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Re: Hi-MD Input Clipping (was Sony HiMD questions

Subject: Re: Hi-MD Input Clipping (was Sony HiMD questions
From: "stoatwizard" stoatwizard
Date: Thu Jul 13, 2006 3:11 am (PDT)

> with Panasonic WM61A's, I found that the Low Sensitivity setting
> prevent distortion. (I'd never tested it because I assumed it was a
> pad). Could there be unique, insufficient power PIP problem with
> mics that makes the Sony's clipping vulnerability at High Sen much
> more pronounced?

This is more that there is insufficient drive from the onboard PIP
to adequately supply the mic - it is the mic that is starved of
current that is the source of clipping, because the FET has
insufficient VDS to achieve the full drain current that would
normally correspond to the mic element Vgs.

Your thunderstorm experience isn't too contrary to the Hi-MD clip
level measurement

A NH700 on Hi clips at -31dBu @ 1kHz (the clip level is not
particularly frequency sensitive). A Sennheiser MKH40 kicks out 25mV
at 1PA (=3D94dBSPL @ 1kHz). Conveniently 25mV corresponds to -30dBu
which is about the clip level on Hi-Sens. That is a sound level
equivalent to a jack-hammer 2m away which is a pretty
loud noise!

I've recorded numerous thunderstorms, wood chopping,
> ice cracks etc with condenser mics>Rolls-> without the
> distortion. An A/B comparison of with and without your battery box
> could provide clues.

I'll have a look at trying an acoustic measurement on the mics wtih
PiP and without, though this is hard to do repeatably. I feel that
the biggest problem HiMD users have is their use of PiP mics without
adequate drive. Concert bootleggers have long known about the value
of using battery boxes, as they are dealing with rock concert SPLs.

This may be peculiar to first-gen HiMD - I've just measured the open
circuit mic voltage of my ancient 1997 Kenwood DMC-G7R which is a
more healthy 5V open-circuit, biasing the same OKMII mics up to a
healthy 1.9V on PiP, which is within spec for normal ECM inserts
(Vmin=3D1.5V for the Rapid 35-1090 inserts, for instance). Basically
the PiP on the NH700 is unfit for purpose for any ECM that draws more
than 0.2mA at a capsule voltage of 1V - and I reckon that most ECMs
people use want a little bit more than that!

I would suspect insufficient PiP powering for your lute recording. I
wouldn't expect a lute to be louder than a jackhammer at 2m. Digikey
say the WM61A has a sensitivity of -35dB, so at the jackhammer level
of 1PA it would be putting out of the order of -37dBu, so clipping
shouldn't have been an issue on Hi, unless you were close-miking it.
However, the WM61A does draw 0.5mA and wants 2V across it. It just
wouldn't be able to get enough current from the PiP on my NH700!

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