Multitrack Reality - A question and a report back

ullanta said:
Umm... dude... not at all. Seriously, an SM57? Try the same with a C414... An SM57 has a sensitivity of about 1.6mV/Pa; my KR-1Fs are about 12 mV/Pa; a large diaphragm mic like a C414 puts out around 23 mV/Pa. A low-output dynamic is NOT a useful tidbit of information here!
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Sorry dude, I won't be shouting from 1" away at the top of my voice into either of my AKG 414s, nor will I do so into either of my U87s, my Sanken CU41, Lawson LMP47 or my U47. I like them too much.

Sorry again, but this is not useful. Can you play some Schumann at concert level? Especially if you're holding a meter with one hand, you can be sure you're not generating anywhere near the max level of the instrument. Distance matters... a lot. The DPA 130 dB measurement should be pretty reliable, they're not idiots.
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Evidently, yes, they are.

You've spent too much time reading articles.

Game over

Best of luck
 
Look this is getting ridiculous. Peizo's are used in some contact mics and if you hit that hard enough you can get some very serious voltage. This is however a list for sound in filmmaking not Recording for the battle of high dB's. Ullanta is right that your tests while interesting don't really lead to the conclusions you have drawn. The music I've recorded a lot is "New Music" (I hate the term but ... that's what it's called) and it at times has over the top piano and percussion. I would not be surprised that levels inside a piano going full out could be over 130dBu, percussion can certainly be in that range.

Arguments about preamp design aside his basic point was that with close micing very loud sources he has gotten the MixPre to overload. That's not my experience but I'm not doing exactly what he is doing and I have no doubt that he is reporting accurately. You can't go and say "you didn't clip" based on specs, especially ones that seem to be somewhat open to interpretation.

So how does this relate to the topic? Well if your doing normal filmmaking probably not much. Your never going to see levels like that except when you bump the mic. If your doing a concert film it still probably doesn't come into play (unless you are the concert sound guy - but then why would you be using the MixPre?). If your recording scoring for a film this could be an important bit of info, or poss a film with a close shot piano that you want to get a great recording of. In other words keep it in the back of you mind and if a situation comes up like this think about options, in stead of getting surprised.
As I said I have not had any problems. But I will keep this in mind until/unless I do my own tests and decide I have better info. for me.

And I have to admit that he is also right about the pads on mics. They only lower the signal down the line and the only real reason for them is to keep from clipping the input stages of mic pre's. That sort of points to the idea that they wouldn't be there if this wasn't a problem at least historically.

And finally Ullanta,
it sounded like you had the limiters set "close to 0". Maybe I'm miss reading that but that would be way low for a device that can out put over +20. I operate with the limiters at there highest setting. This wouldn't make any difference on the non limited clipping but would certainly eliminate that heavy compression your getting. Though of course if your constantly clipping with out the limiters you will be compressing with them.
 
Hi Noiz!

I don't think I meant to say the limiters were set for 0 - frankly, I haven't yet played with the limiter setting since I got the MixPre a fortnight or so ago, but it seems to be coming into play at a reasonable level in general (around the last 2 red lights on the meters in situations where the inpute level doesn't seem to be the issue).

However, I'm not sure what the limiter threshold setting affects - I suspect it deals only with the output limiter. If you have any more detail or experience with this, please let me know - I'm not sure how soon I'll have a chance to play with it again. In the meantime I'll see if SD says anything about this... The limiter is one of the main reasons I'm even playing with the MixPre for these quick'n'dirty recording applications, and I'm very happy with the way it's working for output level limiting (that is, pretty much never unless something really unanticipated happens).

Small Update - yeah, the MixPre user manual (p. 7) says of the 2-stage limiter "the first stage keeps the input gain stage from clipping; the second stage limits the variable gain stage to the level set by the Limiter Threshold control". This seems to indicate that the first stage is fixed (tailored to the input clip level)...

For a real further aside, it's interesting to me that there's so little easily available information on the web about SPL levels for various things, and especially about the same things at varying distances. Maybe we should start putting together a database of sorts that has more useful info than shrimp chewing plankton and jet planes at 100 feet...
 
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I believe the drop is square of the distance (Logarithmic? too long since I had a math class). So distance makes a very big difference. My problems with the jets wasn't so much distance as that they were supersonic , or close, and the sound hit you like a punch, but after they had passed. So you had to keep lowering the level and hope the next pass worked because it was just WHAM and gone.
 
Yes, sorta "logarithmic from a point source in an open space"... but instruments, of course, are designed to shape and direct the sound... and a grand piano, especially... I don't think a straighforward calculation would work in the range of roughly the size of the piano. As I'm sure you know, the "sound" of a grand piano doesn't exist near the piano; it only all begins to blend together properly a few feet away... I suspect sound gdropoff would be a lot less than logarithmic anyplace in the lid/soundboard triangle, or right outside.

The same goes for most sources, I'd imagine... the human voice, a car, an airplane... there's some range (which I intuit as similar to the size of the source) in which things are... well, unruly.

As you say, Noiz, this is all far aside from common filmmaking concerns! Maybe we should take the whiole discussion somewhere else.
 
Actually the fall off is of importance to filmmaking. It's one of the reasons camera mic's are almost never a good choice. The fall off is fixed for a given situation (humidity, wind direction etc). Your talking more about sweetspot, and that is very dependent on source. Also with something as large as a piano you could/would have reenforcing reflection patterns so the drop would not be as linear for all frequencies. With very few exceptions (involving some sort of physical amplifier or collector) sound always drops away with distance. A fun exception is a pair of really large parabolic reflectors aimed at each other. a sound source at the focus of one will gather at the focus of the other. So you can whisper across great distances. But that kind of thing is very unusual in nature.

What was this thread about??? ;~)
 
ha ha, i was reading it thinking the exact same thing! no big deal... im in zambia at the moment, spent the day rigging today. and will commence shooting tomorrow.

sound check sounded great, so here goes!
 
Noiz2 said:
Also with something as large as a piano you could/would have reenforcing reflection patterns so the drop would not be as linear for all frequencies. With very few exceptions (involving some sort of physical amplifier or collector) sound always drops away with distance.
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'zactly what I'm sayin'! That is, there's a distance (and likely direction) at which you can start thinking of any source as a point source and calculate dropoff, etc... but when very close (or inside) things are different.
 
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