At 8:33 AM -0500 4/28/08, Curt Olson wrote:
>Here's my experience; yours may vary: I first encountered this problem
>about three years ago recording in an environment that included loud
>vehicles running and vehicle doors opening and closing nearby. Later,
>using the service door to my garage as a sound source, I was able to
>reproduce it very easily at both "High Sens" and "Low Sens" settings
>(using Shure WL-183 mics).
>
>Of course, I eventually was able to turn down the input gain enough to
>make a clean recording that did not "bottom out." I transfered that
>clean recording directly into ProTools and then played it back into the
>recorder's line input. It was very easy to make the recorder "bottom
>out" in that configuration also. I inserted a WAVES Qx high-pass filter
>into the ProTools playback channel and played with different knee
>frequencies, curves and output levels. In the end I found that
>high-pass filtering with a rather standard curve and a knee set to
>about 100 Hz pretty much eliminated the problem. It seems to me that
>this "bottoming out" issue is due to a flaw somewhere in Sony's
>input/ADC path that is common to all coarse input level settings.
Raimund's chart seems to confirm that the Hi-MD pre at high gain
clips at lower levels compared to other recorders:
http://www.avisoft.com/recordertests.htm John Beale and Richard have
measured and discussed this:
http://www.wildlife-sound.org/equipment/himd/himdpklevels_meas.html
Coincidentally, in discussing the pre/adc chip Sony uses, Richard
suggests that the 20 dB difference in sensitivity between of the
Lo/Hi Sens settings is realized with feedback resistor adjustments as
Dan was describing today about the FR2-LE's "Trim" setting.
>
>(Incidentally, I've confirmed this problem on multiple Hi-MD units, a
>TCD-D7 DAT recorder and even the cute little NT-1 micro-dat.)
I see that Raimund's numbers suggest that the SONY DAT TCD-D3 is
_less_ subject to clipping than Hi-MD (-56 vs. -64 dBU).
>
>So yes, it's true that turning down the overall gain (or switching to a
>lower sensitivity setting) will reduce the low-frequency content, along
>with everything else, perhaps just enough to get below the threshold
>where the problem kicks in. The work-around I settled on for the WL-183
>mics was a Sound Professionals PIP battery box with built-in HPF. This
>permits me to safely record at more optimum levels in places where
>there might be some occasional low-end "bumps."
More clues could surface with a Lo-Sens vs Sound Professionals PIP
battery box A/B listening test, but our work-arounds probably
wouldn't change. I use the Lo Sens setting quite a bit in the city
and almost always for voice with electret lavaliere micing. Rob D.
>Curt Olson
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