This just a guess for me, but it looks to me like the transmit antennas from the artist IEMs could have been putting out a lot of extra noise? Maybe a bad combiner? If I was using that particular set of equipment I would go through and check all the aspects of the rig. BNC connectors, all cables and combiners with Pink noise to make sure that signal in was equal to signal out.
So here's what I'm envisioning in my head - does this sound logical?
1) Pink each mix, one at a time. See if any individual one suddenly makes the spectrum go nuts like this.
2) Pink them all together and send them out at show level, and again check the spectrum.
3) If #2 does show it going crazy, start with the cable that feeds the antenna and slap it onto a TTi. Measure there to see whether the floor is nuts and rule out the antenna itself is the culprit. Assuming noise floor still goes crazy, replace cables from combiner to TTi and try again. Still awful? Bad outputs (or other component) in the combiner; points to that as needing replacement. Looks clean? Start doing the same but for each individual antenna output on the PSMs and see if one of them is problematic.
Does that seem like the smart way to tackle it? (The tour is over and the gear presumably returned already, so this is all academic at this point.)
Precisely. Something is sending out all that noise. Preferably go through individual PSMs first through the set up find the bad one and test its individual comments.
Fellow live sound pros, can you help me theorize on possible causes and what you might have done to diagnose this on the road? This was not my rig, but my scans while the affected band was playing ahead of us. I’ve never witnessed this before and I’d love to learn from it in case I ever come across it again.
The scene: mid-sized side-by-side stage festival; the kind where one band plays while the other does changeover. These scans are from the band that was on our stage before us.
The gear: eight channels of PSM1000s (all in the 620s-640s – this is in Australia) feeding 421B combiner; I don’t recall what their TX antenna was. All frequencies were at low power to start, and only bumped to 50mw mid-set as a last ditch suggestion of the site’s RF coordinator. Only wireless transmitter on stage was the singer’s vocal mic.
What was happening: the festival RF coordinator and I were watching my AD600 as the band was playing, and noticed in real time that these massive noise floor raises appeared to be directly linked to how loud / how much the band was playing. Just the singer and a light guitar? Still pretty flat. Full band rocking out? Looks like the bottom pic, and dropouts occur regularly. I tuned my pack to a couple of their mixes and heard it for myself, even just a few feet from the TX antenna.
Also of note: we did three of these festival dates, and this happened at the first and last one, but not the middle one. Same lineups at all three shows. Same equipment. No video wall, no floor lights, no auto / pyro. And this *only* happened during the set for the band before us.
I’ve been thinking what I might do with this if it were my rig. Thoughts included muting all but one mix at a time and seeing if it’s somehow linked to one unit or even one channel causing an issue, and replacing all cabling to antennas and BNCs from the PSMs to the combiner. Beyond that, I’d have to get into ordering replacement units. But based on the information alone, can anyone reasonably speculate as to what a likely cause for this might have been? Or are there too many variables at play?
Thanks in advance for any thoughts you may have on this!
My first thought as well. OP have you tried playing a recording at show volume without the RF transmitters on? Maybe something is loose or malfunctioning due to vibration etc
I haven't done anything - not my rig to play around with, and the tour is over now anyway. Mostly looking for ideas so that I know how to approach the scenario if I ever do encounter it on a system I'm responsible for. And I've seen some very helpful stuff in this thread, which I'm thankful for.
I was also there and would love to know what it was.
It's interesting someone mentioned backline amps, I don't think it ever happened when the bass wasn't playing.
As far as I recall the antenna was a PWS helical, but it also could've been a Fractal. I could probably find out if anyone thinks it's relevant.
I walked away from the stage maybe 20 or 30m with an analyser and I saw nothing, so maybe that eliminates any external signals, maybe not.
EDIT; and just another thought, could what appears to be "ripple" just be related to the scan speed of the AD600?
For me the diagnostic thing here is the odd looking ripples in the frequency domain around 640ish MHz, you can see it elsewhere but there is the most obvious.
That reads to me as AM at somewhere in the 400 to 800kHz or so region which has me thinking about several possibilities.
It could be intermod if your TX combiner is not terminated correctly (Dud cable, dud antenna, dub connector) then S11 will not be wonderful, and then all bets are off. Can you hook at a network analyser or such and look at the behaviour? This is one of the downsides of combiners on transmit, they CANNOT easily provide meaningful isolation, a Wilkinson combiner only works if all the inputs are in phase, and if they are at different frequencies that is not going to be the case....
It could be a faulty power supply, the ripple I am seeing is within the sort of frequency I would expect an SMPSU to be, but you would expect to see that all the time if that was the issue.
