Let me be very blunt: Both of you guys' descriptions of what equipment you're using and how it is connected are not the clearest. When you're trying to troubleshoot a setup, you need to be very conscious of every stage that the sound, the resulting analog signals and the eventual digital data are passing through. Any one (or more) of those stages may be causing the problem.
Your first approach should be to try to find ways to "tap into" the recording chain at various points along the way to see whether the signal is good or no good at that point. You want to find the first point (in the forward sequence of signal flow) where things are bad, then work backward toward the source until you find that they are not bad. Whatever's in between is causing the problem.
Just from general experience I find two problem areas to be the most prevalent. One is that a microphone which ordinarily could handle high sound pressure levels will be unable to do so, because the powering provided by the preamp or recording interface is inadequate. Sorry to say, especially with lightweight portable equipment, the words "phantom powering" are often taken to mean whatever their manufacturer wants them to mean, instead of "This circuit complies with the recommendations of the DIN EN 61938 standard for phantom powering." Thus a quick and useful test may be to shut off the microphone powering in the preamp or interface, and substitute a known good phantom power supply (assuming that your microphones are designed for standard phantom powering). If in doubt, measure--we can talk about how to do that.
The other big problem area for live, high-SPL recording is that the analog input circuitry of the preamp/recorder/interface (whatever the microphones are directly connected to) is overloaded by the voltages coming out of the microphones at high sound pressure levels. Many preamps have "overload" LEDs or level indicators of some sort--but in nearly all cases those indicators are tied to the output stage of the preamp or interface. If the voltage at the preamp input is overloading the first stage of the circuit, those indicators won't know about it, and from then on you'll have a permanently distorted (clipped) signal. I have one very popular little preamp here which I keep because it's such an extreme example: depending on how you set its gain knobs and switches, it can merrily pump out 25% THD before its "overload" light comes on, while with different settings, the "overload" light actually serves as a useful warning.
A quick test for this type of overload is to use resistive pads at the inputs of the preamp or recorder or recording recording interface. If you're plugging your mike cables into XLR sockets, place 15 or 20 dB in-line pads (Shure makes good ones, so does Audio-Technica, so do a lot of people; they're cheap and foolproof and belong in every gig bag) at those inputs. If you do that and the problem goes away, you've got the diagnosis and the cure all in one. I can't recommend this highly enough.
It is also far better sonically than using the pad switch on the microphones; the pad switch on a microphone should NEVER be used to solve preamp overload except in a dire emergency. Of course if the microphones themselves are being overloaded by high sound pressure levels, then you have no choice, although even then I would double-check the microphone powering since the #1 symptom of inadequate powering is that the microphone can't handle high sound pressure levels. As a plan "B" I would also suggest trying a basic foam windscreen just in case, since air currents can cause pressure-gradient microphones to put out enormous infrasonic energy which may cause overload even if you aren't hearing any wind noise in the main audio range; occasionally that is the problem.
In other words, when problems arise, you can't just continue to look at a typical recording interface or preamp as a single unit, even though it's contained in a single, small housing. You have to break down its functions in terms of microphone powering, preamp input, preamp output, a/d converter input, etc., because (possibly depending on user settings) any given stage of the unit may be where the problem is occurring.
I can't guarantee that the problem is in either of these two areas, but they are certainly the two areas where I see the most problems in the portable equipment I've tested. In both cases a minimum of test equipment would save a lot of time and trouble--I'm very fond of my NTI "Minirator" and "Minilyser" (signal generator and level/THD meter respectively) but there certainly are cheaper alternatives.
Also, if you have (or can borrow) any reliable substitutes for any part of the setup, you can try swapping parts around until some combination that should work doesn't work, or until something that wasn't working with one set of components does work if you just change one part of it.
--best regards
Topic: WAV - squared off - what happened here? (Read 6629 times)