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Re: matching mic specs with recorder preamp -- thanks Rob D!

Subject: Re: matching mic specs with recorder preamp -- thanks Rob D!
From: "Philip Tyler" macmang4125
Date: Tue Apr 1, 2008 3:11 am ((PDT))
"As long as people tend to buy recorders before
starting to think about micing and mcs, I guess
we'll need to keep pursuing convincing models of
explanation."


Perhaps having a 'database' like your <17dBA or less self noise microphones=
, consideration should be given to a similar one for recorders? Raimund's d=
ata sheets on recorders and microphones goes someway towards this with his =
3 green + showing how 'good' a recorder is with a particular microphone.


Phil



----- Original Message ----
From: Rob Danielson <>
To: 
Sent: Monday, 31 March, 2008 8:37:36 PM
Subject: [Nature Recordists] Re: matching mic specs with recorder preamp --=
 thanks Rob D!

                At 7:55 AM +0000 3/31/08, Raimund Specht wrote:
>Hi Rob,
>
>It is probably quite difficult for a layman to fully understand these
>things.

Yes, it is and I appreciate you taking your time
to provide such a thorough explanation. The
ramifications are important even if one does not
understand the different measurement methods
involved.

I, for one, will stick with using dB(A)
self-noise numbers when drafting lists of mics to
study for certain applications. Sensitivity seems
to become much more of a factor with noisier,
lower-gain mic preamps. The rule of thumb of
avoiding those under 10 mV/Pa for nature
recording holds up pretty well.

Rane Notes 148 Table 3 can provide some crucial
insights about the role of pre noise. Ironically,
it might be most useful if one is trying to find
the specs for mics to use with a recorder that is
not ideally suited for nature recording.

Otherwise, after using Table 3 to "see" how
limited mic options become with noisier pres, the
simple lesson is to invest in a recorder with a
low noise mic pre.. Your pdf is another very good
graphic representation:
http://www.avisoft. com/test/ noisefloors. pdf

As long as people tend to buy recorders before
starting to think about micing and mcs, I guess
we'll need to keep pursuing convincing models of
explanation.

Thanks again,
Rob D.

>
>
>Rob D. wrote:
>
>>  It seems the intended use of Table 3
>><http://rane. com/note148. html>http://rane. com/note148. html
>>is
>>  for determining whether the noise output of a preamp is at least 10dB
>>  lower than the noise output of the mics. It creates dBu, A-weighted.
>>  equivalents for the mics and your A-weighted, EIN measurements on
>>
>><http://www.avisoft. com/recordertest s.htm>http://www.avisoft. com/recor=
dertest s.htm
>>plug in with no additional
>>  adjustment.
>
>Yes, this table is intended for comparing the absolute noise voltage
>levels of the microphones and preamplifiers.
>
>>  My question is whether it is appropriate to use Rane Table 3 to
>>  compare fully adjusted noise output between mics? When I try to do
>>  this, it seems I should interpret higher negative values as lower
>>  effective noise output, like preamp numbers. For example, a Rode
>>  NT1-A (5.5 dB(A) and 25mV/Pa) computes to -117.5 dBu and a MKH-20 (10
>>  dB(A) and 25mV/Pa) computes to -113.5 dBu (all numbers are
>>  A-weighted). Assuming all noise is equal for the moment, and 1 dB is
>>  the smallest unit of difference that one can hear, the table suggests
>>  the MKH-20 has about 4 audible increases or "steps" in noise above
>>  the noise produced by the Rode NT1-A. For this example, the Table
>>  seems to be in agreement with my experience with higher negative
>>  numbers resulting is less, cumulative noise output.
>
>Yes, this is true if you are looking at the absolute noise VOLTAGE
>levels. Because these two microphones have the same sensitivity of
>25mV/Pa, the absolute noise floor difference (expressed in dBu or =B5V)
>equals to the difference of the equivalent SPL noise levels (expressed
>in dBA). So it is important to know that the noise voltages on this
>table don't tell anything about the noise floor that you finally hear
>in your recording.
>
>>  Table 3 computed mic comparisons, however, that come out contrary to
>>  experience.
>
>Note that this does not work for microphones that have different
>sensitivities. This is the reason why one must use the dB(A)
>specifications to compare the equivalent sound pressure noise levels
>of different mics.
>
>>  Are you using Table 3 to compare noise output between mics?
>No.
>
>>  Are you
>>  saying that the Table 3 grid numbers are not really noise output
>>  equivalents between mics and pres-- that mics compute to "noise
>>  voltage floor" numbers where lower negative numbers effectively mean
>>  less noise output?
>
>Yes, but a lower negative dBu number does not always mean that the
>specific mic is less noisy! If this mic also had a lower sensitivity,
>you had to turn up the gain on your recorder to compensate for the
>lower sensitivity and this would also amplify the audible noise floor.
>
>[I'm going on your example, "The 20 mV/Pa model
>  > provides a noise voltage floor of -112 dBu. The 50 mV/Pa model
>>  produces a higher absolute noise voltage of -104 dBu. The 50 mV/Pa
>>  model could just be interpreted as a 20 mV/Pa microphone with an
>>  additional ("zero noise") 8 dB preamplifier. "] I can see how -104 dBu
>>  is -8dB hotter than -112 dBu, but I thought that Table 3 attempts to
>>  show equivalent noise output, apples and apples, for all mics and all
>>  pres.
>
>Yes, the table compares the absolute noise VOLTAGES (and not the
>equivalent sound pressure noise levels). This is necessary because the
>preamplifier noise can only be described by the absolute noise voltages.
>
>Regards,
>Raimund
>
>

--




=20=20=20=20=20=20=20=20=20=20=09=09=09=09=09=09=09=09=09=09






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