As the did she or didn't she? controversy continues
 to swirl around Beyoncé's performance of the national anthem at President Obama's inauguration,
 veteran recording engineer Ian Shepherd feels pretty confident in his judgment about what happened on Monday afternoon.

"At least half of what we were hearing, if not all, was her real vocal," said Shepherd, who has been writing an ever-evolving blog on the flap, in which he's broken down the evidence in a Zapruder film-like way.

There continue to be conflicting accounts
 of whether Beyoncé was singing live, singing live to a pre-recorded backing track, lip synching to a pre-recorded backing track, or some hybrid of the three. Shepherd, though, has no doubt that she was singing live to a pre-recorded track. "The band were miming, and they said they were miming," said Shepherd, who has more than 15 years of audio engineering experience, including testimony in copyright infringement cases and work on CDs and DVD by the artists including Keane, the Royal Philharmonic Orchestra, New Order and King Crimson.

On his blog, Shepherd points to two different videos of the performance, one from the Wall Street Journal and the other from the New York Times, in which subtle differences point to a live take. "On the Journal video you can hear that there are two different vocal versions happening," he said. "One of them looks absolutely as though she's singing live and the other is a pre-recording." The only question in his mind is whether Beyoncé wanted to use the version she recorded as a safety with the Marine Band or whether she wanted her live vocal to be used. A spokesperson for the Marine Band acknowledged that an instrumental recording was used because Bey didn't have enough time to rehearse before Monday with the band. "No one in the Marine Band is in a position to assess whether it was live or pre-recorded," the official said of Beyoncé's vocals.

"With an event of this size, I would understand that you would want to play it safe and have a recording that she would be practicing with on her laptop so that she would know it inside and out and have the timing down," Shepherd said. "It is very hard for a band to play in tune when the temperature is so low ... I used to play trombone and I know that as the brass instruments are played they warm up and everyone can go in and out of tune with each other. So I can understand why everyone would want to use a recorded [instrumental] track."

But Shepherd said he doesn't buy reports that her microphone was turned off because in the Journal video he can hear her live vocal and the backing track playing at the same time.

Among the other evidence he cites for a live performance: »When Beyoncé starts singing, her vocals are hard to hear because the microphone is set too low, an issue the sound person quickly corrects. If it were a recording, this issue would not be audible.

»At 1:16 in the Times video, Shepherd noticed a slight head tilt toward the microphone as the sound gets more bassy, a result of an acoustic quirk called the "proximity effect."

»At 1:52, she takes out her earpiece, which some people have cited as proof she was lip synching. But Shepherd told MTV News that it's actually evidence she was trying to hear what her voice was doing in the "real" world as she kept the audio feed of the recording in the other.

»At 2:17, Beyoncé smiles, which Shepherd said you can "hear" in her voice.

»At 00:36 in the Journal video you can hear the wind blowing and making a popping sound on the microphone as the singer's scarf flies around her neck.

Spokespeople for the singer have not responded to requests for a comment on the controversy.

The scarf flapping sound alone is enough to convince him that Beyoncé had a live mic, but he said in the Times video, just before the "rockets red glare" line and the earpiece pull, you can clearly see something is distracting the singer and she needs to hear what's going on better. "Once she pulls the earpiece out she looks more relaxed and happy ... she looked uncomfortable and uncertain before that."

In his previous expert testimony in copyright cases, Shepherd said he often couldn't rely solely on audio quality to make a judgment and has to look for quirks in performances to decide.

"She's so good that her pre-recorded and live vocal are almost identical," he said. "That's why it's so hard to figure out and that's why you look for quirks or technical issues. There's a microphone pop on a 'p' in one of the words on all the versions. That to me says it happened in the live version, because that's something that would be fixed in the studio version."

"When you add up those tiny little details it's pretty clear ... at least half, if not all of what we were hearing is her [live] vocal. All these clues point to me to the live vocal being in the mix and that's what she wanted."