problems with wireless recording

[Nana Hesler]

Hi all,

I had problems recording blue petrels on the Kerguelen Islands with a wireless mic system and I was wondering whether anybody here has ever experienced something alike or may even know what could have happened.

Obviously my equipment produced an internal noise which is not very strong and not permanently present, but still annoying. The noise is something like an amplitude modulated white noise, like a very regular and constant pulse. Examples are below (you have to turn the volume up since it is a silent moment of the recording).

I used a Tascam DR-680 recorder and dpa 4060 lo sense mini microphones connected to Sennheiser ew 112 wireless transmitter-receiver sets.

From swapping channels and sets of microphone/transmitter-receiver, the noise seems to come from the transmitter-receiver set or microphone (cannot really imagine it came from the mic though). It was however not always there and sometimes stopped completely when I changed batteries in the transmitter-receiver set, although battery state was still indicated as almost full (two out of three bars). Anyway, batteries tended to screw up everything all the time, probably because of the cold weather (not below 0 degree celsius though).

I wonder whether this could be a problem with the radio transmission? Does anybody have any idea? any help would be highly appreciated!

cheers,

Nana

[Jez riley French]

Hi,

there are a couple of potential reasons for this. Firstly I recently discovered that the way some pro-sumer recorders are set up doesn't always work that well with DPA 4060's. This is down to the balancing (or not) of the input transformers on the recorder & the unbalanced nature of the mics. There's no way round this at present other than to put the DPA's through a separate unit to correct the balancing issues. Using them with the wireless sets might have introduced the noise between these various interfaces.

secondly, & this is on a much wider point, there are now such a lot of issues with wireless recording 'in the field' - hence the reason its usually only a last resort method. Various signals entering the channels & the fact that much of the support networks for the wireless channels are no longer maintained or are subject to various 'preparing for turn off' restrictions.

That said, i'd say the first possible issue could be whats going on here.

[Nana Hesler]

Hi Jez, thanks a lot for your quick reply! There are two things I should maybe have specified:

Firstly, I had three sets of mic/transmitter-receiver which I used synchronously on three channels of the recorder. One of the mics was close to the calling bird in its breeding burrow, the second was at the burrow entrance and the third in one meter distance outside the burrow. (I want to compare the three recordings at the end). I used a much higher recording level (sensitivity) on the channel outside, as the signal was obviously much weaker outside.
I swapped the three sets over the recorder channels and the problem occurred always with the same mic/transmitter-receiver set. It was however only obvious when I used it with a high sensitivity at the recorder.
Given that, I would be surprised if it was an issue of the components, since they were the same in all three sets of mic/transmitter-receiver.

Secondly, my field was on the Kerguelen islands - in the middle of nowhere. There is nothing, no mobile phone, no electricity, only water, some islands and birds. However, there is a radio used for communication at the research station. I probably should find out what frequency they used to make sure that my frequency was not in that range.

Best,
Nana

ps: Although using this complicated equipment I am obviously not a technique expert neither a native english speaker, I hope I make myself understandable.

[Jez riley French]

Hi,

interesting. I'm doing some research on these issues between pro-sumer recorders & the DPA's (I should point out that it appears to be down to some recorder manufacturers not working out how to make their machines as compatible as others, rather than something that DPA are doing of course) & what i'm finding is that even with the same mics, same recorders there are some that have the issues & some that don't. Various folks (inc. at DPA) are looking into this. However, if its just happening on one set, which I assume works fine normally - yes ?, then it must be something to do with either a faulty unit or interference. Try these suggestions:

1) does the same thing happen if you take one good set out of your set up (ie. so you work with just two including the faulty one)

2) does the noise fluctuate when moved closer to the different components or when angled in different ways in the air

3) if you have the right connectors, try checking the 'faulty' mic directly into the recorder

4) & as you say, check the frequencies being used.

What I will say though is that even in very remote places, with no apparent radio or other transmissions, wireless systems still have issues with interference from all kinds of things. It can be the various bits of kit clashing, it can be long range radar or sonar, it can be static energy - lots of different things. Broadcast still uses wireless systems a fair bit but there its when the signal is going to be cleaned up, compressed, filtered etc etc. so any 'problems' can be sorted in post. It seems to me, & this will get even more the case when the licenses for wireless channels run out at the end of this year in most places, that using wireless technology in a more creative way can be interesting. So, playing with the problems, the interference. Of course, this isn't ideal for a project like yours where you're recording a natural environment (though, if it turns out the problem is interference then that too is part of that environment now).

[Nana Hesler]

Hi again,
and thanks again. I will try all of your suggestions. The equipment just arrived back to Europe (France), so I can see if it happens here again which it did not when I tried it before leaving, but if it is due to the surroundings it should not happen here anyway.

And it is nice to see that there are people out there who find my problems interesting, if you were interested in battery-and-low-temperature problems too, I could tell you many more stories.

[Jez riley French]

ha ! yes, problems are best described as 'interesting' as it means we are trying to be positive & learn from them - rather than just mentioning the fact that they are frustrating !

hope you get it sorted.