There are 7 messages in this issue.
Topics in this digest:
1a. Re: EIN from Sound Devices 788
From: madl74
1b. Re: EIN from Sound Devices 788
From: Gregory O'Drobinak
1c. Re: EIN from Sound Devices 788
From: emil klotzsch
1d. Re: EIN from Sound Devices 788
From: Jonas Gruska
2. Recordings from Botswana
From: Daan Hendriks
3. field laptop for hydrophone recordings?
From: Jodi Gronborg
4. SQN 5s
From: emil klotzsch
Messages
________________________________________________________________________
1a. Re: EIN from Sound Devices 788
Posted by: madl74
Date: Tue Aug 25, 2015 8:25 am ((PDT))
> David:
> How does one calculate the 'thermal noise' of air? --> I assume that it is a
> function of temperature, but does the diaphragm of the mic have anything to
> do with it?
Gregory,
The equations can be seen in;
http://www.bksv.com/doc/technicalreview1972-3.pdf
but I prefer to think about tiny ping pong balls rattling around at random.
they only stop at absolute zero K or about -273 C.
The noise level they make when rattling against a mic diaphragm goes up with
temperature and frequency, the latter at 3dB per octave, so we need to
choose a frequency band, hence the standard A-weighting and also state a
0 phon starting point which is taken at 1 KHz.
The Phon is defined as an RMS pressure of 20 microPascals. This is an
arbitrary level and most people can't hear it at 1KHz. However, as the
thermal noise rises at 3 dB per octave, keen ears can just heat a faint
hiss. I reckon I have heard it once while in my teens in an extremely quiet
place after resting for about an hour. My breathing was thunderous, my heart
thumping noisily and once my stomach and ear ringing settled down I heard a
faint high pitched hiss.
Wiki is not very helpful but SPL is discussed on:
https://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_level
If you scroll down, it gives a table of sound levels.
> Then how does this thermal noise calculation translate into an equivalent
> measure of dBA or EIN for a given mic?
Excess noise in mics is theoretically the difference between the total
output noise compared with the expected incoming thermal noise of the air.
With a diaphragm mic with an incoming wanted sound from the front, air
thermal noise is incoming on both faces of the diaphragm, giving a
theoretical limiting noise figure of +3 dB. However, this type of instrument
mic wouldn't stand up to everyday use, and the hardy MKH series of mics
compromise at around 10 dB excess noise (weighted and above 0 Phon)which is
about as good as it gets with any field mic.
Once you push up the gain in a quiet location, as I explained before, you
can hear, or see on a spectrogram, high frequency air thermal noise. This is
because you ears don't follow the Fletcher-Munson curves which no longer
apply;
https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves
David Brinicombe
Messages in this topic (12)
________________________________________________________________________
1b. Re: EIN from Sound Devices 788
Posted by: "Gregory O'Drobinak" gmo_dunes2
Date: Tue Aug 25, 2015 1:03 pm ((PDT))
David:
Thanks for the references, below!
As for the exact calculation of the thermal noise in air, I found a reference
here:http://scitation.aip.org/content/asa/journal/jasa/23/6/10.1121/1.1906831
The only issue with it is that I can't find a free copy of it (the ASA article
cost is $30.00, the cost of a whole book!), so I will try to get a copy from a
library.
However, the whole issue of microphone capsule self noise seems to be a bit
more complicated than you make it out to be, below, and is not limited by a '0
dB SPL barrier'.
The B&K Type 4179 capsule has an inherent noise floor of -5.5 dBA, which is
less than what you quote as a theoretical value for self noise. Note that the
microphone system, comprising the capsule and preamp, has an inherent noise
floor of -2.5 dBA which is due to the compensation filter in the Type 2260
preamp. The data sheet is here:http://www.bksv.com/doc/bp0389.pdf
The description of that mic capsule points out that the dominant self noise
source is generated by the resistance of the mic capsule's damping system. This
resistance is frequency dependent and generally rises to a frequency peak, then
falls off, an aspect that was explored in the reference you provided from B&K
(good paper!).
