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Mobile batting (3 Viewers)
- Thread starter HermitIbis
- Start date
kbps vs kHz
The KHz values refer to wav/pcm recording format, which I prefer compared to the highly compressed mp3 recordings which are referred to in kbps. If you are not absolutely limited by space go for the kHz uncompressed files.
Harry J
The KHz values refer to wav/pcm recording format, which I prefer compared to the highly compressed mp3 recordings which are referred to in kbps. If you are not absolutely limited by space go for the kHz uncompressed files.
Harry J
Yes, I do allways use .wav files using 16 KHz sampling rate, that will allow recordings in Time Expansion up to half that value: 8 KHz, which correspond to 80KHz bat calls. As my device can only record bellow 60KHz, there is no need to use higher sampling rates.
60KHz line
HermitIbis and others,
>Since the micro trio is my first detector, I have no comparison.
>But it may be a major bug that the device mirrors signals along
>a virtual 60 kHz line. Thus a strong 40 kHz call also appears as
>a "ghost call" at 80 kHz.
Sorry for jumping in late at this discussion.
Just a comment to this 60KHz line. It is not really a bug. It is due to the sampling. Looking at the technical information and what ori76 mentioned in the previous post, the sampling in the TE mode is 120KHz. This means that the highest sounds that you can sample are 60 KHz. So if you sample at a higher rate everything below that line will be mirrored above the line. This mirroring is called aliasing. If your mic happens to be such that its sensitivity continues to even higher frequencies than half of your highest frequency, then the opposite can happen, i.e a sound at a higher frequency can be mirrored below the aliasing frequency.
Regards
Harry J
HermitIbis and others,
>Since the micro trio is my first detector, I have no comparison.
>But it may be a major bug that the device mirrors signals along
>a virtual 60 kHz line. Thus a strong 40 kHz call also appears as
>a "ghost call" at 80 kHz.
Sorry for jumping in late at this discussion.
Just a comment to this 60KHz line. It is not really a bug. It is due to the sampling. Looking at the technical information and what ori76 mentioned in the previous post, the sampling in the TE mode is 120KHz. This means that the highest sounds that you can sample are 60 KHz. So if you sample at a higher rate everything below that line will be mirrored above the line. This mirroring is called aliasing. If your mic happens to be such that its sensitivity continues to even higher frequencies than half of your highest frequency, then the opposite can happen, i.e a sound at a higher frequency can be mirrored below the aliasing frequency.
Regards
Harry J
HermitIbis
Well-known member
Harry, many thanks for your explanation about "aliasing". One thing less to worry about, and I can focus on the key problem that many files show no bat at all. It is unlikely that I'll meet a Horseshoe (the nearest colony of ~100 Greater Horseshoes seems to live in Northern Bavaria), but if it happens, I doubt whether a mirror signal would appear. The manual of the Micro Trio says that the FD mode covers 18-80 kHz, "stronger signals" up to 130 kHz. For the TE mode, it gives the following: "bandwidth 0-60 kHz; internal recording 120 kHz sample rate 8 Bit". - Presently I am struggling with the Myotis species, so I'll leave the Horseshoe problem for another day.
The MP330 can store 8 GByte of data, but it offers only three modes "low, medium, high" for the line-in recordings. Checking the resulting audio files with the free software "xrecode II", I find that the setting "high" in the MP330 produces files with "sampling rate 32000, bit rate 256 Kbps/CBR, 4 Bits per sample". A setting "medium" creates files "sample rate 16000, bit rate 128 Kbps/CBR".
Personally, I am satisfied with using TE --> MP330 (medium, volume 3) --> Audacity --> BatExplorer. I don't know why, but "high quality" in MP 330 is no improvement, rather the opposite. I guess better recorders are able to work with uncompressed files, but then I'd have to struggle with hundreds of new options to vary the settings... not a pleasant thought for a non-techie.
