-18 dBFS

[GuitarLegend]

While I am far from being a newbie I thought this question could best be answered here.

I have just come up on a mental blank and need some clarification. I understand that 1.23v = +4dBu = -18dBFS = 0dB VU and I don't have a problem with that. However, I have heard that some equipment is "calibrated to -18 dBFS" and my brain went into blank mode and I can't get out of that.

What do they mean by "calibrated to -18 dBFS"? Can you please make some sense of that?

 

[Chili]

You know, I'm not an expert on this, but FS means full scale. I am led to believe it isn't really dependent on a voltage or other calibrated unit. It's just whatever the software calculates for bit depth.... I think.

The voltage references are correct, but that is on the analog side. I kind of have the impression -18dBFS is after conversion; when the signal is in the digital realm. If it were to equal a certain voltage, it would have to be calibrated within the converter. Do manufacturers do that stuff?? Never heard of it before.

Sorry I can't be more useful. Hopefully, someone who knows will step up.

 

[GuitarLegend]

You know, I'm not an expert on this, but FS means full scale. I am led to believe it isn't really dependent on a voltage or other calibrated unit. It's just whatever the software calculates for bit depth.... I think.

The voltage references are correct, but that is on the analog side. I kind of have the impression -18dBFS is after conversion; when the signal is in the digital realm. If it were to equal a certain voltage, it would have to be calibrated within the converter. Do manufacturers do that stuff?? Never heard of it before.

Sorry I can't be more useful. Hopefully, someone who knows will step up.

Thanks, I know dBFS is full scale and is as loud as your equipment can play it. Its not an absolute level.

If audio equipment handles everything from -infinity to 0dBFS, I was just puzzled at what they mean when they say it is calibrated to any particular level. I cant make a connection with that statement

 

[Farview]

Not every converter is set so that line level equals -18dbfs. Some are -20dbfs, some are -16dbfs, old 16 bit converters tended to be calibrated to -12dbfs.

Some high end converters will let you change what line level will be on the digital side. In other words, you can calibrate the digital level that a given signal will be.

 

[GuitarLegend]

If I had to guess, I would say that the equipment is designed to consider 1.23v as being -18dBFS and would output the corresponding levels accordingly. They say some equipment is calibrated to -16dBFS which I cant begin to guess what level they are actually operating on. My guesses would get a bit wild and woolly

 

[GuitarLegend]

Not every converter is set so that line level equals -18dbfs. Some are -20dbfs, some are -16dbfs, old 16 bit converters tended to be calibrated to -12dbfs.

Some high end converters will let you change what line level will be on the digital side. In other words, you can calibrate the digital level that a given signal will be.

The fog is beginning to clear. I hate it when something doesn't gel in my head. Kind of makes you feel stupid. Just looking for a better understanding of this

 

[GuitarLegend]

Not every converter is set so that line level equals -18dbfs. Some are -20dbfs, some are -16dbfs, old 16 bit converters tended to be calibrated to -12dbfs.

Some high end converters will let you change what line level will be on the digital side. In other words, you can calibrate the digital level that a given signal will be.

Ah... so its really a converter thing. They take the incoming analog signal and convert it to digital according to some given reference level. When the analog signal is 1.23v they convert that to the appropriate digital value according to a set reference, eg -18dBFS? They could convert it to any level but that level is specified? That makes sense

 

[GuitarLegend]

Ok, a piece of equipment I have specifies:

"....dBFS Alignment +18dBu = 0dBFS (+22dBu at XLR output)..."

I think I understand now

 

[Farview]

Yes, the converters are set so that line level = something dbfs. That setting will differ, depending on what the manufacturer decided to calibrate it to. Or, like I said, high end converters will let you calibrate it yourself.

 

[GuitarLegend]

Yes, the converters are set so that line level = something dbfs. That setting will differ, depending on what the manufacturer decided to calibrate it to. Or, like I said, high end converters will let you calibrate it yourself.

Thanks, it all makes sense now. I knew it would be something simple but I wasn't thinking right

 

[Bobbsy]

Not every converter is set so that line level equals -18dbfs. Some are -20dbfs, some are -16dbfs, old 16 bit converters tended to be calibrated to -12dbfs.

Some high end converters will let you change what line level will be on the digital side. In other words, you can calibrate the digital level that a given signal will be.

^^^^^

This. As others have said, 0dB(FS) is simply the maximum level that can be encoded digitally...basically 111111111111111111111111 in a 24 bit recording.

The relationship between this and analogue levels is arbitrary: -18dB(FS)=0dBu is pretty normal but I've seen gear that's calibrated for -20 and even -22 (never -16 but I've just been lucky. I guess it's just like different quality analogue gear has more or less headroom about the 0dB reading on a meter.

As an aside, when I was working professionally, we had gear calibrated at -18, -20 and -22 but, in the end, we decided to standardise on -18 for everything and ignore any extra headroom. Headroom we had plenty of even at -18 but getting it wrong and sending too high a level into a piece of gear could have been expensive.

