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Gear / Technical Help => Ask The Tapers => Topic started by: jmz93 on December 03, 2007, 12:28:22 AM
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I hope this is the best place to post this. I have no idea what part of my rig is causing this
aweful result. First, some samples of what I am going to describe are at:
http://www.sendspace.com/pro/dl/1ozdj2
I've never heard distortion like that in many years of recording! WTF???
The one music sample goes clean for a brief instant, providing a glimpse of what the recording could have been
like - i.e. spectacular! In an audio editor, nothing
shows as hitting 0DB. So what gives? Where s that aweful clipping coming from then?
There's nothing wrong with the wave files, according to the free fixwav.exe utility,
i.e. the file headers are fine.
Rig: SP-CMC-4's > Church Audio ST9100 preamp (on full) > Nickspicks silver cable >
R-09 line in, gain at 13/30(unity?), 24-bit/44.1KHZ wave.
Fresh batteries in everything, clear SD card, all gear in pockets except for mics which were attached to
the shoulders of my sweater.
and yes, I was definitely plugged into line in, not mic in.
The show was loud but loud on jazz terms, nothing like rock levels.
All through the show I kept thinking "Oh man, this is going to be the best tape I've pulled in years ..." only
to discover 3GB of *THAT!
Any ideas folks? Believe me, once I find the ulprit piece of gear,
it's being replaced ASAP. I can't have things this unreliable for stealth...
(sick, frustrated, mad, time for a beer...)
Chris
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nevermind
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Damn double post.
Sounds more like a bad cable than anything. Particularly because it goes in and out. My guess is that when you move then the cable is shorting.
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Either that (bad cable) or a minplug being jostled/pulled part way out of its jack. Have you tested all the parts of your recording chain at home in an attempt to reproduce and isolate the problem?
Might also be an issue with the connection of the minijack to the R09's circuit board, several folks have had problems with that.
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NEWBIE QUESTION-
How do you play those files?
I clicked on the link and downloaded the files...I see them there "dirt clean dirt" or whatever... .flac
I opened them in winamp and they look to be playing....but no sound...and the sound is on/I can play other stuff???
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He notes above that they are 24 bit and Winamp sometimes pukes on playing that bit depth. Try Foobar.
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With +20 of gain on the 9100, are you certain you didn't overload the pre? I have done that before, but only at a loud rock concert. My 9100 has a red LED that indicates if the levels are too hot.
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i'd bet money it's the jack on the r-09. i had the same thing happen to me last year. there have been many issues w/ the r-09 input jack. do a forum search and you'll see many folks here have had problems.
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I don't think that it is gain related as you can here it come in and out during the quiet passages too. I am going with the input jack as well. I seem to recall there being a persistent problem with those.
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This is flat out digi-noise, not the random sounds of loose connection although I suppose a loose board connection could cause more than just a sort of random static type of sound. This is definitely not the sound of mic clipping either.
I'm laying odds that you have a slow SD card...such as one of the cheap Transcends.
What happens is that the SD card can't keep up with the needed write speed for 24 bit, since so much data needs to be written to the card in such a short time.
You might try to record at 16 bit and 44.1 and see if the problem goes away. If so, then it's the speed of your card. For the R-09 running at 24 bit, you need the faster speed SD cards.
I had this problem with a lower speed 4 GB Transcend in an R-09 that I ran for a couple of shows, although the digi-noise was more pronounced and caused more distinct drop-outs than I'm hearing here.
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What version of firmware do you have installed in the R-09?
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thats a really good point about cheap sd cards, i never knew that. try to make a recording at 44.1 see if problem goes away. if not, open it up and check that jack. what you're saying sounds exactly like what happened to me. especially since the gear was in your pocket that when a jack could get broken. cable plugged into jack and stuffed into pocket move the wrong way and the thing breaks. was it a sraight or right angle connector? we found that right angle plugs work best for R-09. a straight connector can put alot of strain on jack if its bumping around inside a pocket. good luck
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He notes above that they are 24 bit and Winamp sometimes pukes on playing that bit depth. Try Foobar.
Thanks a bundle!
+T for taking the time to help me!!!
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Thanks for all the replies guys and the ideas. I haven't had time to run tests yet,
but I will. I didn't think of that with the SD card, I'm running firmware 1.30 and as far as I know, the card is an 8gb HC2.
Before firmware 1.30, I was running the same card with no problems, but with a few gigs of stuff pre-loaded,
so that it wouldn't encounter the bug of creating hundreds of tiny files when the autosplit point was reached.
Anyway, I'll run some tests and get back to you.
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If you find it to be the input jack problem as described, I can fix it for you and modify it so it does not break again...I've repaired over a dozen of those bad boys, design flaw IMO. Do let us know what you find.
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I don't know that this is your problem, but I'll throw this out as brainstorming possibilities... :hmmm:
I have an ST-9100 and an R-09. I've noticed that there is an RF type interference when the two items are close together... i.e. I don't put them in the same pocket!
Seriously, plug in them in with a patch cord, no mics, turn them on like you were recording, and put them face to face. Then move them apart a few inches and back together, you can get a little bit of noise when they are together. It's fairly steady, kind of like a 60 cycle hum, but higher pitched than that. You know all those electronic devices which say "complies with FCC part 15 subpart B"? That's what this is all about... some electronics generate noise that bother other electronics.
That said, the noise isn't very loud, in my case, down around -30 or -40 db, but if you superimpose it on your audio signal, it might create this kind of thing. And to rationalize the fact that it comes and goes, I would guess that as you move around in your seat a little, the items move and aren't quite in the same face to face location... they move around a little.
Again... just food for thought...
Seperately, with slow writing to flash cards... won't that show up as skips, rather than noise?