Assuming the microphone manufacturers make good, low noise internal preamps,
the final self noise of the system is mainly determined by the construction of
the mic capsule itself. So it appears that the thermal noise of air is not
really the issue. Rather, it is the electrical noise produced by the thermal
effects of the capsule's damping resistance and that of of pressure
equalization vent resistance.
This really explains why it is hard to make a low noise mic that also has good
frequency response, which is related to damping. Note also that if the thermal
noise of air was perceivable, then it would have been impossible for B&K to
make a 4179 capsule, since the acoustic pressure impinging on the diaphragm
would exceed the measured self noise of -5.5 dBA.
As for A-weighting, I heartily agree that it is not suitable for specifying mic
self noise, especially at low levels.ITU R-468 is a much better way to spec mic
self noise. However, this is once again just a general sign post for
measurement.
Everyone's ears are different, not everyone hears the same way. Probably most
of us have not had the remarkable experience that you describe regarding the
'thermal noise'. So the best solution is to try a mic out and give a good
listening.
Given all of this information, I propose that we forget about the thermal noise
of air since it confuses the issue of microphone self noise and let's
concentrate on how the manufacturer designed the capsule system. There are good
mics with low self noise such as the Sennheiser MKH series, the Audio Technica
AT4022 and the Rode NT1A.
All the best,Greg
From: " [naturerecordists]"
<>
To:
Sent: Tuesday, August 25, 2015 9:50 AM
Subject: [Nature Recordists] Re: EIN from Sound Devices 788
> David:
> How does one calculate the 'thermal noise' of air? --> I assume that it is a
> function of temperature, but does the diaphragm of the mic have anything to
> do with it?
Gregory,
The equations can be seen in;
http://www.bksv.com/doc/technicalreview1972-3.pdf
but I prefer to think about tiny ping pong balls rattling around at random.
they only stop at absolute zero K or about -273 C.
The noise level they make when rattling against a mic diaphragm goes up with
temperature and frequency, the latter at 3dB per octave, so we need to
choose a frequency band, hence the standard A-weighting and also state a
0 phon starting point which is taken at 1 KHz.
The Phon is defined as an RMS pressure of 20 microPascals. This is an
arbitrary level and most people can't hear it at 1KHz. However, as the
thermal noise rises at 3 dB per octave, keen ears can just heat a faint
hiss. I reckon I have heard it once while in my teens in an extremely quiet
place after resting for about an hour. My breathing was thunderous, my heart
thumping noisily and once my stomach and ear ringing settled down I heard a
faint high pitched hiss.
Wiki is not very helpful but SPL is discussed on:
https://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_level
If you scroll down, it gives a table of sound levels.
> Then how does this thermal noise calculation translate into an equivalent
> measure of dBA or EIN for a given mic?
Excess noise in mics is theoretically the difference between the total
output noise compared with the expected incoming thermal noise of the air.
With a diaphragm mic with an incoming wanted sound from the front, air
thermal noise is incoming on both faces of the diaphragm, giving a
theoretical limiting noise figure of +3 dB. However, this type of instrument
mic wouldn't stand up to everyday use, and the hardy MKH series of mics
compromise at around 10 dB excess noise (weighted and above 0 Phon)which is
about as good as it gets with any field mic.
Once you push up the gain in a quiet location, as I explained before, you
can hear, or see on a spectrogram, high frequency air thermal noise. This is
because you ears don't follow the Fletcher-Munson curves which no longer
apply;
https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves
David Brinicombe
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Messages in this topic (12)
________________________________________________________________________
1c. Re: EIN from Sound Devices 788
Posted by: "emil klotzsch" onomatopoetik
Date: Wed Aug 26, 2015 12:32 am ((PDT))
guys,
thanks a lot for all the answers!
thats great in this group, ask something, and learn something. very nice,
thanks!
your experiences with the 788 are more what i thought they should be:-)
sound devices answer was somewhat.. strange. they refused to answer how the
measured the EIN for the 788, by the way.
well, i will test a 788 against a 702 and a SQN5s in the future..
