I think it's time to start this project. Some EIN values can be
calculated from published specs, but many cannot be. For example, the
670/671 is -121 dBu, but to get that you need to know the mic standard
level is 1.2 mV, which is -56 dBu, then subtract the 65 dB s/n ratio to
get -121 dBu, so if you don't have both the standard level AND the s/n
you can't make that calculation. The MT2496 doesn't make it clear what
the s/n reference is, but if you use the reported max. mic level of +4.3
dBu, then the EIN is +4.3 - 100 = -95.7 dBu. If you use 1 volt as the
signal (as though the s/n were -100 dBv), then the EIN is 102.2 dBu, and
if you use 0.775 volt RMS signal (that defines a dBu standard) then the
EIN is -100 dBu. But the mic tests mentioned below doesn't support that
noisy a preamp.
The things we really need to know to make a good decision about preamps:
*EIN, equivalent input noise, in negative dBu-A (a poor way of
indicating A-weighted measurements).
*Headroom (how high a mic input signal the electronics can handle) in
positive dBu-A.
*Some idea how much gain there is in the preamp stages, and gain control
range.
For microphones:
*Self noise, in dB-A or SPL-A (this is the familiar value, but useless
in comparing to preamps).
*Maximum mic output, in dBu-A, calculated from sensitivity and max.
SPL).
*Noise floor, in dBu-A.
Then the mic-preamp combination properties can be determined, as in Rane
Note 148. The big questions are, as I see it,
(1) Can the preamp handle the full output of the microphone, and
(2) Will the preamp contribute much noise to the microphone's signal?
Beyond numbers, we can only rely on anecdotal testimony for the sound
characteristics of each combination, or build some sort of sound library
for comparison. A while back Raimond
(http://groups.yahoo.com/group/naturerecordists/message/20726) posted a
comparison between the MT2496, 671, and 722, and Rob posted recently a
MT2496, NH-900, 722 comparison. Perhaps something following those
examples.
Bruce
>From Rob Danielson:
>Wouldn't it benefit us in our decision-making about recorders/mic
>pres if we had a chart providing EIN specs for the popular recorders
>and mic preamp gain?
>
>There's been much unsatisfied discussion on this list and others
>about what the heck "Mic Signal to Noise Ratio IEC A weighted: 65dB"
>for the PMD-671 means in terms of noise performance,.. and what the
>heck the mic pre gain is for this unit.
>
>On the right test bench, one could get an accurate EIN number and
>measure the mic pre gain. Isn't such a chart something we need to
>create? Rob D.
>
>
>>
>>I've just been running over these figures this weekend to
>calculate if I
>>should get a 722 and Rode NT1-A mics (or similar) for canyon
>recording.
>>
>>Bruce Wilson KF7K
>>http://science.uvsc.edu/wilson
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