2
Date: Mon Aug 24, 2015 9:49 pm ((PDT))
From: Gregory O'Drobinak <>
To: "" <>=
Sent: Monday, August 24, 2015 11:19 PM
Subject: Re: [Nature Recordists] Re: EIN from Sound Devices 788
David:
How does one calculate the 'thermal noise' of air?=A0 --> I assume that it =
is a function of temperature, but does the diaphragm of the mic have anythi=
ng to do with it?
Then how does this thermal noise calculation translate into an equivalent m=
easure of dBA or or EIN for a given mic?
It's time we put some quantitative measure on this subject.How does one kno=
w if 'thermal noise' is a factor if we can't calculate or measure it?I know=
that B&K has a mic (Type 4179) with an EIN of -2.5 dBA, so the thermal noi=
se of air seems to be extremely low.
Thanks for your help and consideration in this matter.
If anyone else can step in and give some solid technical advice on this sub=
ject, please feel free to add to this discussion.
All the best,Greg
From: " [naturerecordists]" <=
oups.com>
To:
Sent: Monday, August 24, 2015 8:08 PM
Subject: [Nature Recordists] Re: EIN from Sound Devices 788
=A0 > Sound devices have not stated the Eqivalent Input Noise on the Spec=
s site from the 788.
> I asked them, and today they answered me =84looks like -126db=93. (althou=
gh they did not say how they measuered, with how much ohm and filter yes or=
no)
Emil,
I've looked up the specs and the input noise is the same on the
multi-channel version. Whatever recorder version you have, it is going to
have the same input amps.
For wildlife recording, I find mic hiss from high quality Sennheiser mics
sings through over the preamp noise and the acoustic background noise up in=
the higher kilohertz. One reason is that the HF sounds get filtered by the=
air with distance. In any case the standard "A" weighting curve doesn't
apply at the frequencies and levels we often are recording in wildlife
recording. The "A" weighting curve is (badly) based on the accepted average=
40dB hearing curve, a response which probably none of us have anyway.
Mid and low frequency noise is usually well masked in most outdoors
locations anyway, which is another reason that "A" weighting curves don't
tell you much.
What can be important is matching the mic impedance, but input circuitry
nowadays is quite forgiving. On my kit I use MKH mics with an actual
impedance of around 20 Ohms going into an actual preamp impedance of around=
|