The Logic Off Topic list

Roger of litepipe fame said:

>I'm trying to get the handle on VU and PPG meters.
Me too!!

>... there are a few things that puzzle me....
Me too!!

>For instance I set my meters so that -14dbfs reads 0dbfs on the VU which 
>they kept referencing in the tutorial. Now when I master to 0dbfs on the 
>VU meter it seems so weak on the Logic meter.
OK.
Well
... nobody else is saying anything, so here goes with the little I know.

VU and dBfs are not necessarily that compatible from what I understand. The 
way I read it, it's the self-same issue of peak versus RMS that keeps 
coming up time and time again.

The way I read the situation is that dBfs is more common in digital 
applications. dBfs (decibel full-scale) tries to tell you how far your 
reading is at the moment from full scale, with full scale referring to the 
maximum level that your ADC (analog-to-digital-converter) can convert.

If your 'normal operating level' is -14 dBfs, then you've got +14 dB of 
headroom before your ADC goes AWOL or whatever. Different places work to 
different levels, but that's basically what it means. I think!!

Digital and analogue meters are usually calibrated to provide as a high 
resolution as possible near the chosen operating level. As the level goes 
higher than this, so does the resolution drop. So ... when you're near 
operating level then one unit on your display may well properly represent 
one dB. Unfortunately, that's likely to be the only place you get that 
representation. One unit at say -50 could be 8 dB or 10 db or 15 db or a 
bit more than that even different.

VU's and PPM's do much the same thing as each other (Volume Metre displays 
and Peak Program Metre Displays). VU displays show you average volume 
levels while PPM's, of course, show peaks. So ... if you're displaying a 
sine wave then you're probably showing a difference of about 3dB between 
them. Can be as much as 12. Technically, the difference between these two 
is called the 'crest factor'.

You've also got a difference in response time to contend with. A VU metre 
can take 3/10ths of a second to stabilize its response to a 1 kHz tone, 
whereas a PPM meter can do so in less than 1/100th of a second. Given the 
crest factor and these differences in the 'ballistics' o the two methods, 
the two kinds of meters always respond to audio differently.

Basically, VU meters, which work on average levels, are designed to more 
closely mimic the human ear. However, it's very bad at dealing with peaks 
because of its inordinately slow response time. The average VU meter shows 
you a peak signal some 8 to 20 dB below its actual value.

When a VU meter gives you a zero reading, then all you're seeing is the 
"normal operating level" chosen by that particular set up which is pretty 
random. It could be -10 dBm. It could be 0 dBm. It could be anything, 
really. (A dBm is the power dissipation of 1 mW into a resistor loaded with 
600 ohms).

The VU meter is simply calibrated so that something or other registers a 
zero, and you usually need to have some other way of telling what that zero is.

>How do all of you have it set up? What levels do you master to? What is 
>the induatry standard? Is it 0dbfs on a VU calibrated to read 0dbfs at 
>-14dbfs?

Basically, I don't think there IS an industry standard per se because each 
recording facility can set what it likes as its own reference for zero. 
However, that said I think that -14 and -18 are both pretty common. I think 
the idea here is that need to find out what's been decided and done so that 
you know what you're doing from that point on.

>What I do is put a Vintage Meter on the Master Output when I'm mastering a 
>song to see the volume.
Don't think you can do much better than that, to be honest!!

>I want to make sure I'm somewhere in the ballpark.
Use your ears? If you hear a hot dog vendor you're at the right ballgame. 
If not, check your calendar (just kidding!!)

>I'm going to pull a few songs from c.d. and compare the levels.
Best way to go. If you want them to match, then you'll have to do it by hand.

>I was just wondering if anyone here could give me a little more insight:-)
Sorry. Got no insight to shed. I really don't know much and I was hoping 
someone would answer your question but basically everyone seems to be 
ignoring it.

Which is a pity, really. C'mon guys ... where ARE you all??!!!

>Thanks in advance:-))
Ditto

Kool Musick
Keep Musick Kool


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