You can hear canon fire (artillery gun fire) in the C-SPAN video after 35:00
https://www.c-span.org/video/?508135-3/president-biden-2021-inaugural-ceremony
It is faint and hard to hear; it sounds like directional mics are used perhaps with noise canceling so you've got to discern the blast and report from the noise. But they're in there, timed about 3-5 seconds apart.
Note that other noises make similar sounds. It would be helpful to run this through an equalizer or DSP to bring out the sharp upper harmonics and see if there are in fact 21 of them.
I dont hear it
I remember that moment. I can also do not hear the canons but that awkward minute struck me on 20th. Everybody looks around ... like asking ... is now the time all of us get arrested? Might well be that they were waiting for the battery to finish.
The reports are louder than the blast (35:11) and it's absolutely in the noise floor. I'm a ham radio op and accustomed to pulling weak Morse signals out of the mud, but they're in there. Per another comment, there are definitely chairs clanging and other noises.
Listen for the characteristic "chum-Kow" sound of the echo. It's not the "backwards" sound you hear from a supersonic round hitting the berm at long range. It's that the echo is picked up by the mic's forward sensitivity gain while the direct sound is attenuated as you'd expect in a cardiod pattern. (I don't see any long distance shotgun style mics at the podium. Just standard sound system units.)
Yeah. I'm a shill.
Whatever.
Don't criticize the democrats for their enforced demand to adhere to the reigning orthodoxy.
No deviation permitted. Toe the party line.
Kamalas queef