The Commission on Presidential Debates said Friday that the first debate on Monday was marred by an unspecified technical malfunction that affected the volume of Donald J. Trump’s voice in the debate hall.
Mr. Trump complained after the debate that the event’s organizers had given him a “defective mike,” contributing to his widely panned performance against Hillary Clinton. Mrs. Clinton lampooned Mr. Trump’s claim, telling reporters on her campaign plane, “Anybody who complains about the microphone is not having a good night.”
Mr. Trump was clearly audible to the television audience. And there is no evidence of sabotage. But it turns out he was on to something.
“Regarding the first debate, there were issues regarding Donald Trump’s audio that affected the sound level in the debate hall,” the commission said in its statement.
The commission, a nonprofit organization that sponsors the presidential debates, released no other information about the malfunction, including how it was discovered, which equipment was to blame, or why the problem was admitted to only on Friday, four days after the debate.
Reached by phone, a member of the commission’s media staff said she was not authorized to speak about the matter.
Some members of the audience, held at Hofstra University in New York, recalled in interviews that the amplification of Mr. Trump’s voice was at times significantly lower than that for Mrs. Clinton. And at times Mr. Trump appeared to be hunching down to get his face closer to his microphone.
Zeke Miller, a reporter for Time Magazine who attended the debate, mentioned the difference on Monday in a report to the traveling press pool for Mr. Trump. From his vantage point, Mr. Miller wrote, Mr. Trump was sometimes “a little quieter” than Mrs. Clinton.
In an interview, Mr. Trump said he had tested out the audio system two hours before the event and found it “flawless.” Only during the debate did he notice the problem, Mr. Trump said, and he tried to compensate by leaning down more closely to the microphone. He complained that the changing volume had distracted him and alleged again that someone had created the problem deliberately.
“They had somebody modulating the microphone, so when I was speaking, the mike would go up and down,” Mr. Trump said. “I spent 50 percent of my thought process working the mike.” He had wanted to pause the debate to address the problem, Mr. Trump said, but felt he could not. “How can I stop the show if I had 100 million people watching?” he said.
Asked whether he was reconsidering participating in the next debate, scheduled for Oct. 9, Mr. Trump did not answer directly.
“I want to do the next debate, but everybody is talking about the mike,” Mr. Trump said.