Topic: -12db over explanation sought

[anatta]

This has to be drop dead obvious to others, but on the Sony M10 what does the "-12db over" meter signify?  And more basically, I confess, how is it that there can be any negative db value?  I have been searching online for this answer, but I guess in the wrong places, so far.

Thanks for any guidance.

[aaronji]

I assume you mean the -12 dB and over LEDs?  The first indicates when the signal goes over -12 dB and the second when it goes over 0 dB.  The dB's are negative because the numbers are dBFS (dB full scale), meaning that 0 db is the maximum and all other values are in reference to that... 

[acidjack]

Yup.

And the point being:

1. You want the green lights on more or less consistently (i.e., you want the music at or higher than -12dB when you're recording)
2. You want the red lights on never (because that means the deck is clipping).

[Gutbucket]

You want the green lights on more or less consistently (i.e., you want the music at or higher than -12dB when you're recording)

This really depends strongly on the material.  For loud PA music without much variation in loudness level it might work have that -12dB green light iluminated pretty regularly. But with more dynamic matierial if you were to try and set gain to have that -12dB indicator lit more or less constantly, you'll be using too much gain and will overload and the clip input on the peaks (indicated by the red 0dB light flashing).  The danger of running a recording by clipping is far greater than recording at too low a level.

I'd modify the simple aproach to say: Use the -10dB green light as your target 'good' level peak-indicator by setting your gain so that the the green light blinks only during the loudest portions of the recording.  If the red one blinks at all, turn down the gain by another -6dB (or more).

[rhinowing]

it's probably worth noting that the snare is almost always the loudest instrument in the PA at most rock shows....so make sure that isn't clipping and you should be fine

[aaronji]

I assume you mean the -12 dB and over LEDs?  The first indicates when the signal goes over -12 dB and the second when it goes over 0 dB.  The dB's are negative because the numbers are dBFS (dB full scale), meaning that 0 db is the maximum and all other values are in reference to that... 

To elaborate a little, the red (over) LED goes on when the signal goes above -1 dBFS (from the manual)...

As far as the negative dB thing goes, decibels are logarithms of the ratio of two values.  In audio, these values are usually voltages and dB = 20*log(V1/V0).  V0 is some sort of reference value, such as 0.775 Vrms (dBu) or 1 Vrms (dBV).  If V1 is smaller than V0, you get a negative number...With dBFS, the reference is the maximum input level before clipping so any smaller input (non-clipping signal) will result in a negative.

EDIT: Incidentally, I have not been able to find out what the reference value is for dBFS on the M10.  I read 1 Vrms somewhere, but I haven't been able to find that again...The manual says "Rated input level: 2V" but it is unclear to me if that is a max or more of a nominal level.  Anyone have any idea?

The danger of running a recording by clipping is far greater than recording at too low a level.

It is possible though!  I have managed...Sigh...

[Gutbucket]

it's probably worth noting that the snare is almost always the loudest instrument in the PA at most rock shows....so make sure that isn't clipping and you should be fine

..or the kick drum if they have the subwoofers cranked for that annoying over-emphasized, one-note chest thumping boom effect.

As a general rule of thumb, audience applause is usually the loudest sounds at quieter or acoutstic music events.

[Shadow_7]

I'm not sure what they mean either.  But generally you want your average signal strength to hover between -18dB and -12dB.  That way your peaks, i.e. drums, applause, door slams, mics falling over, drunk guy at the bar belching, and stuff doesn't clip.  Since it's all pretty much a guessing game until AFTER the event.  Distance makes a huge difference in levels.  And some venues are bit more live than others.  Drums tend to double a groups dB output so even conservative guessing can nip you when the whole group starts playing full bore. 

If you know what's going to happen, i.e. scripted, no source louder than known level, you can ride levels pretty close to 0dB.  But you never really know and you can't always be lucky.  Just one helicopter or 1st responder away from clipping if you don't keep a safety margin of sorts.  But I'm sure that there's more accurate info out there beyond just guessing on my part.  All I really know is that if I'm doing more than 20dB gain in post, I screwed up.  Around 10dB of digital gain and I did alright.  Less than 5dB and there wasn't something unexpected there, I got lucky at best.  At worst, no do overs.