Chris Jolocon
Member
I recently did a live event where the audio was clean 97% of the time except for a few short segments - anywhere from 5 seconds to 30 seconds, perhaps 5 or 6 instances altogether - where the signal suddenly dropped in level, approx. 15-20 db, and distortion introduced, then the signal would return to clean and healthy level. This was video recorded, so I was able to compensate for the level drop in post, in video editing, but not the distortion. When I tested the same equipment after the event but in an indoor space I could not recreate any of the issues experienced at live event. My initial sense is that this was either an electrical issue, possibly causing artifacts or a temporary drop of phantom power, or there was some sort of RF or EM interference. For the audio samples below the level drop has been compensated, but you can still hear the distortion:
Audio Sample 1:
Audio Sample 2:
Here are some details of setup.
Outdoor event at football field.
Audio Technica shotgun mic at lectern, approx. 150ft. of XLR cable to a 75' snake, over metal bleachers up to a press box (metal structure), to an Allen and Heath ZED 12fx mixer. Mixer provided the phantom power. Audio signal sent back down to field to loudspeakers and a video camera.
For some stretches audio and power cables were next to each other (I know this is a no-no).
The mixer was within a foot of an iMac computer.
We were close (200 yards) to high-powered electrical lines.
audio cables were run on top of metal bleachers and mixer/computer were within a metal "press box".
Since mixer was feeding a live stream, a video camera on field, and the loudspeakers on the field, I realize this essentially ties all these components together. I wonder whether some sort of malfunction or interference with any of the connected devices caused the audio issue.
Other oddities occurred at same event:
I have boxes that send HDMI signal over longer stretches of Cat6 cable. One set of such boxes did not seem to work at all, and with another set the signal was at first intermittent, but thankfully for the event itself worked consistently. The Cat 6 cable was not shielded, but I am not certain that was the issue. We were within specifications for the length of the Cat6 runs and the converter boxes.
The Video camera recorded 2-3 blank frames at one point (all green). This has never happened before. The audio was also out of sync by a few frames, which has never been a problem in previous events.
One of the 4 loudspeakers on field died at some point between testing the day prior to the event, and the setup time day of event. I was able to replace it with a different loudspeaker, but original unit still does not power on (it was a fairly new QSC k series speaker).
Everything was on Furman power strips, offering basic surge protection and RF /EMI rejection, but not the more robust features of their power conditioners.
During the event I set up a wireless mic in case the issue got worse, but it actually went away for the 2nd half of event. When I scanned for open frequencies there were barely any found. Sennheiser evolution 100 series, normally finds many available frequencies.
I would like to identify the cause. If I had to do the event again I would try these things, but I'm not 100% sure they would prevent the same issue:
Use AA battery on board the condenser shotgun mic, to avoid running phantom through a long XLR run.
Use shielded cat 6 cable
Use an RF inline filters (XLR barrels, Sescom and Shure make such a product)
Keep mixer away from iMac computer
Separate all audio and power cable runs.
Any ideas whether this seems like a phantom power issue or electrical issue, or RF or other type of interference?
Audio Sample 1:
Audio Sample 2:
Here are some details of setup.
Outdoor event at football field.
Audio Technica shotgun mic at lectern, approx. 150ft. of XLR cable to a 75' snake, over metal bleachers up to a press box (metal structure), to an Allen and Heath ZED 12fx mixer. Mixer provided the phantom power. Audio signal sent back down to field to loudspeakers and a video camera.
For some stretches audio and power cables were next to each other (I know this is a no-no).
The mixer was within a foot of an iMac computer.
We were close (200 yards) to high-powered electrical lines.
audio cables were run on top of metal bleachers and mixer/computer were within a metal "press box".
Since mixer was feeding a live stream, a video camera on field, and the loudspeakers on the field, I realize this essentially ties all these components together. I wonder whether some sort of malfunction or interference with any of the connected devices caused the audio issue.
Other oddities occurred at same event:
I have boxes that send HDMI signal over longer stretches of Cat6 cable. One set of such boxes did not seem to work at all, and with another set the signal was at first intermittent, but thankfully for the event itself worked consistently. The Cat 6 cable was not shielded, but I am not certain that was the issue. We were within specifications for the length of the Cat6 runs and the converter boxes.
The Video camera recorded 2-3 blank frames at one point (all green). This has never happened before. The audio was also out of sync by a few frames, which has never been a problem in previous events.
One of the 4 loudspeakers on field died at some point between testing the day prior to the event, and the setup time day of event. I was able to replace it with a different loudspeaker, but original unit still does not power on (it was a fairly new QSC k series speaker).
Everything was on Furman power strips, offering basic surge protection and RF /EMI rejection, but not the more robust features of their power conditioners.
During the event I set up a wireless mic in case the issue got worse, but it actually went away for the 2nd half of event. When I scanned for open frequencies there were barely any found. Sennheiser evolution 100 series, normally finds many available frequencies.
I would like to identify the cause. If I had to do the event again I would try these things, but I'm not 100% sure they would prevent the same issue:
Use AA battery on board the condenser shotgun mic, to avoid running phantom through a long XLR run.
Use shielded cat 6 cable
Use an RF inline filters (XLR barrels, Sescom and Shure make such a product)
Keep mixer away from iMac computer
Separate all audio and power cable runs.
Any ideas whether this seems like a phantom power issue or electrical issue, or RF or other type of interference?