Topic: WTF? Strange waveform

[itook2much]

Taped Roy Clark Monday night, with a screaming hillbilly beside me who thought she was gonna win the ThunderClap award or something.

When processing, found this odd bit several times, always right at a point when she was clapping right by my head.  Is this what a harsh clip looks like, or something else?  Never seen anything like it before when editing.

[SmokinJoe]

Possibly the air pressure from the woosh of her clapping, as much as the sound itself.  Much more so on one side, which would make sense obviously.

[itook2much]

Thanks to both of you. +t

Unlike her, the drums & cymbals aren't right by my head luckily

[Petrus]

I got these when recording shotgun blasts with DPA 4060:s... (about 6 m away from the muzzle, thank god). The rising part is smooth, then regains normal jiggynes, yes?

I think what we see here is physical clipping of the mic capsule. It goes deaf for a few milliseconds. Surprisingly it does not sound all that bad.

[DSatz]

Petrus, I'd like to see a more detailed screen shot, but I basically had the same reaction as you--I thought "overload." I've seen a similar pattern when I deliberately provoked overload in a Schoeps mike by screaming/growling right into it with no windscreen. I think my upstairs neighbors suspected that something violent was occurring down here, and I got a sore throat within less than a minute.

The thing is, we're seeing the result at the far end of the "recording chain." Anything along that route could have been the "overloadee"--the microphone, the preamp (and even there it could be input overload or overload in an output stage), or the input stage of the A/D converter. The one thing we can pretty much infer from the shape of that waveform is that it was very likely electronic overload, because there's a very characteristic DC restoration curve with a time constant after the peak excursion.

But actually, in a condenser microphone, the circuitry typically reaches its overload point long before the capsule ever will. A microphone capsule tends to have only gradually increasing distortion at higher SPLs, while the circuitry normally has a sharper increase in distortion at some fixed output voltage (though if it's driving too low a load impedance, that limit will come distinctly sooner, and if the powering is inadequate, it can be a lot sooner--all out of proportion to how "almost right" the powering is in some cases).

Anyway, if the loading and powering of the microphone are up to standard, typically (he says, attempting to summarize the general behavior of thousands of different microphones) the capsule can handle from 20 - 50 dB higher sound pressure levels than the circuitry can. This is why some microphones have pad switches, or for some modular systems, capacitive pads that go between the capsule and amplifier. Those things lower the input sensitivity of the circuitry, on the assumption that the capsule is having little or no problem but that the amplifier's input is being pushed too hard.

--best regards