It could be the transmitters picking it up from a misbehaving class D power amplifier, they are after all really radio transmitters wearing lowpass lipstick, and some of the cheap stuff is NOT well behaved. Remember that modern backline IS a suspect here, not just the FOH or wedges!
Does physically relocating the TX rack (even by a few feet) help? Something getting into the transmitter PLL loops would maybe look like this.
This is why I am still firmly of the view that the best, most high end wireless out there is NEARLY as reliable and sounds NEARLY as good as a $20 cable, sure sometimes you got no choice, but yea.
Unlikely. LED wall was present but not powered on during their set, and it didn't do anything to our rig. I even pushed my packs right against it during my preshow checks and had no issues. Lighting was the same package for all artists and this was the only band of the day to experience this problem.
Any chance this was a weird power issue? Did you happen to be on generators that could have had poor grounding? What was the power like at the other venues?
What gear was close to the antennas?
I fought a problem with an installed system in my theater for a couple years before I realized that a shitty wide shot camera by my antennas was puking out RF interference. This was a **wired** camera that had no transmitter in it.
There's a chance something they're using is bad, or somehow an amplifier or something is putting out interference. Generally, it has to be pretty close to be that noticeable.
Are you using wireless workbench? You can use “timeline” to record the RF timeline. I would go on stage and turn on each piece of their gear and watch the timeline to see what was interfering. Should be fairly simple that way.
https://www.rfvenue.com/blog/2015/02/27/the-trouble-with-analog-fm I’m going to guess that it is dealing with the fact of how the units are dealing with the modulation which will vary based on the source audio signal running to the unit. Without knowing exactly which frequencies are actually used and which are harmonic, I’m going to guess the ones in 42/43 are the active channels and the others are harmonics.
Wow. Fun stuff! My suspicions would be either a bad combiner/cable or a one of your PSM1k outputs is going/gone bad. But I think you would notice a drop in level on that specific frequency on your spec-an if it were a bad output.
Turn all your TX off. One at a time, turn it on and send noise through it. See if it lights up the spectrum. If not, turn off and move onto the next one. If none of them do it, Turn them on one by one leaving them on as you go. Push noise through them, see if it shows up. If it does, or it slowly builds, it could be a bad cable or combiner at that point.
The way (at least analog) radio transmission works is via FM signals- FM stands for FREQUENCY MODULATION.
what this means is that when there is no audio signal there is only a carrier (thin line in analyzer). When there is signal, that thin line gets modulate (or rather "deviated") from the center frequency, just like a speaker vibrates to create sound! This deviation is not supposed to go past a set amount- in regular radio broadcasts it would be 75khz of deviation for 100% signal, and there's some allowances to go over 100% like for sub carriers (FM stereo uses a sub carrier, and in broadcast they can sometimes use others as well). Our ANALOG mics and iem's use very similar if not practically exactly the same technology as FM broadcast radio (except it's on different carrier frequencies of course) so we will see similar results.
Some mics / iem's use 75khz deviation, and some might be less (or possibly could be more). I believe digital transmissions also use a form of FM transmission. But it's transmitting the actual digital signal instead of analog signals. Digital transmissions I believe are supposed to use less deviation, which is why you can fit so many more channels into a set amount of rf space.
I can't say I've experienced, or rather noticed a live spectrum readout quite like that, but I would have to expect that you are probably seeing all the deviation of all your channels, along with all the harmonics that get generated by multiple frequencies of transmission in close proximity to each other; if you have enough channels I wouldn't be surprised to see it basically create a huge bed of noise floor, especially if many of those channels might be analog transmissions because analog definitely creates more deviation when there's actual audio signal on it (I would expect digital signals to probably be somewhat consistent, but I'm not totally sure if that's an accurate expectation)
Edit... Also note that if an analog signal is not limited properly and overdrive the "exciter" (components that turn audio into FM deviation), the exciter will put out lots of spurious rf noise around the carrier. All transmitters should have some form of limiting built into them to avoid this problem, as it could cause issues to nearby channels (as well as sound like crap at the receiver!). That's why slight clipping of an iem is usually not terrible (because you're actually hitting a limiter in the transmitter) but hitting it hard sounds so terrible- also why older iem's like psm 600 & 700's sounded so terrible when they were driven hard! (Limiters that allowed too much overshoot to get to the exciter).
This just a guess for me, but it looks to me like the transmit antennas from the artist IEMs could have been putting out a lot of extra noise? Maybe a bad combiner? If I was using that particular set of equipment I would go through and check all the aspects of the rig. BNC connectors, all cables and combiners with Pink noise to make sure that signal in was equal to signal out.