The MP330 can store 8 GByte of data, but it offers only three modes "low, medium, high" for the line-in recordings. Checking the resulting audio files with the free software "xrecode II", I find that the setting "high" in the MP330 produces files with "sampling rate 32000, bit rate 256 Kbps/CBR, 4 Bits per sample". A setting "medium" creates files "sample rate 16000, bit rate 128 Kbps/CBR".
Personally, I am satisfied with using TE --> MP330 (medium, volume 3) --> Audacity --> BatExplorer. I don't know why, but "high quality" in MP 330 is no improvement, rather the opposite. I guess better recorders are able to work with uncompressed files, but then I'd have to struggle with hundreds of new options to vary the settings... not a pleasant thought for a non-techie.
HermitIbis
Well-known member
Kuhl's pipistrelle or not
Here is the 34 kHz bat already mentioned in reply #92. The single recording was made on September 20. I tend to believe that it is Kuhl's pipistrelle, but doubts remain. P. kuhlii, known to live in Baden-Württemberg (if not here in Pforzheim), is the most probable option for the region, as studies have shown a trend for the species to spread to the North. The alternative is Savi's pipistrelle (H. savii). According to Dietz & Kiefer (2014) H. savii can vagabond around in autumn and has been seen as far North as in Northern Germany. Actually, the measured data for the call would fit perfectly to Savi's pipistrelle, but after checking sample files for the two species I see more similarities in the shape of the calls, the variety and the rhythm to P. kuhlii. Of course I may be wrong.
Older sources had put the lowest peak frequencies for P. kuhlii at 35 or even 36 kHz, but Dietz & Kiefer (2014) give 34-39 kHz for P. kuhlii in open habitat, and 35-40 kHz for P. nathusii. The lowest of the calls in my recording peaks a bit below 34.5 kHz. - In the last weeks I recorded hundreds of Nathusius' calls, they can indeed go down to 35 kHz, but this occurred only in situations when more than one Nathusius' were present at the place. - Anyway, it is a difficult identification, or rather a guess.
Here is the 34 kHz bat already mentioned in reply #92. The single recording was made on September 20. I tend to believe that it is Kuhl's pipistrelle, but doubts remain. P. kuhlii, known to live in Baden-Württemberg (if not here in Pforzheim), is the most probable option for the region, as studies have shown a trend for the species to spread to the North. The alternative is Savi's pipistrelle (H. savii). According to Dietz & Kiefer (2014) H. savii can vagabond around in autumn and has been seen as far North as in Northern Germany. Actually, the measured data for the call would fit perfectly to Savi's pipistrelle, but after checking sample files for the two species I see more similarities in the shape of the calls, the variety and the rhythm to P. kuhlii. Of course I may be wrong.
Older sources had put the lowest peak frequencies for P. kuhlii at 35 or even 36 kHz, but Dietz & Kiefer (2014) give 34-39 kHz for P. kuhlii in open habitat, and 35-40 kHz for P. nathusii. The lowest of the calls in my recording peaks a bit below 34.5 kHz. - In the last weeks I recorded hundreds of Nathusius' calls, they can indeed go down to 35 kHz, but this occurred only in situations when more than one Nathusius' were present at the place. - Anyway, it is a difficult identification, or rather a guess.
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HermitIbis
Well-known member
What do you mean with "real time"? Whether I saw it during the recording or noticed that the sound was unusual? The answer is no on both counts. It was already later on that evening, the bat appeared on the scene 50 minutes after I had met the first Noctule. So it was dark, and my flashlight and/or reflexes are too bad to see much of bats in the dark. But still good enough to press the TE button when I heard that a bat was approaching. Only back at the PC I saw these 34 kHz calls. So I can say that this file was recorded in the park, 100 m away from the Enz, with the bat flying along the edge of a line of trees, bordering to a small forest. That's all.
Edit: Looking at the neighbouring files, there are Common pipistrelles and Nathusius' pipistrelles. For example the file recorded immediately before the "Kuhl's" has signals at 46 kHz and 38 kHz, the file immediately afterwards has signals at 46 kHz and something around 36/37 kHz which should be Nathusius' pipistrelle again. I was walking along this line of trees, and every 30-45 seconds or so there was a bat coming along. Quite the typical bat activity in this park.