(by the way, i tested a zaxcom nomad against a 702. if anyone is interested in
the results, i can post them..)
Messages in this topic (12)
________________________________________________________________________
1d. Re: EIN from Sound Devices 788
Posted by: "Jonas Gruska" mrqwa
Date: Wed Aug 26, 2015 12:37 am ((PDT))
I would be interested in hearing your Zaxcom vs SD results.
BTW is measuring EIN as simple as plugging 1k ohm resistor to the XLR
pin (pin 2 and 3?) and setting the gain to maximum?
I can do that with my 702 if needed.
Regards,
Jonas
✺ ✺ ✺
http://jonasgru.sk
On 26 Aug 2015, at 9:32, emil klotzsch [naturerecordists]
wrote:
> guys,
> thanks a lot for all the answers!
> thats great in this group, ask something, and learn something. very
> nice, thanks!
>
> your experiences with the 788 are more what i thought they should
> be:-)
> sound devices answer was somewhat.. strange. they refused to answer
> how the measured the EIN for the 788, by the way.
>
> well, i will test a 788 against a 702 and a SQN5s in the future..
>
> (by the way, i tested a zaxcom nomad against a 702. if anyone is
> interested in the results, i can post them..)
Messages in this topic (12)
________________________________________________________________________
________________________________________________________________________
2. Recordings from Botswana
Posted by: "Daan Hendriks" daan_humanworkshop
Date: Tue Aug 25, 2015 1:43 pm ((PDT))
Hi all,
I've shared a few sounds online from a recent camping & road trip through
Botswana, Namibia & South Africa, if you're interested and also would like
to read about what it's like to go camping & recording in Bots then have a
read/look/listen here:
http://daanhendriks.co.uk/wildlife-nature-sound-recording/camping-and-recording-in-botswana/
I'll put a similar one up with recordings from Namibia & South Africa later
this week.
Thanks,
Daan
Messages in this topic (1)
________________________________________________________________________
________________________________________________________________________
3. field laptop for hydrophone recordings?
Posted by: "Jodi Gronborg" gronborgj
Date: Tue Aug 25, 2015 5:13 pm ((PDT))
Greetings! I am planning to buy (have grant $) a field laptop for my final
dissertation research season. It has been frustrating to get back to the
lab and finally get to look at my hard-earned recordings only to find the
charge amplifier overloaded in the midst of a sweep (thereby rendering
frequency profile lost) or not seeing what I thought I heard. This is my
final season to get all the data I need, and I can't risk it again.
1. Can I record directly onto a field lap top from a hydrophone? My
original recording set up was hydrophone to charge amplifier to line-in
(not mic-in) jack of Olympus LS11.
I am currently considering a Panasonic, either Toughbook 19 or Toughpad
FZ-G1. Only has one jack, but perhaps within the OS I can modify the
properties for the mic jack?
2. If I can't directly record for all of any of my components (underwater
anuran chorus recordings and/or frequency sweeps), at least being able to
transfer the SD card to a computer and listen and look at the file in
acoustic analysis software on site would be crucial.
Some of my sites are distant and when the frogs will show up and do their
thing is hard if not impossible to predict, so I get back to the lab and
don't have what I need I may not get another chance.
All and any advice is welcome.
Jodi Gronborg
PhD candidate, Zelick Lab
Portland State University
503.725.2401
Messages in this topic (1)
________________________________________________________________________
________________________________________________________________________
4. SQN 5s
Posted by: "emil klotzsch" onomatopoetik
Date: Wed Aug 26, 2015 12:35 am ((PDT))
hi,
i was told by a trusted source, that he was not satisfied with the SQN5s mixer,
regarding sound (not self noise), and build quality.
i would love to get some more opinion on that. anyone has something to say
about the SQN5s?
looking at the specs, it seems that the self noise is in the same ballpark as
the 7er recorders..
thanks!
emil
Messages in this topic (1)
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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