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After a dark winter with an awful weather nothing is as pleasant when migrant birds arrive to the country in the spring. Most birds arrive in April and May, and few species in Mars and June. So in mid May the air is loaded with birds song. What amazes me always is the fact that many of these birds are coming far distances from hot claimed continents like Africa and when they arrive they still have the power to fly around and sing almost 24/7 in several weeks.
It was no exception to this on May 12, 2019 when I arrived at Stafholtstungur in SW of Iceland  with my recording gear. Lot of snow was still in the mountains and the weather was cold but dry.
There are many bird species in this recording. Common Snipe, Golden Plover, Whimbrel, Common Redshank, Black Taled Godwit, White Wagtail, Winter Wren, Northern Wheatrxear, Snow Bunting, Rock Ptarmigan, Common Starling, Redwing, Great Northern Diver, Read Throated Diver, Whooper Swan, Graylag Goose and probably other species too.
This is a part of 9 hour recording I record over night with four Lewitt LCT540s microphones in IRT cross setup.   
Even though this part was recorded early morning, between 3:00 & 3:30, the recording is disturbed by human traffic in air and on ground. Wind noise which is usually difficult to avoid are audible in some moments. 
I do not strictly follow the rules about the IRT setup. I have 30cm / 90° between all capsules.
Counting clockwise normal arrangement for the channels are 1-2-3-4  to  L-R & Rs-Ls. But I pair these four channels L-R-L-R into stereo. This allows me to record 360° soundscape with four separated microphones without exactly noticing any time errors.
At the same time I also have four stereo recordings into individual directions which can be useful in some circumstances.
The problem with this „IRT stereo mix“ is that I can´t locate the direction of the sound source. But if I need that information I can always get it in the original recording file. 
In this recording Ch1 is facing to north, Ch2 to east, Ch3 to south and Ch 4 to west
This is a high gained recording. Recorder with 50dB gain, plus 24dB in post, close to be normalized (-3dB). So this is a „quiet“ recording even though it seems to be loud.. Quality open headphones are recommended while listening at low to mid level, or in speakers at low level.

(mp3 256kbps / 62Mb)
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Recorder: Sound Devices MixPre6
Mics: Lewitt LCT540S (IRT cross arrangement)
Pics: Canon EOS-M
Location: 64.673439, -21.628673
Weather: Calm to light gust, Cloudy  about 2°C 

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For a long time I have used Rode NT1a for nature recordings. It is a very good mic to capture the finest details in quiet soundscapes. But at the same time there is something missing in the sound quality, especially when it comes to low frequency and „audio depth“.
Last summer I got interest in IRT cross mic setup, so there was a perfect opportunity to invest in other microphones. There were not many mics to choose from with extra low self noise. Nevaton in Russia makes very interesting low noise & high sensitive mics. But my experience with MC50Quad was it did not capture the finest details of the silence as clearly as NT1a or MKH20. So I decided to invest in Lewitt LCT540s which I got for a acceptable nice price (See comparison)
I built a special shock mount for the LCT540s inside Rycote AE windshields (ORTF WS kit P/N:080210). That AE windshield is wider than normal WS windshield, especially made for stereo rigs so it is very good for large capsule, side address mics like LCT540s. Low handling noise is important for less rumbling wind noise and when it comes to LCT540, it is slightly better than NT1a.
Everything was ready for a field test in late Mars so I followed the silence into the country side. I was lucky with the weather, dry and calm, maybe too calm because it makes the silence too quiet for this field test. Anyway sometimes light gust gently wipes the top of trees and bushes which sounds fantastic in the headphones, moving slowly from left to right. It was much easier to feel the depth of the field with LCT540 than it has been with NT1a.
Nothing interesting was audible until in the early morning, about half hour before sunrise, when two Rock Ptarmigan started to „sing“. First in distance, but suddenly, maybe because of curiosity, they flied closer to the microphones and walked around the rig. The following recording is actually this moment.
It was recorded in IRT cross, which gives lot of opportunities in mixing. It gives me four different stereo recording in to four directions, all in NOS, plus many other versions too with different channel mix. It can be useful when looking into specific soundscape. It is for example possible to avoid traffic noise or other unexpected sounds from one or another direction.
The two first enclosed recording below have go through noise reduction process (above 3Khz). But the last one is a short peace without noise reduction, just as it comes from MixPre6, so you can hear the LCT540 self noise, which is about 2dB higher than in NT1a. It was recorded with 48dB gain and HPF at 40Hz. In post, I only normalize the gain level up to max, which rise the gain about +10dB. I did not change the EQ so audience can hear the sound quality at the low frequency. My feeling is that LCT540 have almost same low frequency quality as the MKH series & Nevaton which is very good
This is two versions of the same recording where I mix four channels differently into stereo. Counting channels 1-2-3-4 clockwise to L-R-Ls-Rs and the second one L-R-Rs-Ls (which is usually normal IRT setup).
This is a „high dynamic“ recording of silence, so I don´t recommend it played loud. It might destroy some speakers (ears too) if it is played too loud without attention.
Good monitor headphones are recommended or quality open headphones while listening at low to medium level.

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Recording L-R-Ls-Rs
(mp3 256Kbps / 35,6Mb)

Recording L-R-Rs-Ls
(mp3 256kbps / 35,6Mb)

Short version of recording L-R-Ls-Rs without NR
(mp3 256kbps / 7,4Mb

Recorder: Sound devices MixPre6
Mics. Lewitt LCT540s (IRT cross setup) Running on 70m Sommer Mercator CAT7 S/STP cable
Pix: Canon EOS M50
Weather: Calm, dry, between -2 to +4°C, about 7:30 o´clock

Location: 64°40’23.7″N 21°37’43.7″W

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