 

[GuitarLegend]

^^^^^

This. As others have said, 0dB(FS) is simply the maximum level that can be encoded digitally...basically 111111111111111111111111 in a 24 bit recording.

The relationship between this and analogue levels is arbitrary: -18dB(FS)=0dBu is pretty normal but I've seen gear that's calibrated for -20 and even -22 (never -16 but I've just been lucky. I guess it's just like different quality analogue gear has more or less headroom about the 0dB reading on a meter.

As an aside, when I was working professionally, we had gear calibrated at -18, -20 and -22 but, in the end, we decided to standardise on -18 for everything and ignore any extra headroom. Headroom we had plenty of even at -18 but getting it wrong and sending too high a level into a piece of gear could have been expensive.

Apparently, -18dBFS gives more than enough headroom for any application but I guess there must be a few exceptions

 

[Bobbsy]

Apparently, -18dBFS gives more than enough headroom for any application but I guess there must be a few exceptions

That was certainly our theory and it worked fine in practice. Some of the Sony Beta SX recorders we used were calibrated for +22 but we never encountered any programme material that needed the extra 4dB headroom. (And, by the time we transmitted by satellite, everything had to be compressed to blazes with no peaks about +8dBu which is why so much TV sound is so rubbish at home.)

 

[ecc83]

Yeah, bit of a head spinner!
I can forgive manfctrs of "lesser" AIs etc for not having the "pro" standard headroom of 20dB above +4dBu, around 12V rms since that would hardly be feasible at the price points and in any case, much other gear would be overdriven. They certainly could not do it with bus powered kit!

What DOES hiss me off however is that most of them cannot give us the basic information of what output level corresponds to -18dBFS (or any dBFS level they care to choose) When you think about it, a mic gain specc' of "55dB" means sod all! What we need is X mV in = Y,dBFS.

And just in case some of you misty eyed young'uns think things were simpler in the "Golden Age of Tape" BLODDY WASN'T! They had a different line up flux across The Pond and there were "nano Webers" and "milli Maxwells to contend with. (think Tesla got in there once? Old brain has lost SO much) Oh! And DOLBY level FFS!

BTW if ever you want a bunch of nice meters for free? Download the free Samplitude Pro X Silver. Goes to +10dBFS for some reason!
Dave.

 

[GuitarLegend]

BTW if ever you want a bunch of nice meters for free? Download the free Samplitude Pro X Silver. Goes to +10dBFS for some reason!
Dave.

I love the Blue Cat DP Meter Pro. I use that a lot. Some nice features there

 

[Bobbsy]

BTW if ever you want a bunch of nice meters for free? Download the free Samplitude Pro X Silver. Goes to +10dBFS for some reason!
Dave.

I've never played with Samplitude but I'm going to guess that Samplitude operates in 32 bit Floating Point which means that you can go above 0dB(FS) without clipping--even though you have to normalise downwards later to do anything with your file.

 

[Chili]

(And, by the time we transmitted by satellite, everything had to be compressed to blazes with no peaks about +8dBu which is why so much TV sound is so rubbish at home.)

Oh yeah... try watching football on the Fox network. Ear bleed.

 

[ashcat_lt]

What DOES hiss me off however is that most of them cannot give us the basic information of what output level corresponds to -18dBFS (or any dBFS level they care to choose) When you think about it, a mic gain specc' of "55dB" means sod all! What we need is X mV in = Y,dBFS.

What they will usually give you is a Nominal Level for the given input, along with either a maximum level or a "headroom" figure. The maximum level (like the nominal level) will be referenced - dbu, dbV, but the headroom usually isn't because it's relative to the nominal level. It's great fun when nominal is in dbu but maximum is dbV! (There's an app for that ) You can usually work it out from there. Or, like, run a calibrated test tone in and see where it sits.

 

[Massive Master]

In an ideal and perfect world, you want to record "oh, about where it's going to be in the mix" much of the time. If-18dBFS=0VU, even in a fairly crowded mix, you (A) should have a good amount of headroom at the analog stage and (B) won't have to bring all your faders down 15-20dB to start your mix. Same thing with the main buss. Assuming you have most of your stuff 6dB or so down from units (I know it varies, I'm just throwing incredibly rough numbers out) so your mix is running in the -18dB(FS)RMS range, you should have a decent amount of headroom there also - along with anything in the analog path if there is one.

For the record, I always tried to keep my tracking converters at -20 (as that's as low as they'd go if I recall), mix buss at -18 to -16 (depending on the converter - Some have much more "style" than others when being beaten on). Mastering converters are another story... The chain here is at -10. So when I'm beating the hell out of everything, the analog stuff is barely breathing. That means everything else needs recalibration to some extent also, but most mastering gear takes that into consideration or allows for easy tweaks -- The STC8M for example has a 10dB pad on the sidechain. Tracking, mixing, didn't need it. Mastering, couldn't possibly do without it although it was absolutely worthless for tracking or mixing.

S'all about happy voltage. Everything is spec'd at around 1-1.5V. Just because the circuit won't fail till 4 or 5V doesn't going to mean it's going to be happy about being smacked around at 3V all the time....