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HermitIbis
Well-known member
No, the Micro Trio puts out only one signal: either the TE or the FD signal, you cannot record both at the same time. I know that your Pettersson detector is different, with both signals recordable simultaneously.
I am used to record TE only. It is a stereo signal, a bit of a waste. The BatExplorer requires just mono.
I am used to record TE only. It is a stereo signal, a bit of a waste. The BatExplorer requires just mono.
HermitIbis
Well-known member
Hmm... I think I can exclude Barbastelle. I've just listened to the sample file for the species in BatExplorer, and the sound not only looks different in the spectrogram, it also sounds different - like a whole orchestra.
More information would help, here I really wish I had more than these 0.9 seconds.
More information would help, here I really wish I had more than these 0.9 seconds.
HermitIbis
Well-known member
Common pipistrelle, feeding buzz
My two attempts to detect bats in Pforzheim's forests have failed, more or less. The first time was a rainy evening - I knew that it means reduced bat activity, but it was even worse, as rain creates ultrasound noise. A new lesson learned. Yesterday I tried again, in theory it was a perfect night. However, the number of bats was just a fraction of what flies close to the river, mostly Noctules and Common pipistrelles. The place was mentioned in FF2, with caverns where bats are known to hibernate (incl. Greater Mouse-eared bat, Bechstein's bat, Natterer's bat, Whiskered bat, Brown Long-eared), plus many bat-boxes. But that didn't work. Next time I'll visit the small lake in the midst of the forest, which should be a relevant feeding ground.
The recording of a feeding buzz of a Common pipistrelle is too noisy to be good (this 11-32 kHz noise came from a car, I believe), but I'll show it nevertheless. It would be interesting to know whether top-notch equipment is able to filter and reduce non-bat sound like the irritating noise in this example. But I guess we have to live with it. Even deep in the wilderness of Pforzheim's forests, the next ultrasound-emitting street is never far away.
My two attempts to detect bats in Pforzheim's forests have failed, more or less. The first time was a rainy evening - I knew that it means reduced bat activity, but it was even worse, as rain creates ultrasound noise. A new lesson learned. Yesterday I tried again, in theory it was a perfect night. However, the number of bats was just a fraction of what flies close to the river, mostly Noctules and Common pipistrelles. The place was mentioned in FF2, with caverns where bats are known to hibernate (incl. Greater Mouse-eared bat, Bechstein's bat, Natterer's bat, Whiskered bat, Brown Long-eared), plus many bat-boxes. But that didn't work. Next time I'll visit the small lake in the midst of the forest, which should be a relevant feeding ground.
The recording of a feeding buzz of a Common pipistrelle is too noisy to be good (this 11-32 kHz noise came from a car, I believe), but I'll show it nevertheless. It would be interesting to know whether top-notch equipment is able to filter and reduce non-bat sound like the irritating noise in this example. But I guess we have to live with it. Even deep in the wilderness of Pforzheim's forests, the next ultrasound-emitting street is never far away.
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HermitIbis
Well-known member
Full Nathusius' pipistrelle social call
To be fair, my walk on Sunday was not a complete disaster. Attached is a much better version of the typical social call of a Nathusius's pipistrelle. All three main elements are visible in the new recording: the main element "a" with four or five components (in the terminology of the recent UK book on social calls), then the vertical element "b" and finally the element "c" in a higher frequency area.
Dietz and Kiefer (2014) say that the three species Noctule, Lesser Noctule and Nathusius' pipistrelle are known to migrate along rivers in autumn. This explains why I am meeting so many of the latter.
To be fair, my walk on Sunday was not a complete disaster. Attached is a much better version of the typical social call of a Nathusius's pipistrelle. All three main elements are visible in the new recording: the main element "a" with four or five components (in the terminology of the recent UK book on social calls), then the vertical element "b" and finally the element "c" in a higher frequency area.
