How loud is 85 db(A) comparing to 85 db(C) ?

You need to go search out "loudness curves". When you learn a bit about it you will understand that you are not asking the question in an way that makes it easy to answer.



The curves account for how we perceive the relative loudness of different frequencies when they are at the same energy level... or how we need different energy levels at different frequencies to perceive that they are all the same loudness.

The C curve is fine for your use and the most important thing to do with your SPL meter is to try to use it to achieve consistency rather than to measure, or set to, an absolute SPL.

best regards,
mike

Oh and the B filter is about half way between A and C - in the low frequency roll-off. And don't worry about the D filter, it's just weird (11dB boost at 3.5kHz).

"This means sounds will be louder when measured with a C filter"

with all due respect, this is an illogical statement and I think it reflects the difficulty of answering the question as it has been posed.

I think it's more proper to say...

If, with a C filter the SPL at a measurement position is "X"dBSPL then the energy level for the lower frequencies is much higher than if one used a A filter at the same measurement position and recorded the very same measurement of "X"dBSPL. Obviously the source material being testing would have to be altered between measuring with A and C filters for this to be experienced in real life. 

similarly,

If, with a A filter, one measures "X"dBSPL at a measurement position and then uses the same source material and the same measurement position to take a reading with a C filter the dBSPL will appear to be much lower.

Confused yet? :-)

very best,
mike


edit to add: I'm starting to see some logic in Matt's phrase quited above... :-)

You do not sound like an idiot.

But you have to twist your thinking around.

The curves are descriptions of what it takes to get an "average" reading.

The A curve is standard to measure to, as is the C curve.

If you measure 82dBSPL on the A curve and then simply switch to C curve the reading will be lower.

If you measure 82dBSPL on the A curve and then TURN up the volume of your playback system you can measure 82dBSPL on a C curve.

This is my very crude and uneducated synopsis: "A" curve describes how we hear content that is reproduced as "flat bandwidth"... "C" curve describes what it takes for us to hear content as "flat bandwidth" response.

I invite correction :-)

I think it is very good that people are thinking along the lines of what we call calibrated monitor gain. This is a big problem within our industry as there is no real calibrated monitor gain such as there is in the film industry.

Bob Katz in his great book (Chapter 15 for those who have it) on mastering talks about this and he says one should use band limited pink noise as the test. From 500 Hz to 2 Khz. As you can see fron the graphs above it wont make a lot of difference wether the A or C weighting is used.  (C weighting is suggested as the standard) He also suggests that 83 db is the figure to use. And you need to set each speaker separately. The level will go up about 3 db when both speakers are on. Another important point is knowing what the reference level is on your tracks, master buss etc. Mine is -15db FS at the moment but after reading Bob's book I am going to move the reference level down to -20db FS. So lets assume you have chosen -20db FS. Your band limited pink noise should be at -20 on the tracks and master output. If you have VU meters connected they should read 0 db VU.

You need to be able to mark your monitor gain somehow when you have done this. It is not a bad idea either to have a calibrated monitor gain control but that is maybe getting a bit detailed for this.

83db is a beautiful volume and you should get used to it. Also I have done mixes as low as 65 db as well for checking the critical balances of things and then back up to 83db for final checks. Loud bursts are also OK but not for long and you need to let your ears recover after a loud burst.

But this is great to see. If there was a defined standard to monitor gain many of the problems we have in modern production would go away such as the loudness wars.