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NocMig Recordings - Why Shotguns or Parabola Mics (2 Viewers)

Jon.Bryant

Active member
Probably overthinking this, but why do people favour shotguns or parabolas for NocMig recordings? Does anyone have evidence of what mics work best.

To me the problem with a shotgun, is that it effectively filters out sound off axis and this is most efficient for higher frequencies, which is generally what I want to record. As an example the Sennheiser ME66 would curtail a 4khz sound (say a Redwing) 45 degree off axis by around 2.5db (i.e. almost halving the signal strength. I don't have the ME66, but the longer shotgun (the ME 67), which is even more directional and would further curtail off axis recordings.

Parabolas I think are even worse. I remember reading that parabolas work best within a cone of 15 degrees, but some data sheets show a much narrower focus that that. Even at 15 degrees, it would mean that at an altitude of 500m you are looking at a circle of space with a diameter of only 130m Using a parabola would seem to be lowering the odds that a/ a bird will fly through this cone of space and then b/ happen to call.

Some parabola mics (i.e. the Telinga Twin Science) have two mics, one of which is cardiodal and the other omini directional. Is anyone using this type of kit and if so which mic is picking up the most sounds? - i.e. the omni with the low boost but which is less directional, or the cardiodal, which should have significant boost, but be highly directional.

I presume that if a wide Cardiodal or Omni mic is the best option for NocMig recordings, then the problem is finding a mic with good sensitivity. I imagine that wide angle mics are generally not designed with high sensitivity for picking up distant sounds.

I am going to try the Wildlife Acoustics Recorder SM4, which has reasonably sensitive Omni mics and you can add a fair amount of preamp gain. I will also attach an external mic to the recorder in a homemade parabola housing - hopefully I will get a right channel wide angle recording and a left channel boosted recording of things directly overhead. Has anyone tried the SM4 for this NocMig recordings and was it successful?
 

wimvdam

Well-known member
I think it depends on what you are aiming for with your NocMig/NFC recordings. If you want to record as many calls as possible, then, yes, the narrow focus of a shotgun or a parabola would be counterproductive. But, if your goal is to try to ID the calls using their spectrogram, then those setups make a lot of sense. When I started making night recordings with a basic setup I was pleasantly surprised by how many calls I managed to detect. Unfortunately it was very hard to ID them because of the ambient noise and the weakness of the calls themselves. I now use a ME66 and the results are much better and now I have a fighting chance to figure out what species I had. It's still a struggle though so now I'm contemplating shielding my shotgun mic with a large bin. If I had the money I would definitely switch to a parabola to get even cleaner results.

Wim
Solvang, CA

PS: Identifying calls is very time consuming, so I consider a lower hit rate a blessing in disguise.
 

Jon.Bryant

Active member
As a follow up to my initial post, I set up the Wildlife Acoustics SM4 with an external mic housed in a dish. When testing this setup with a 5 Khz signal, I was amazed at just how narrow the focus of the dish is! The problem is that my recording area does not have an abundance of migrants, so I have failed to get any recordings that were picked up by parabola, but were much weaker on the other omni mic that was not housed in a dish. I am not sure if this means that the benefit of the parabola against a reasonably sensitive omni is very low, or if I just need a greater sample size for the test.

I have now tried switching to having an omni mic mounted on the roof, without the parabola, and am reasonably happy with the results, as there are a reasonable amount of good and identifiable signals.

In summary the omni on the Wildlife Acoustics SM4 seems good enough for the job - although a possible downside of using a omni mic is that terrestrial sounds are also quite loud - the local Robins seem to like singing from around 3am, then there are the foxes and Tawny Owls calling through the night. A directional mic would obviously filter out (reduce the signal strength) of some of this off-axis clutter. That said, it is still fairly easy to spot migrant calls in a sonogram amidst the Robin song.

I will retest the dish against the omni setup when I am next staying at a place with more migration activity. With this in mind does anyone know whether there is a preferred direction to set a parabola for NocMigging? Something says to me that if i set it straight upwards, I will get recordings of migrants at higher altitude, but the target will quickly pass across the focus (and may not call in the process!). If however, I was to point the parabola more towards the horizon in the direction of where birds are like to be coming from, then I may get a longer sequence of calls as the bird approaches, with the bird in the parabola focus for longer.

If there is no obvious answer to the question on parabola direction, I will add it a as another variable to future tests.

Regards

Jon Bryant
 

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