Rob Danielson wrote:
>>> At one time, there was speculation that the low PIP voltage in Hi-MD
>>> could be responsible for "bottoming-out" distortion with electret
>>> mics. Later, it was discovered that if one uses the "Lo Sens"
>>> setting when recording loud sounds that this problem went away. Loud
>>> sounds can be defined as those that require a record level of "11"
>>> or lower in the "Hi Sens" mode. Rob D.
Curt Olson wrote:
>> Welll, not exactly... Hi-MD recorders will bottom out at "Hi Sens,"
>> "Low Sens" and line in. It's about low Hz content, not overall level.
>> The only thing that makes it go away reliably is low HZ cut
>> filtering.
Rob wrote again:
> We may be experiencing a discrepancy here, Curt.
>
> Yes, sounds with lots of low-frequency content do make the problem
> more evident in Hi-Sens mode, but after Greg Evans prompted the group
> to try the "Low Sens" setting, I was not able to personally create the
> problem with using this setting on my NH900 and NH700 Hi-MD
> recorders with WM-61a, WL-183 and EM-158 electret mics. I tested
> rumbling thunder and a close-mic'd idling diesel engine. Using
> "Lo-Sens," however, does not work-around the limited max input level
> of these electret mic models (~120dB SPL max).
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.
(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.)
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."
Curt Olson
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