At 11:25 PM +0000 1/3/07, jpbeale wrote:
<snip>
>
>
>My reported noise level is for the ~80% of the time that the MD motor
>is not spinning. It gets about 2 dB worse when it spins up; see also
>http://beale.best.vwh.net/measure/audio/RH1-noise/index.html
I try to avoid using portions of the recordings when the disc is
writing in my A/B tests so I don't have a sense of the audible
impact. I've not detected a change in the s-n when recording in very
quiet places with Rode NT1-A's with the Hi-MD pre at max gain as the
writing operation comes and goes. I'll listen for this more carefully.
.
>
>I had the in-unit display ON during recording. I suspect some
>high-frequency noise spikes might be reduced had I turned it off.
Makes sense.
>
>(measurement notes:)
>------------------------------------------------
>1 kHz sine from Protek B-801 sig gen:
>
>Tek TDS210 scope: 4.00 Vac RMS (+12.04 dBV)
>Fluke 77: 3.93 Vac (+11.89 dBV)
>RS 22-168a meter: 4.02 Vac (+12.08 dBV)
>Tek DMM916: 3.96 Vac (+11.94 dBV)
>
>------------------------------------------------
>Echo MIA control panel sets output level (+4 dBu or -10 dBV)
>plus master fader from +0 dB to -40 dB.
>
>Echo Audio MIA line out 1 kHz sine @ +4 dBu setting
>measured by Tektronix TDS210 scope
>
>-40 dB: 60.6 mVac
>-20 dB: 0.625 Vac
>-10 dB: 1.98 Vac (+5.93 dBV)
>-5 dB: 3.54 Vac
>-3 dB: 4.44 Vac
>-1 dB: 5.61 Vac
>+0 dB: 6.29 Vac (+15.97 dBV)
>
>Echo Audio MIA line out @ -10 dBV setting
>
>-20 dB: 0.153 mVac
>-10 dB: 0.485 Vac
>-6 dB: 0.787 Vac
>-5 dB: 0.883 Vac (-1.08 dBV) <=3D=3D TEST LEVEL
>+0 dB: 1.57 Vac (+3.92 dBV)
>------------------------------------------------
>L: HOSA XLR att #1: -25.13 dB + JPB cable -40.07 dB =3D -65.2 dB
>R: HOSA XLR att #2: -25.10 dB + JPB cable -40.10 dB =3D -65.2 dB
>
>-1.08 dBV + -65.2 dB =3D -66.28 dBV
>
>however the gain of the RH1 did not precisely match the signal at
>0 dBFS. By comparing output and input files, I determined that the RH1
>file 0 dBFS was actually -65.78 dBV or -63.58 dBu at the input for the
>test data reported here:
>http://beale.best.vwh.net/measure/audio/MZ-RH1_Mic_30_150Z.htm
I _was_ headed towards majoring in engineering at one time,..wish I
could follow along. Coincidentally, I came-up with an estimate of
-122 to -126 dbu (A weighted) for the Hi-MD mic pre based on
dividing the difference in noise between that of the Sound Devices
722 and that of the Hi-MD into audible steps. Thanks for making the
report available. Rob D.
>
>regards,
>John
>
--
Rob Danielson
Peck School of the Arts
University of Wisconsin-Milwaukee
http://www.uwm.edu/~type/audio-art-tech-gallery/
|