in her recording sessions since giving birth to her second child, Remington, back in April.
Asked what's "been the best day in the studio so far," Clarkson replied: "Girlfriend, coming back from being pregnant."
"[It's] a weird thing for your diaphragm -- even how you breathe normally," she told Entertainment Weekly.
"Apply that to singing, which you need a ton of breath for. It’s just a different thing to build back up," she admitted.
Remington is the second child for Clarkson, 34, and husband Brandon Blackstock. The couple, who wed in 2013, are also parents to 2-year-old daughter River Rose.
"Two weeks ago, I was doing lead vocal on this song that I am just in love with in this studio in my house, and the producer was here, and I flipped out," she recalled. "It’s funny because it’s on camera. We’re filming all of it. It’s the day my voice came full-on back, like exactly what I wanted."
"I sounded amazing. I was so excited. My producer was laughing so hard because I was freaking out," Clarkson added.
For fans who may be wondering why Clarkson is recording a soul album, the singer told EW that she's "always wanted to make this album and I just haven’t been able to."
"While it is still pop, it’s way more soulful," she added. "The sound is so innate in me. It’s just so natural. It’s like, 'God! You should have been making records like this the whole time.'"
"And I love making all different kinds of records, so it’s not like I’m mad about it or anything," Clarkson continued. "I’ve just wanted to make this particular record since I was in junior high."