I wish I could make some useful suggestions! There's bound to be some
hiccups in the establishing any method-- especially one that can
duplicate the manuf numbers consistently ;-) (I'm especially
disadvantaged in that I've not done any such bench work! :-[) Dan
Dugan could have some thoughts about the Audition scale question or
you could pose the method questions to the micbuilder's list. Eric
Benjamin subscribes to this list and might be thoroughly amused by it
all.
I arrived at my "75dB" gain for the NH-900 based on about a half
dozen tests in which the soundfile produced with NT1A's thru
RollsPB224->NH900 was consistently 5 to 7dB more saturated than that
produced by the 722 with the same mics. The 722 was always set to
full, 70dB, gain and the NH900 set at "28" (of 30). I have divided
the noise difference between the 722 and NH900 into 5 and 7 audible
steps the two times I've tried so I've assumed its EIN to be
somewhere close to -125 to -123 dBu (extrapolating from the 722's
figure). Rob D.
At 7:24 PM -0600 4/5/06, Bruce Wilson wrote:
>Well, here are my first measurements. There are some puzzlers here.
>
>All are measured with no mic rolloff, level controls turned up all the way=
,
>with a 150 ohm resistor in the mic input. Resulting recordings were
>FFT-filtered to a flat 20-20k passband, and the noise analyzed to calculat=
e
>the average rms power in dB relative to the full-scale power, using a
>sine-wave standard.
>
>I'll space-format a table of the results. Hopes it comes out okay.
>
>Recorder dB-FS gain A-EIN-FS FS EIN
>Marantz 670 -62 48 -110 -8 -118
>SD722 -78 70 -148
>Sony NHF800 -72 75* -147
>Jukebox 3 -56 48 -104
>
>dB-FS is the 20-20k unweighted noise level in dB relative to full scale.
>gain is the gain of the preamp, if known.
>A-EIN-FS is the Apparent EIN relative to the Full-Scale level.
>FS is the full scale level in dBu (0 dBu=3D0.775v).
>EIN is the measured EIN value in dBu.
>
>*I used the value of 75 dB for a different Sony MD recorder for this figur=
e.
>Sony doesn't say what it really is, so I've used the value Rob mentioned i=
n
>another post (http://groups.yahoo.com/group/naturerecordists/message/21105=
).
>
>So, I hoped you noticed the problem with the SD722 and the MD. Both are we=
ll
>below the theoretical minimum EIN of -136 dBu for a 150 ohm resistor. My
>only conclusion is that either my technique sucks, or both must have a ful=
l
>scale level that is well in the positive dBu range. To make the SD722 matc=
h
>the published specs for this test ("-128 dBu max (-130 dBV), 150 ohm sourc=
e,
>20 Hz-20 kHz BW flat filter, gain fully up") the FS level must be +20 dBu.
>Frankly I doubt this, and am uncomfortable with the results.
>
>Thoughts?
>
>At first I thought it was a problem in the way Audition measured levels.
>There everything is called "power", but upon reflection I think everything
>we call "levels" really are powers because the old reliable dB=3D20log(v1/=
v2)
>is a power form of the dB calculation (based on P=3DV^2/R). The -78 dB for=
the
>722 is much lower than it was before the bandwidth was cropped.
>
>By the way, the Jukebox3 has a very funny noise signal: it's really a 90 H=
z
>sawtooth waveform with some noise on top of it. Got to be the disk drive.
>
>Bruce Wilson KF7K
>http://science.uvsc.edu/wilson
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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