Something very similar was happening with the first 744's and your
detective work is very consistent with their findings. I took an
early unit to the woods and promptly cranked up the gain. The files
made by the two mkh mics had very low frequency bumps at exact
intervals-- about every 5 seconds as I recall. The NT1A's files were
fine. The source turned out ot be subtle voltage drops to the
phantom power supply circuit each time the hard drive started the
write cycle. I never learned why the mkh's were affected and not the
NT1-A's. Of course, Sound Devices was able to make a modification to
remove the audible bumps entirely which all later units have.
It never occurred to me that the periodic disc sounds with my NH-900
HiMD are write cycles because the period is so long, about 8 seconds.
Make sense, what else could it be? In quiet locations, I put it in a
leather carrying case to absorb the clicking.
In Len's critique of the M-Audio recorder's specs, he mentions the
challenge of running the 48 volt phantom supply to the mics on such a
low voltage. Some of the phantom supplies I tested with the NH-900
had less noise when operating on higher voltage. Does the MD-MS722
run on more voltage?
Sounds pretty pronounced if you're getting audible interruptions at
record level 10. But then, the bumps were always there in the same
proportion with the 744, just much harder to hear. I agree with Curt,
maybe try varying the powering demand placed on the mic pre circuit
with different mics and even an external phantom unit? Rob D.
=3D =3D =3D
At 8:56 PM -0700 8/19/05, Dan Dugan wrote:
>A few months ago my beloved Sharp MD-MT90 finally gave out, and I
>replaced it with a new recorder. They don't make them like they used
>to. The MD-MT280E has a plastic case and feels cheap. It has fewer
>buttons, and displaying remaining time requires going through a
>rather obscure menu process that I'm still not comfortable with. No
>rechargeable battery, just one AA cell.
>
>Fortunately it sounds just as good as any Sharp, but I ran into
>something new the other day. It was quite breezy where I was
>recording, and I wanted to make sure none of the wind noise
>overloaded, so I could filter it. I turned down from my usual record
>level of MIC L 17 to 12. That's 10dB down at 2dB per step. I figured
>I'd boost it back up in post. It was a quiet location.
>
>When I loaded the disc into Pro Tools and jacked it up 10 dB I got an
>unpleasant surprise. There was just audible above the mic hiss some
>clearly digital hash that would come and go periodically. From the
>timing of it I'm sure it was when the data was being written to the
>disc. (Did you know that MD recorders don't record continuously? The
>disc only spins about 1/5 of the time.)
>
>I was recording 4-channel, with an MD-MS722 doing the rear channels.
>Sound from that, using the same gain process, was fine.
>
>-Dan Dugan
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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