Dietz and Kiefer (2014) say that the three species Noctule, Lesser Noctule and Nathusius' pipistrelle are known to migrate along rivers in autumn. This explains why I am meeting so many of the latter.
Attachments
HermitIbis
Well-known member
Brown long-eared bat, social calls
For more than two weeks I regarded my walk on a rainy October 10 as a failure and left dozens of audio files unchecked. The first 100 files or so had contained nothing of interest, so why bother? Only now did I study the remaining files and was pleasantly surprised. I detected four recordings of what I believe are social calls of the Brown long-eared bat, a new species in my collection. These four files do not show echolocation calls, just the social calls. The former are very quiet, this may explain why they are missing. (*)
How can I be sure about the identification? That's the easy part! The British reference work Social Calls... offers an example on p. 134, above, plus additional text on p. 135, which is pretty close to the file which I'll give below.
Source: Middleton, N., Froud, A. and French, K. (2014): Social Calls of the Bats of Britain and Ireland. Exeter: Pelagic Publishing.
(*) Dietz + Kiefer (2014), p. 108f., lists the Brown long-eared as one of the quietest European bats. In free flight (i. e. in open area) "detectable" with a bat detector from a distance of 10 m at best, but if the bat is hunting in the forest, the detector will "catch" the bat sometimes only in a distance of 2-3 m.
For more than two weeks I regarded my walk on a rainy October 10 as a failure and left dozens of audio files unchecked. The first 100 files or so had contained nothing of interest, so why bother? Only now did I study the remaining files and was pleasantly surprised. I detected four recordings of what I believe are social calls of the Brown long-eared bat, a new species in my collection. These four files do not show echolocation calls, just the social calls. The former are very quiet, this may explain why they are missing. (*)
How can I be sure about the identification? That's the easy part! The British reference work Social Calls... offers an example on p. 134, above, plus additional text on p. 135, which is pretty close to the file which I'll give below.
Source: Middleton, N., Froud, A. and French, K. (2014): Social Calls of the Bats of Britain and Ireland. Exeter: Pelagic Publishing.
(*) Dietz + Kiefer (2014), p. 108f., lists the Brown long-eared as one of the quietest European bats. In free flight (i. e. in open area) "detectable" with a bat detector from a distance of 10 m at best, but if the bat is hunting in the forest, the detector will "catch" the bat sometimes only in a distance of 2-3 m.
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HermitIbis
Well-known member
Unidentified flying object
It must be a bat, but so far I have no idea about the species. The known "aliasing effect" explained by HarryJ in reply #104 probably means that parts of the signal above 60 kHz can be ignored, but that doesn't help me to identify the animal. - The M500 microphone has an "anti-aliasing filter: 8th order", as Pettersson's site informs potential customers. IDying this bat would be a breeze with such a filter, I guess.
It must be a bat, but so far I have no idea about the species. The known "aliasing effect" explained by HarryJ in reply #104 probably means that parts of the signal above 60 kHz can be ignored, but that doesn't help me to identify the animal. - The M500 microphone has an "anti-aliasing filter: 8th order", as Pettersson's site informs potential customers. IDying this bat would be a breeze with such a filter, I guess.
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Yes it aliasing. If you read carefully the M500 mic specs it tells you that it can sample up to 500KHz, that means 250KHz in sound frequencies, and that the mic has an antialiasing filter "8th order, 190KHz". The 190 kHz is important. This means that this is the practical limit for the mic. If you are recording sounds well below that limit (eg. around 60kHz), then your low sampling rate will be causing the aliasing. As the mic is sensitive well above the Nyquist frequency, you can see a suggestion that your sound could have a form FM +QCF. Check your file with audacity, FFT length 128, and look at the strong sound at sec 3.00, and note how your sound looks like. Imagine a Pippip or Pippyg/Minsch call when it goes from open environment (QCF -like call) into a cluttered environment (=> FM call), and mirror it around the 60kHz line. That's when you can get something like this. There are cases where it is difficult to tell whether the echo call is from Pippip and Pippyg. No need to ID every call.
