Sound Pitch and Rate of Fire between the automatic fire (1:11 through 1:21) is totally different than (11:06 through 11:26), if you are unable to discern the difference then we cannot help you.
At the (13:11 though 12:32) - Best guess is the burst fire is coming from a suppressed M4 running subsonic ammunition, fired from a position of cover and concealment very close as subsonic rounds are unstable. Something like this: https://youtu.be/wc0EQ4quVQQ
In the comments being held for idiocy, ignorance, or general trolling behavior, there seems to be significant confusion (Paid Troll / Shill or Genuine Ignoramus) on the acoustics; specifically the echo and also behavior of supersonic vs subsonic, and sounds associated with the sound barrier.
Here is a simple video which explains the acoustic difference between suppressed subsonic and suppressed supersonic fire: https://youtu.be/Icrm9m9bRpY
The key to understanding this issue:
1. Understand the Cyclical Rate Variation between weapon systems - the "Acoustic Signature"
2. Understand the Change in Sound specific to the "Origin of Fire"
3. Recognize and Identify Changes in "Rates of Fire" or "Cyclic Rates"
4. Recognize and Identify Changes in the Sounds directly resulting from different firing locations. Here is another example video, again, of two different firing locations, if you are unable to determine for yourself the fact there are two separate locations, then we cannot help you...https://youtu.be/fEf7HObspB0
5. Two different Cyclic Rates taking place concurrently is conclusive evidence of multiple shooters, multiple weapon systems, from multiple locations. You will hear the evidence for this At the (13:11 though 12:32) of this video.
6. The idea of a "Bump Fire" or "Gatling Device" on a modified AR-15 is a joke (As stated Earlier) - It is possible this could have been used as "Acoustical Cover" for the precision bursts of one or more suppressed weapon systems firing subsonic ammunition from a very close position. (As Stated Below) In the below Interview, Mike Cronk provides the statement that his "buddy" was shot 3x in the chest. This type of wound pattern is entirely inconsistent with a "bump fire" slide on an AR-15 from 518M Distance (Meaning Impossible)...and is entirely consistent with the suppressed controlled bursts at shorter range identified in this video. https://youtu.be/6jvITJEm_jw
7. Echo is just that...an echo...an echo will not introduce concurrent conflicting cyclic rates of fire...sorry, but no. Two separated firing positions are easily discernible from an echo...if you cannot discern between the two, then again, we cannot help you...
8. There are active trolls pushing false explanations, trying hard to muddy the water, so beware. Use common sense.
9. Download this and other videos, share links, then repeat the process.
10. We desperately need first hand testimony of the entry and exit wounds of the dead and wounded (Impact Groupings, Bullet Spread, Caliber, etc..) from First Responders, EMT, Police Officers on the Scene, Fire Fighters, ER Nurse, ER PAs, ER MDs, etc...from those who personally treated the dead and / or wounded. If you are out there please provide your detailed testimony ASAP. (there is no reason for this to be withheld or classified information). - Share with anyone who can provide first hand detailed testimony specific to the entry and exit wound patterns.