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Mics mono/stereo (1 Viewer)

Avetarda

Active member
Spain
Hello again.
One question:
I'd like to buy a mic for to do a homemade dish. The mic is mono. For my recordings to be in stereo, would I've to buy two mics and then, to connect them to the recorder, using a 3,5 mini jack adapter?
 

Mono

Hi!
Staff member
Supporter
Europe
If you are using them with a parabolic dish the source is effectively mono, there is no stereo image. A mono mic placed at the dish focus is all you need. If you want a stereo file for some reason then you can duplicate the mono track in post processing.
 

Jon.Bryant

Active member
Hi,

I think you need to distinguish between stereo and mono (dual mono). With a stereo signal the tracks are different - loudness and time lapse - so that the recording captures and recreates the sense as to whether the sound is from the left or the right. For mono you can have a single track file, or you can have the same sound recorded to the left and right channels (dual mono), which I think is what you are thinking about. With the same recording on both channels, the bird will sound as if it is directly in front. For a parabola the focus is directly in front, so if well aimed your subject should also be directly in front. Therefore mono recording will generally be sufficient, as you are not trying to recreate the sense that the bird is to the left or right

The question then stems back to cabling and the recorder as discussed in a previous thread - i.e. does the cable split the same signal (from one mic) and feed it to both channels or does the recorder have the ability to internally route one input to both channels? If you do only have one channel recorded (on the left or right channel) it is not a big issue, as it is easy to duplicate the recording to both channels using software on your computer - I am pretty sure the the free Audacity software will do this.

To reinforce the concept of using a mono mic and making do with a recording on a single channel (left or right), the Telinga Twin Science mic, is actually an omni mic facing out and a cardiodal mic facing in. This means that this setup records two different mono tracks, that should not be played back together, and do not form a stereo pair. The set up is meant to be a highly focused and sensitive channel and a more forgiving backup channel. With this setup, you then have to select the preferred channel when editing and create a new mono recording, from whichever you select. This would be a basically be very similar to the process, if you had only recorded to one channel.

On the above basis, I would suggest one mic and look at appropriate cabling to record one signal to both channels. Alternatively just record to one channel and resolve when editing on your computer later.

I would definitely advise against thinking about stereo in a dish configuration, as I really can't see the advantage and it would be a technically challenging and probably fiddly setup to create yourself. For those that do see the advantage of a stereo parabolic setup, I would suggest saving you pocket money and relying on Telinga to provide the technical solution - they sell a stereo capsule for their parabola system, which I think works on the principle of a central baffle splitting left and right channels.
 

Avetarda

Active member
Spain
Wow! Thanks so much to you, Mono and Jon.Bryant. I buyed one mic mono. When I get the order, I'll build the dish. Thanks again!
 

Vollmeise

Well-known member
(...) For those that do see the advantage of a stereo parabolic setup, I would suggest saving you pocket money and relying on Telinga to provide the technical solution - they sell a stereo capsule for their parabola system, which I think works on the principle of a central baffle splitting left and right channels.

So maybe You should take a look at dodotronics stereo mics specially made for parabola use. They also do use a splitting baffle and a set of four high sensitive condenser mic capsules (2 at its left / two at its right hand side).

You can order them separately for DIY parabola projects or as a complete set with dish, handle and wind screen for less than a quarter of the swedish version.

I've been using the dodotronics stereo parabolic microphone myself for some time and can only recommend it.

Cheers)
 

besaide

Active member
Hello again.
One question:
I'd like to buy a mic for to do a homemade dish. The mic is mono. For my recordings to be in stereo, would I've to buy two mics and then, to connect them to the recorder, using a 3,5 mini jack adapter?

One thing is to record in mono and do it stereo in post and another one is to listen in stereo in real time.

If you have one mic, you can use only one channel to record in mono and then use audacity to copy and paste and create the second channel so you have stereo.

If you are recording in mono to the recorder and you are listening the recording in real time... you are going to listen only from one ear (Olympus LSP1)

You can use one mic and connect both channels of the plug with the same signal so you are listening the same from both ears in stereo.

This is a prototype I did when I started birding:

Stereo parabolic dish (AOM 5024L HD) + home made "battery box". It has two outputs, TRS for the recorder and TRRS for the smarthphone (birdnet)




Be able to watch the spectrogram while I am listening is something I apreciate a lot!!



Detail of the internal part:



TRS and TRRS outputs:



Detail of the system for the mic (to avoid vibrations)



With the mic



I can put this parabollic on a tripod and I can carry it as a shoulder bag.

----------------

If I made one now, it would be mono with 4 mics in parallel.
 

Mono

Hi!
Staff member
Supporter
Europe
Sorry if I'm being stupid but I don't get the point of putting a stereo mic in a parabolic reflector. A parabolic reflector has a single focal point, incoming sound is concentrated at that point. The purpose of a parabolic mic is to record from a single distance point source there is no left/right image you are trying to record. Indeed if you are using two separate microphones next to each other or in a crossed pair there is a good chance that neither of them is actually at the focus of parabola.
 

besaide

Active member
Sorry if I'm being stupid but I don't get the point of putting a stereo mic in a parabolic reflector. A parabolic reflector has a single focal point, incoming sound is concentrated at that point. The purpose of a parabolic mic is to record from a single distance point source there is no left/right image you are trying to record. Indeed if you are using two separate microphones next to each other or in a crossed pair there is a good chance that neither of them is actually at the focus of parabola.

