Clipping vs buzzing: newbie question

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Grotius

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I'm just getting started miking my grand piano for classical music. I'm using two Oktava MC012s, dbx386 2-channel preamp with digital out, into SPDIF port on my computer. I'm recording in 24-bit/88.1, using Cool Edit. I'm experimenting with all sorts of configurations -- XY, AB, distance miking, close miking, etc. In all those configurations, my noise level is very low, which is terrific (though close miking brings damper and pedal noises); I get a nice clear sound even if my levels never get much higher than halfway on the meter.

My problem is that if my levels get into the 'yellow' or even just below it, I get 'buzzing' sounds on the recording. It's not quite as nasty as the digital distortion one gets with clipping at 0 dbFS. I'm wondering, though -- is my buzzing just another version of clipping and digital distortion? Should I content myself with levels that max out at maybe 2/3 of the meter on my preamp (and waveforms that only make it halfway up to the dreaded 0 db ceiling)? It would be nice if my listeners didn't have to crank their CD players high to hear my (admittedly quiet) Chopin. But that's better than buzzing.

So: is buzzing just another form of clipping? Can I do anything about it, other than adjusting levels downward?

Thanks,

Grotius.
 
I believe the 386 has a special feature built in to it's a/d conversion (Type IV conversion) that acts as a limiter that supposedly can't digitally clip. But if you're going analog out . . .

It might be Toob noise - maybe you're driving the toobs a bit, and need to dial them down a bit in the equation.

I suppose Tom Cram should answer this one, though.
 
Which meters are you talking about? The Pre or CEP?

You could be maxing out the pre before clipping the sound card.
 
Thanks for your replies. TexRoadkill, I meant the levels and meters on the preamp; if they reach the upper third of the meter, I get buzzing. (I watch the preamp's meters as I play; I usually play from memory.) The resulting waveforms in Cool Edit look fine, with the highest peaks still well below the 0 decibels ceiling.

Chessrock, I'm using the digital out on the preamp, and the 386 does have the nifty clip-preventing conversion you mentioned. I have indeed been operating the preamp with the tube knob set in the middle -- midway between +30 and +60. When I dial it all the way down, I have to crank the levels to maximum to get a moderate amount of sound of the thing. I have not tried recording much that way, so I will give it a try.

Could the buzzing be the microphones? Do mics make buzzing noises when they exceed their maximum sound pressure level? Or if they are (shudder) defective?

Thanks! -- Grotius.
 
Grotius said:
Do mics make buzzing noises when they exceed their maximum sound pressure level? Or if they are (shudder) defective?
Click to expand...

I doubt it, but if you're talking about Oktavas bought from Guitar Center, it is always possible you got a defective one. But the chances of getting two defective ones? Not very likely. I'm assuming they came with the -10 db pad capsules, right? You might also want to try screwing those on and see what happens . . . although you probably won't be getting enough signal if you already have to crank the gain up all the way. :)
 
You need to start the tried and true process of elimination to locate the source of the buzz:

Do you get the buzzing from both mics?
Have you tried a dynamic mic in the chain to see if you get the same buzz?
Does swapping mic cables help?
Can you borrow a different preamp to try?
How about the cables from the preamp to the recording device?

You could also try taking the mics and preamp to the store where you bought them and see if you can reproduce the problem there. Then try swapping with another preamp at the store. Could very well be a faulty preamp. Perhaps even a phantom power issue. (That's why I suggested trying a dynamic).
 
Thanks for the suggestions. Wonder of wonders, today I listened to the exact same recordings, through the exact same set of headphones and, later, through some speakers. Presto, no buzzing. Maybe I just didn't have the headphones plugged in all the way last night.

I do have a general question about recording levels. The optimal peak for digital recording is just below the 0dB level, right? (I noticed Harvey suggested keeping the levels of a live classical duo between -6 and -12 dB.) Is that how the optimal waveform should look in Cool Edit? I get confused because sometimes it seems that my loudest recordings (usually voice) have the waveforms with the smallest amplitude. Conversely, a quiet Chopin Prelude may reach -3 dB on the preamp and in Cool Edit, and its waveforms may look like the Alps. So... <...reaching for my copy of "Home Recording for Musicians"...> ... is volume is a function of frequency as well as amplitude?

Confused but learning,

Grotius.
 
With good 24 bit converters, its not really necessary to try and get 'as hot as possible.' The hotter you record though, the more bits you are using, so you have greater dynamic range. So, record hot, but never so hot that you run the risk of clipping.

You bring up a good point with your comparison between your voice recordings and a chopin recording. There are really two factors to consider with your example. First, theres this thing called the fletcher-munson equal loudness curves that show that the perceived loudness of a sound does depend on frequency. Heres a link: fletcher-munson The other point you bring up about the 'alps' touches on a different, but related topic. The loudness you perceive is not related to the peak level of a signal but more closely to the average or RMS level of the signal. So, a chopin piece that has lots of transients (hence a high peak level) may be perceived as quieter than your voice recording that is smoother and doesn't have the same peak level, but has a higher average level.

Hope this clears things up for you.
 
<< So, record hot, but never so hot that you run the risk of clipping. >>

Thanks for this advice. I'm getting good results following this approach. My basic noise level is around -60dB, which is almost inaudible to me, so even when I play pianissimo, I hear Chopin and no noise. (I suppose my ears will get more sensitive as I record more, but for now I'm still shaking my head of magnitude of the improvement over my old setup -- minidisc to analog line in on soundcard.)

<< the perceived loudness of a sound does depend on frequency.>>

Ah, I thought so. Thanks for the link; it was very helpful. It may help explain why I hear too much treble and not enough bass in my piano recordings. Then again, my inexpert experiments with miking may have something to do with that. As might the voicing of my piano. As might my left-hand playing technique...

<< So, a chopin piece that has lots of transients (hence a high peak level) may be perceived as quieter than your voice recording that is smoother and doesn't have the same peak level, but has a higher average level. >>

Got it. This makes sense to me.

<< Hope this clears things up for you. >>

Yep! Thanks again.
 
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