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I don't know that this is your problem, but I'll throw this out as brainstorming possibilities... :hmmm:
I have an ST-9100 and an R-09. I've noticed that there is an RF type interference when the two items are close together... i.e. I don't put them in the same pocket!
I've noticed that too. But, the R9 and preamp were in separate jeans pockets.
But yes, the R9 does pick up RF interfearance fairly easily. Either that, or it's the R9's processor generating noise, that is picked up by the ST9100 and fed back to the R9.
Still messing around with everything - will let you guys know what I discover.
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Still messing around with everything - will let you guys know what I discover.
Update! Problem solved, but the mystery continues.
1. Ran several recording tests with the R9's internal mics, and with a Sony ECM-907 ... no problem, no clipping or wird digital distortion,
including when running at 24/48. So, it's not the recorder, and the line in and mic in jacks are both still solid.
2. Attached AT853's, ST9100 preamp, Nickspicks silver cable with right-angle Neutrik connectors between preamp and R9.
Go into REC/Pause, monitoring through headphones. I hear whisper-quiet ambiant noise from the room,
computer fan noise off to one side, etc. nice stereo spread. I start talking quietly and approaching the mics. Once I get
right on top of them, a louder word from me sends them right into that weird digital distortion. I wait, and oddly, the ambiant room noise is
no longer spread out in stereo, but sounds more mono,and is quietly pulsing/wavering. Oddly, any noise louder than
a whisper is all distorted. Not just loud plausives, but everything.
3. I touch the mics slightly, and once my hand contacts them, bumping them a little, the digi-noise goes away. Nice ambient soundfield again.
4. I turn the preamp down, the R9 down a bit, etc. Still, although the overall level being recorded is down,
once I hit the mics with a loud sound they switch from behaving to crazy distorted. Wait a few seconds, tap the mics with my hand
and noise goes away.. Repeat test over and over again baffled.
5. Fresh battery in preamp, same results as before.
6. Although the cable from Nick looks sound, conducts a stereo signal just fine or appears to anyway ...
I decide to swap it for an old Radioshack 6' 1/8"-1/8" chord. Cheap construction and straight ends.
Repeat test and ... amazingly, I can stick one of the mics right in my mouth
and yell, and nothing happens! Things clip a little, but it's regular-sounding
brickwalling, not the weird digi-noise of before. it's just regular clipping, the result of things being too high for the
hot level being captured by the mics. Whatever I do, turning various things up far too high, jostling the mics around, etc.
i cannot get them to do the odd things they were doing when Nick's silver cable was in line.
so, could this be some sort of grounding issue, introduced by the more expensive cable? Like I said, it
functions, it conducts a signal... but it acts up with loud signals, then behaves once I physically touch the mics.
I'll use the cheap Ratshack cable for now, and things should work fine!
Glad to have narrowed it down to one component, but I'm still at a loss as to
why things go haywire with what appears to b a much better cable, and why a sound source beond a certain threshold sends some part of the chain
into weird digital distortion or ossilation.
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an ounce of prevetion is worth a pound of cure. the input jack is flaky, its a matter of time before it goes. i've seen the mods done by schoepsnbox and they are worth it. you'll never have a problem w/ that jack. also, i'd get a cable with a right angle plug.
-Mike W.
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One possibility not yet mentioned is the external mic preamplifier itself becoming unstable (oscillating at very high frequency) with different output cable capacitance/inductance loading of the pre's output amplifier.
Hitting the preamp with a fast strong signal is usually a good way to make an amplifier circuit show instability modes (ringing/oscillation). This seems what is occurring with mic signals that suddenly get stronger, maybe causing the preamp to go unstable.
This can creat a very large inaudible signal with chance of slamming deck inputs as AC/DC overload.
No easy way to test for this as usually not audible, being at >20,000Hz high frequency, short of attaching an oscilloscope or some other (non-interfering) way to see the pre's output signal while connected to a particularly troublesome interconnection load.
Another quick check is to solder an in-series 50-to-100 ohm resister to each amplifier output that 99% of the time solves an instability problem with little other affect on the preamp's usual performance. If the problem goes away, then amp instability gone with fix already in-place.
Otherwise, if still having a problem, you can leave resisters in place anyway as these are standard on many amps driving cable, and a good design-in for honoring 'Murphy.'
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What Guy says make sense.... here is my take, which may be the same thing, or something different, I'm not sure.
When an electrical signal travels down a length of wire and hits a high impedence endpoint it has a certain amount of reflectance back up the wire... and possibly the signal builds on top of itself in a resonant fashion. On some types of communication cables we put resisters at the end to absorb that energy. As a ham radio operator I vaguely remember that you cut coax to certain lengths, which are typically an even multiple of the appropriate wavelength, not just "this ought to be long enough to reach". Ever hear the the min length of a digital coax patch cable is 1/2 meter? I suspect this is a similar situation.
Basically this is the electrical equivalent of "my car shimmies at about xxx mph... less than that OK, more than that OK". At just the right frequency everything builds. Kind of like that famous bridge (Tacoma Narrows???) which swings and rolls and shook itself apart... a little bit of energy builds in a resonant fashion and gets out of hand.
Like the bridge, it's not an easy thing to predict or calculate. 99% of the time it's not a problem. Maybe the engineers at some of the big cable manufacturers have a simulation which helps them avoid these resonances, but when one of us makes a cable "Oh, I want it just long enough to go from this pocket to that pocket, with RA connectors", etc., there is that 1% chance you will get that situation. It doesn't mean Nick makes crap cables, or that Chris makes bad preamps, it's just that unfortunately once in a while we plug combinations together and get things that no one could predict.
Bottom line: Shit happens. :hmmm: