It could be something in the mic pre or even the phantom circuit. As
you have initiated, testing the 670 with different mics with and
without the Rolls in different locations should help pin down the
source. The solution, however, might not be easy to find. With
low-level sounds and high gain, we're asking the gear to perform
flawlessly at its limits and then amplifying the results to a high
degree. The awareness that recordings usually have small quirks to
obvious inaccuracies has encouraged me to learn to use filtering to
help make the sound coming from the speaker better resemble what I
heard in the field. EQ is often over-done but done right, the
difference it can make is very exciting in my opinion. I hire Peet
for everything above 10K (the loss settled in over the last year,..)
I noticed in the spectral graph on the movie that the Rolls->HiMD pre
did not pass the 13KHz environmental whine as well as the 722 or MP2
and that the high end response above 8K was lower in general with the
HIMD pre. Rob D.
At 7:59 PM +0000 1/9/06, John Hartog wrote:
>When I look at spectrograms of recordings I made using NT1-A's with a
>PMD-670, I notice a narrow band about 200Hz wide between 16K and 21K.
>I'm pretty sure it's from the recorder not the mics because it is
>always stronger in the left channel. The band drifts over time, for
>instance it might start out at 16K and over an hour or so it gradually
>rises to 19K. My ears cannot hear it but frequency analysis shows a
>5dB spike. The problem seems to disappear using the NT1-A's with a
>Rolls PB224 and my new MZ-RH10, though I haven't had much time to test
>that thoroughly.
>
>Relating this to nature recording:
>Does a band like that compromise the audible quality of my recordings?
>Should I just leave it or try to filter it out?
>
>-John Hartog
>
>
>
>--- In Rob Danielson <> wrote:
>>
>> Lucky for you that 13K stands out so audibly, Rich! It seems to be
>> an actual sound-- something I cannot find the source of, possibly
>> even a transmission. I had everything off, even downstairs, and
>> everything running on DC. Here's a spectrogram of the clock test
>> movie that Gianni sent back in November:
>> http://www.uwm.edu/~type/Mic%20Preamps/MicroTrack_NH900_722Compare2.jpg
>>
>> Gianni recently asked about some High Hz banding he was seeing with
>> his NT1A's, so to get a sense of what's inherent my NT1A's, I made
>> some spectrograms of simultaneous recordings made in a mid-winter
>> very quiet, remote wood at about 2am. (Way up in the hollow Rich).
>> The Sennheiser mkh80 is included for comparison.
>>
>> http://www.uwm.edu/~type/Mic%20Preamps/NT1A_MKH80_Remote2AMPresSpect.jp=
g
>>
>> I could not find any significant banding at any frequency including
>> 13K, so this seems to confirm the 13K sound was recorded, not
>> self-noise. The sample is 3 seconds long and the vertical scale is
>> 0-24KHz. Rob D.
>>
>> =3D =3D =3D
>>
>> At 4:34 AM +0000 1/9/06, Rich Peet wrote:
>> >--- In Rob Danielson <>
>wrote:
>> > In this test,
>> >>
>> > >
>http://www.uwm.edu/~type/Mic%20Preamps/MicroTrack_NH900_722Compare2.mov
>> >>
>> >....
>> >
>> >Did you add a high pitched whistle to go with your clocks in your
>> >recording area or are you now chasing whistles from your nt1-a's like
>> >I have had to do in the past with my old mics?
>> >
> > >Rich
> > >
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