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Gear / Technical Help => Ask The Tapers => Topic started by: KLowe on October 20, 2007, 12:06:09 PM
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Hello people with all the knowledge.
I'm pretty sure I brickwalled some shows from the Echo Project. I ran a 143's > mini-mp > R-4 (line in).
I set the levels pretty agressively on the mini-mp but no clipping indicated on the meters. Gain was set at zero on the R-4 and no clipping was noted on the R-4 levels. So...I thinks everything is going along fine.
Get home and load up the wave for and sure enough...that mofo "appears" to be brickwalled.
I'll post a pic of the waveform as soon as I figure out how to capture a screen image. The waveform looks "boxy" and does not go to 0 db like clipping.
Question. What exacly is "brickwalling". Is it that the outboard pre just sent to much signal for the R-4's A/D to digest? If so... then howcome no "clipping" was noticed on the R-4's meters?
Thanks in advance.
KLowe (Newbe)
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does your waveform look like sticks of butter? :P
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does your waveform look like sticks of butter? :P
que?
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does your waveform look like sticks of butter? :P
que?
you said your waveform looks "boxy"...those are the dreaded sticks of buttah ;)
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does your waveform look like sticks of butter? :P
que?
you said your waveform looks "boxy"...those are the dreaded sticks of buttah ;)
yes. Then. They doo look awefully alot like butter sticks.
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Hey Moke,
it was line in. from the apogee to the R-4
anyone have a free program that takes screen shots? I want to post a pic of the wave form.
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anyone have a free program that takes screen shots? I want to post a pic of the wave form.
windows does ;) hit printscreen then open paint, photoshop etc and open a blank project, hit paste and there you go.
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By setting the R-04 level at zero you were actually crushing the signal that the Apogee was sending. The Apogee was not overloading but by going line in to the R-04 you will need to add a little gain on the R-04 to make sure you are setting proper gain structure.
Run the Apogee a little lighter next time and set the R-04 to about 3. This should solve your issue.
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cool. Thanks. I'll definately have to try that out.
Thanks all yall for the advice.
Kevin
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Look at the SPCIFICATIONS FOR THE R-4 LINE INPUT. If I remember correctly, it is ~+4 dB unbalanced, and ~+9 dB maximum running balanced LINE input.
Now look at the maximum output (before clipping) of the preamplifier you're using. If the full output of the preamplifier is GREATER THAN THE INPUT ABILITY OF THE DECK'S INPUT, THEN DO NOT RUN THE PREAMP AT MAXIMUM OUTPUT into the deck, or at least without using a suitable attenuation network to keep the deck from being overloaded.
Most decks these days do NOT have full signal input reduction level setting ability. And YES, your VUs might look OK, but an input stage on the deck that's BEFORE the level setting on the deck can get slammed to clip anyway if input level exceeds deck's maximum signal input specification.
My tips page has some notes on avoiding MIC input overloads on portable decks, but sometimes same suggestions on noting level adjustment settings may also help keep LINE inputs from being clipped even if not knowing maximum dB output/input specs.
www.sonicstudios.com/tips.htm (http://www.sonicstudios.com/tips.htm)
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Posting for reference...
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KLowe, you used a preamp to raise microphone signals to line level, then you fed those line level signals to the line inputs of a recorder. It helps to think of your setup as a series of consecutive "stages" that the signals go through. You apparently set the recorder's level controls properly so that its meters never reached 0 dB (full scale). That rules out one possible way of causing an overload, which is good, but there were still at least four other possible stages at which it could have occurred:
[1] The sound levels at your microphones could have been greater than the microphones were capable of handling.
[2] The voltage put out by your microphones could have been greater than the inputs to your preamp were capable of handling.
[3] Preamps are basically "voltage multipliers." If you send 0.01 Volt into a preamp that you've set for 40 dB gain (which is a factor of 100 in voltage, assuming a high-impedance load), you're asking the preamp to put out 1 Volt at its outputs. That's usually fine, but then if you send in 0.2 Volts instead, suddenly you're asking the preamp to put out 20 Volts, which may well be more than it can put out. In effect you're overdriving the output stage of the preamp if you do this.
[4] The voltage put out by your preamp could have been greater than the inputs to your recorder were capable of handling.
Not knowing the characteristics of your particular equipment, I can't say which of these is most likely. But the general concept is to locate the problem by considering each successive stage in the setup.
Keep in mind that many preamps don't indicate input-stage overload (item [2] on my little list); if they have "clip" indicators, they generally are attached only to the output stage (item [3] on the list). So item [2] can be a real problem in live recording because you can't see it happen while it's happening--it just happens.
I only use preamps whose inputs I know can handle the full output voltage that my microphones are capable of putting out; then I never have to worry about it. But if I did have this problem, then resistive attenuators ("pads") at the preamp inputs would be the first thing I'd want to try. They're cheap, they're easy to use, they're reliable, and if you use pads that have just enough attenuation to avoid overload, they don't make the recording any noisier than it has to be.
--best regards