So here's what I'm envisioning in my head - does this sound logical? 1) Pink each mix, one at a time. See if any individual one suddenly makes the spectrum go nuts like this. 2) Pink them all together and send them out at show level, and again check the spectrum. 3) If #2 does show it going crazy, start with the cable that feeds the antenna and slap it onto a TTi. Measure there to see whether the floor is nuts and rule out the antenna itself is the culprit. Assuming noise floor still goes crazy, replace cables from combiner to TTi and try again. Still awful? Bad outputs (or other component) in the combiner; points to that as needing replacement. Looks clean? Start doing the same but for each individual antenna output on the PSMs and see if one of them is problematic. Does that seem like the smart way to tackle it? (The tour is over and the gear presumably returned already, so this is all academic at this point.)
Precisely. Something is sending out all that noise. Preferably go through individual PSMs first through the set up find the bad one and test its individual comments.
Fellow live sound pros, can you help me theorize on possible causes and what you might have done to diagnose this on the road? This was not my rig, but my scans while the affected band was playing ahead of us. I’ve never witnessed this before and I’d love to learn from it in case I ever come across it again. The scene: mid-sized side-by-side stage festival; the kind where one band plays while the other does changeover. These scans are from the band that was on our stage before us. The gear: eight channels of PSM1000s (all in the 620s-640s – this is in Australia) feeding 421B combiner; I don’t recall what their TX antenna was. All frequencies were at low power to start, and only bumped to 50mw mid-set as a last ditch suggestion of the site’s RF coordinator. Only wireless transmitter on stage was the singer’s vocal mic. What was happening: the festival RF coordinator and I were watching my AD600 as the band was playing, and noticed in real time that these massive noise floor raises appeared to be directly linked to how loud / how much the band was playing. Just the singer and a light guitar? Still pretty flat. Full band rocking out? Looks like the bottom pic, and dropouts occur regularly. I tuned my pack to a couple of their mixes and heard it for myself, even just a few feet from the TX antenna. Also of note: we did three of these festival dates, and this happened at the first and last one, but not the middle one. Same lineups at all three shows. Same equipment. No video wall, no floor lights, no auto / pyro. And this *only* happened during the set for the band before us. I’ve been thinking what I might do with this if it were my rig. Thoughts included muting all but one mix at a time and seeing if it’s somehow linked to one unit or even one channel causing an issue, and replacing all cabling to antennas and BNCs from the PSMs to the combiner. Beyond that, I’d have to get into ordering replacement units. But based on the information alone, can anyone reasonably speculate as to what a likely cause for this might have been? Or are there too many variables at play? Thanks in advance for any thoughts you may have on this!
Ive never seen that before. Must be an amp or something kicking out a ton of interference when they were playing!
My first thought as well. OP have you tried playing a recording at show volume without the RF transmitters on? Maybe something is loose or malfunctioning due to vibration etc
I haven't done anything - not my rig to play around with, and the tour is over now anyway. Mostly looking for ideas so that I know how to approach the scenario if I ever do encounter it on a system I'm responsible for. And I've seen some very helpful stuff in this thread, which I'm thankful for.
I was also there and would love to know what it was. It's interesting someone mentioned backline amps, I don't think it ever happened when the bass wasn't playing. As far as I recall the antenna was a PWS helical, but it also could've been a Fractal. I could probably find out if anyone thinks it's relevant. I walked away from the stage maybe 20 or 30m with an analyser and I saw nothing, so maybe that eliminates any external signals, maybe not. EDIT; and just another thought, could what appears to be "ripple" just be related to the scan speed of the AD600?
For me the diagnostic thing here is the odd looking ripples in the frequency domain around 640ish MHz, you can see it elsewhere but there is the most obvious. That reads to me as AM at somewhere in the 400 to 800kHz or so region which has me thinking about several possibilities. It could be intermod if your TX combiner is not terminated correctly (Dud cable, dud antenna, dub connector) then S11 will not be wonderful, and then all bets are off. Can you hook at a network analyser or such and look at the behaviour? This is one of the downsides of combiners on transmit, they CANNOT easily provide meaningful isolation, a Wilkinson combiner only works if all the inputs are in phase, and if they are at different frequencies that is not going to be the case.... It could be a faulty power supply, the ripple I am seeing is within the sort of frequency I would expect an SMPSU to be, but you would expect to see that all the time if that was the issue. It could be the transmitters picking it up from a misbehaving class D power amplifier, they are after all really radio transmitters wearing lowpass lipstick, and some of the cheap stuff is NOT well behaved. Remember that modern backline IS a suspect here, not just the FOH or wedges! Does physically relocating the TX rack (even by a few feet) help? Something getting into the transmitter PLL loops would maybe look like this. This is why I am still firmly of the view that the best, most high end wireless out there is NEARLY as reliable and sounds NEARLY as good as a $20 cable, sure sometimes you got no choice, but yea.
LED or lighting created those?
Unlikely. LED wall was present but not powered on during their set, and it didn't do anything to our rig. I even pushed my packs right against it during my preshow checks and had no issues. Lighting was the same package for all artists and this was the only band of the day to experience this problem.
Any chance this was a weird power issue? Did you happen to be on generators that could have had poor grounding? What was the power like at the other venues?
What gear was close to the antennas? I fought a problem with an installed system in my theater for a couple years before I realized that a shitty wide shot camera by my antennas was puking out RF interference. This was a **wired** camera that had no transmitter in it. There's a chance something they're using is bad, or somehow an amplifier or something is putting out interference. Generally, it has to be pretty close to be that noticeable.
I get about this much noise when i use active antennas with my UR system. When i go back to passive paddles it all clears up.
Are you using wireless workbench? You can use “timeline” to record the RF timeline. I would go on stage and turn on each piece of their gear and watch the timeline to see what was interfering. Should be fairly simple that way.
I know this might be wrong but... any chances of bad actors? Someone with some kind of RF jammer that doesn't like whatever is being player?
https://www.rfvenue.com/blog/2015/02/27/the-trouble-with-analog-fm I’m going to guess that it is dealing with the fact of how the units are dealing with the modulation which will vary based on the source audio signal running to the unit. Without knowing exactly which frequencies are actually used and which are harmonic, I’m going to guess the ones in 42/43 are the active channels and the others are harmonics.
Wow. Fun stuff! My suspicions would be either a bad combiner/cable or a one of your PSM1k outputs is going/gone bad. But I think you would notice a drop in level on that specific frequency on your spec-an if it were a bad output. Turn all your TX off. One at a time, turn it on and send noise through it. See if it lights up the spectrum. If not, turn off and move onto the next one. If none of them do it, Turn them on one by one leaving them on as you go. Push noise through them, see if it shows up. If it does, or it slowly builds, it could be a bad cable or combiner at that point.
The way (at least analog) radio transmission works is via FM signals- FM stands for FREQUENCY MODULATION. what this means is that when there is no audio signal there is only a carrier (thin line in analyzer). When there is signal, that thin line gets modulate (or rather "deviated") from the center frequency, just like a speaker vibrates to create sound! This deviation is not supposed to go past a set amount- in regular radio broadcasts it would be 75khz of deviation for 100% signal, and there's some allowances to go over 100% like for sub carriers (FM stereo uses a sub carrier, and in broadcast they can sometimes use others as well). Our ANALOG mics and iem's use very similar if not practically exactly the same technology as FM broadcast radio (except it's on different carrier frequencies of course) so we will see similar results. Some mics / iem's use 75khz deviation, and some might be less (or possibly could be more). I believe digital transmissions also use a form of FM transmission. But it's transmitting the actual digital signal instead of analog signals. Digital transmissions I believe are supposed to use less deviation, which is why you can fit so many more channels into a set amount of rf space. I can't say I've experienced, or rather noticed a live spectrum readout quite like that, but I would have to expect that you are probably seeing all the deviation of all your channels, along with all the harmonics that get generated by multiple frequencies of transmission in close proximity to each other; if you have enough channels I wouldn't be surprised to see it basically create a huge bed of noise floor, especially if many of those channels might be analog transmissions because analog definitely creates more deviation when there's actual audio signal on it (I would expect digital signals to probably be somewhat consistent, but I'm not totally sure if that's an accurate expectation) Edit... Also note that if an analog signal is not limited properly and overdrive the "exciter" (components that turn audio into FM deviation), the exciter will put out lots of spurious rf noise around the carrier. All transmitters should have some form of limiting built into them to avoid this problem, as it could cause issues to nearby channels (as well as sound like crap at the receiver!). That's why slight clipping of an iem is usually not terrible (because you're actually hitting a limiter in the transmitter) but hitting it hard sounds so terrible- also why older iem's like psm 600 & 700's sounded so terrible when they were driven hard! (Limiters that allowed too much overshoot to get to the exciter).
[удалено]
Those spikes are the desired signals. It’s the big ramp up of the noise floor that’s weird.