Regards
Harry J
HermitIbis
Well-known member
Harry, I am very grateful for your help. And your last sentence is surely true:
From my 2,000+ bat call files only one was a Soprano pipistrelle (Pippyg), so another sighting of the species would only be welcome. But if this file remains a puzzle, no problem. It's basically like birding: an unidentified bird is the best encouragement to re-read the reference works for your next field trip.
It seems plausible that it is some Pipistrelle. Actually, the recording was made in a little uphill park, diameter ~200 m, green island in a sea of houses. The only visit to this place (when I didn't have time for a longer walk) resulted in 19 recordings of bat calls: 18 Common pipistrelles plus "The Puzzle".
This is a bit over my head, sorry. I try to wrap my mind around it, but not too successfully. Looking in Audacity, I can change the FFT window setting from 256 (default) to 128, OK. Then I can zoom in at sec 3.00 and study the strong pulse. But all I see in zoom view are some sine waves.
I'd much prefer to "get it" in BatExplorer. I understand that aliasing distorts the picture, in particular that we must ignore what happens above 60 kHz. And perhaps finer details get lost, like the inverted "j" shape of a pip call. However, my problems go deeper: shouldn't peak frequency still be a strong hint for a possible identification? What I see here in BatExplorer (you can open the file in BE and check yourself) is a sequence of ten calls. Some are weak and not very informative, but still it appears to me that all the sound comes from one single bat. (see picture 1)
If we assume, for a moment, that there are two bats: then the odd signals 1, 3 and so on could come from a Soprano pipistrelle. The signals 2, 4 ... would still be VERY high for a Common pip, at 52.5 kHz. (see picture 2)
The end of the sequence is shown in picture 3. Here we have the last call (#10 in the overview) peaking at 49 kHz. Another difference to normal Pipistrelle echolocation calls is the observation that the strong calls 2, 4, ... all peak at the middle of the call, not close to the end, as in the usual inverted j shape.
So this recording is hard to explain. Maybe a rare social call or something?
From my 2,000+ bat call files only one was a Soprano pipistrelle (Pippyg), so another sighting of the species would only be welcome. But if this file remains a puzzle, no problem. It's basically like birding: an unidentified bird is the best encouragement to re-read the reference works for your next field trip.
It seems plausible that it is some Pipistrelle. Actually, the recording was made in a little uphill park, diameter ~200 m, green island in a sea of houses. The only visit to this place (when I didn't have time for a longer walk) resulted in 19 recordings of bat calls: 18 Common pipistrelles plus "The Puzzle".
This is a bit over my head, sorry. I try to wrap my mind around it, but not too successfully. Looking in Audacity, I can change the FFT window setting from 256 (default) to 128, OK. Then I can zoom in at sec 3.00 and study the strong pulse. But all I see in zoom view are some sine waves.
I'd much prefer to "get it" in BatExplorer. I understand that aliasing distorts the picture, in particular that we must ignore what happens above 60 kHz. And perhaps finer details get lost, like the inverted "j" shape of a pip call. However, my problems go deeper: shouldn't peak frequency still be a strong hint for a possible identification? What I see here in BatExplorer (you can open the file in BE and check yourself) is a sequence of ten calls. Some are weak and not very informative, but still it appears to me that all the sound comes from one single bat. (see picture 1)
If we assume, for a moment, that there are two bats: then the odd signals 1, 3 and so on could come from a Soprano pipistrelle. The signals 2, 4 ... would still be VERY high for a Common pip, at 52.5 kHz. (see picture 2)
The end of the sequence is shown in picture 3. Here we have the last call (#10 in the overview) peaking at 49 kHz. Another difference to normal Pipistrelle echolocation calls is the observation that the strong calls 2, 4, ... all peak at the middle of the call, not close to the end, as in the usual inverted j shape.
So this recording is hard to explain. Maybe a rare social call or something?
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