OK i wired up the CMRs today
test rig: MK4V>CMR on stand about 1m from a pair of 8" KRK Rokit powered monitors.
channel 1: CMR#1 wired directly to line in with no resistance
channel 2: CMR#2 wired to mic in, with 1.5Kohm resistor inline with signal lead
both mics powered by the "5V" power. it tests at 5.0V (+/- 0.05) without a load, but as soon as i plug the mics in it drops to 4V (which is right at the lower limit of spec for CMR)
had rolloff set to 50KHz just for the heck of it. not really useful in this test but prob how i would use it in the field
line in was surprisingly sensitive. input level goes from -7 to 44 (strange scale but whatever...), and when line in is set to max of 44, similar level was achieved on mic in at a setting of 29. this 15 unit bias seems to be consistent at various levels.
I recorded a bunch of content at different levels, both soft and loud (as loud as this setup would go, i was limited as monitors were clipping, see below for test with better sound source at higher SPL).
the background noise with the db app on my phone was measured at 37 dB. app is somewhat useful but i dont think it reads accurately above 90 dB
heres some samples:
Mark Knopfler "wag the dog" played softly, db meter said 65-70. I cant imagine recording any material quieter than this
audio recorded(raw,low level, some talking by me before it gets going):
https://drive.google.com/open?id=1WpVuOZtGt9F5HQhibXhgy3h8YVIGsCupshort vid of test method (audio from phone):
https://photos.app.goo.gl/QBjaUWu1N8Adv3NfAyou can see the 20 dB level indicators blinking on occasion in the vid, also see how the menu and controls work a bit
for most of it:
left channel, line in, level set to 44, peak dB was 19, RMS was -38
right channel, mic in, level set to 29, peak dB was 19.7, RMS was -38.7
(pretty good level matching for eyeballing! the meters on this are tiny but obviously good enough for our purposes)
near the end of "wag the dog" and for the portion of "working on it", i cranked the level on the right channel (mic in) up to its max of 44. the wag the dog portion had a peak around -6db and an rms around -24. Keep in mind this is very quiet source material, and if additional gain was needed you could swap that resistor out for a 500 ohm.
"working on it" is a quiet acoustic number, and with both channels cranked to the max of 44, left channel line in was -28db peak and -43db rms. right channel mic in was -13dB peak, -28 dB rms
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ok now for some loud material. Here is Eyes of the World from the RFK 89 boxset. my dB meter said ~90 but i think thats where the mic on my phone tops out so lets just say its 90+ dB...
audio recorded:
https://drive.google.com/open?id=1GPFzutHve8NKEUBJfmEhlgbdDusx3uKTshort vid of test method (audio from phone):
https://photos.app.goo.gl/eW5quXemhgd4yG447here we see level indicators constantly lit, occasionally blinking off as it dips below -20dB. if you were peaking at 0 dB they flash red. i have yet to test how the limiter works
here we have something approaching the volume of tapers section at a rock-concert. so we can turn it down and have some headroom
left channel, line in, level set to 32, peak dB was -8dB, RMS was -23dB
right channel, mic in, level set to 18, peak dB was ~ -8dB, RMS was ~ -23dB (this time i matched within a 1/2 dB, again, impressive level indicators)
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ok last test. this is the mics wrapped up in wool socks, and a tshirt, under a parka, inside my car, in a snowstorm. i wanted to test the self-noise of the mics and see if line in and mic in were any different. both were set to the same 32&18 as in the last two tests to simulate normal recording levels of loud material. results were impressive! again this isnt strictly input noise of the recorder, this is with mics attached so that seems reasonable to me, what do you think? note that the mic in actually *looks* a little quieter graphically, but not by much. the stats window i used was goofy. when i highlighted either channel and scanned like i was gonna normalize, it said
left channel (line in): peak:-65.6 dB, RMS -77.8 dB
right channel (mic in) peak:-63.6 dB, RMS -78dB (peak is due to weird tick at 49 seconds)
that should be well below room noise in any case.
Overall i am very impressed with the unit. its my dream gear. great sound, low noise. simple, elegant, bombproof. almost impossible to mess your recording up