I am not an sound expert..... all the contrary, a very beginner. I did this prototype to learn :) You are right, the best is to search the focal point and place the mic there.

When I record with this setup, in stereo, I only use one channel in audacity because both are almost the same. So if I modify it, it will be mono for sure.

I did some experiments with high pass filters, all based in the information I found here: Electret battery box

Summarising what I learned:

The circuit of the website works very well if you want to record audio. There is an option to use a high pass filter and an option to not use it, but all the time the mic is powered with around 8v.

What I did different is to use also a stronger high pass filter, change the the 100nF capacitor for 22nF/47nF so it emphasises its effect. It is not good for recording but it is good for listening in real time if you have a lot of low frecuency noise (ambient noise with cars, factories, etc. )

The option to remove the high pass filter (Eagle owls, tawny owls... Low frecuencies ), using around 800Hz high pass filter for overall recordings and using a stronger one for noisy areas only for listening is a very good setup :)

What I am using now is a completety different setup, ultralight and very portable that works very well. It has a permanent high pass filter, the mic is powered with around 8v and the mic can be moved on the axis to the desired position. Once you detect a bird, you can leave the dish tilted and aimed at the bird and walk away or hand held if it is not shy. You can also use a TRS output to record or an TRRS for birdnet, this one is my favourite so far :)
 

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Vollmeise

Well-known member
@besaide,

unfortunately it is not possible to create a stereo signal from a single or two identical mono signals.

The principle of stereo recording takes place on two microphones that record two different audio signals from a slightly offset distance. This alone creates a "spatial" sound image during playback, from which the direction of individual sound sources can be heard.

In order for a mono recording to be pleasant to listen to via stereo headphones or stereo speakers, the mono signal should of course be placed on the left and right channels during post-processing. Of course, it still remains a mono recording.
 
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Avetarda

Active member
Spain
How many centimeters should I place the mic from the base on a dish 40 cm diameter and 17 cm height? It's the typical squirrel baffle. Any recommendation to make good use of it?
I attach a pic of how I plan to do it.
 

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Mono

Hi!
Staff member
Supporter
Europe
You can use the formula as a guide but it is unlikely that the squirrel baffle is an actual parabola. It would be straightforward to experiment, have a phone running a tone generator, or even birdsong, the move the mic back and forth and look at the signal strength.
 

Avetarda

Active member
Spain
I just tried it though at home. I'll have to go out to the field and try. I move the mic back and forth and they don't seem to notice good results, or the expected results, such as not amplifying the sound. The micro is the recommended for these cases Primo 272 ... 🤷🏻‍♂️
For now, better results with ME66 y the blimp. I'll wait to test it in the open field.
 

besaide

Active member
Hi Avetarda,

I use the squirrel baffle at home for night recordings and haven't tested it in the field. The one I use more is the "umbrella", I am going to test both of them to compare :)

There is a easy test you can do putting the ME66 inward on the shaft of an umbrella, this should work pretty well. Even in the squirrel baffle.
 

besaide

Active member
I have tested my two parabolic dishes tonight. (Curtains are to prevent the neighbours from seeing that I am recording)




3 files:

1 Eagle owl with the squirrel baffle no edit (only one channel)
1 Eagle owl with the umbrella no edit (microphone below the shaft, normally I put it above) I have to test it again.
1 little owl with the squirrel baffle no edits (both channels)

Recorder: Olympus LSP1 with the "battery box" - gain level 10. Mic: AOM 5024L HD

Audio with the squirrel is around 10db higher than the umbrella with more noise. I didn't expect these results, I thought it would be the other way around, better audio level with the umbrella.

And here the audio edited and uploaded to ebird: https://ebird.org/checklist/S81265788
 

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Avetarda

Active member
Spain
Thanks for taking the time and testing. Let's see if the work leaves me for a while and I try it, the other day I did a test in the field but it was too wind to have results.
 

besaide

Active member
Tonight I have changed the position of the parabollic dishes and placed the mic of the umbrella above the shaft.

Haven't recorded any interesting bird. I am attaching a file with a sound (above umbrella, below squirrel (one channel))
 

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Vollmeise

Well-known member
besaite, I'm afraid the housing of your mics will work as a shield and and this will lead to no amplifying effect of the squirrel / umbrella at all, because sound cannot hit the microphone(s) from the back and the sides.

Maybe You should place the capsule with almost no housing right into the hotspot area of the umbrella, facing backwards. This would be possible with the help of wires that You stretch across the edge of the squirrel / umbrella.

Cheers)
 

besaide

Active member
besaite, I'm afraid the housing of your mics will work as a shield and and this will lead to no amplifying effect of the squirrel / umbrella at all, because sound cannot hit the microphone(s) from the back and the sides.

Maybe You should place the capsule with almost no housing right into the hotspot area of the umbrella, facing backwards. This would be possible with the help of wires that You stretch across the edge of the squirrel / umbrella.

Cheers)
Thanks for the advise :) I have ordered 6 mics and they are on the way. Aluminium tubes are not a good idea either.

I am going to rebuilt the "umbrella".
 

Vollmeise

Well-known member
besaide, as you'll rebuild the "umbrella", you can focus on a parabolic mic with a double-sided boundary microphone inside, using the AOM5024L.

The boundary microphone's principle itself will lead up to 6 dB of amplification, the double sided usage will allow you to get a real stereo signal.

Feel free to ask for details if necessary.

Cheers)
 
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