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Recording Level Meters ???

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Recording Level Meters ???

Postby DigitalMusicProduction » Wed Jan 27, 2021 3:25 pm

Hi

Being fairly new to music production in Logic Pro
I'm quite confused about the whole recording level metering layout, after spending time online from sites to video tutorials there's still no definitive answer as to what all the numbers actually mean?

Example, a level meter will start at 00dB and end at 6dB, while the opposite meter starts a 60dB and ends a 0dB, whilst the level fader itself will default at 12dB then rise to 9dB 3dB 6dB 0dB, the concept is baffling, could anyone explain? appreciated.
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Re: Recording Level Meters ???

Postby desmond » Wed Jan 27, 2021 3:28 pm

BTW I already replied to this where you posted this over on LogicProHelp...

Welcome to the world of engineering! There are many different metering standards and formats.

Logic uses "dBFS". 0dBFS is the highest level in a digital fixed point signal you can get. FS stands for Full Scale - ie the maximum level point.

(You can go above this *inside* Logic, but that's a complication that I'll skip over for now - let's just say that internally, pretty much all DAWs use floating-point number formats that can represent larger signals than this).

You do not want to to over 0dBFS on your master output, otherwise your mix will clip (have the top cutoff). -3dBFS, which is 3dB down from 0dBFS, gives you 3dB of headroom. You mixer channel in logic will be -infinity dBFS (that's *minus infinity*, complete silence, fader full down) all the way up to 0dBFS, the loudest a fixed point digital signal can go. (Logic can recognise when the internal floating point number representation of your digital signal goes over the fixed point number limits, so the meters actually go up to +6dBFS).

So, if you have a signal with a peak level of, say, -18dBFS, you can add 18dB of gain before your signal will reach the potential clipping point (reach the 0dBFS point).

Stuff like this is why some people prefer to stick to the music stuff, and let someone else worry about engineering standards! ;)
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Re: Recording Level Meters ???

Postby Hugh Robjohns » Wed Jan 27, 2021 3:49 pm

desmond wrote:You do not want to to over 0dBFS on your master output, otherwise your mix will clip (have the top cutoff)....

Minor point of order to avoid potential confusion.

It's not the mix that clips. As you rightly say, the floating point maths used in DAW software means the internal buses can run hotter than 0dBFS without issue.

The limiting factor is the digital connection from the DAW and/or the D-A converter used to monitor the output signals. These are 'fixed-point' devices that have a defined maximum output level of 0dBFS.

So when mixing and mastering it is necessary to keep signals below 0dBFS to avoid overloading the replay side of the signal chain.
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Re: Recording Level Meters ???

Postby desmond » Wed Jan 27, 2021 4:04 pm

Hugh Robjohns wrote:The limiting factor is the digital connection from the DAW and/or the D-A converter used to monitor the output signals. These are 'fixed-point' devices that have a defined maximum output level of 0dBFS.

So when mixing and mastering it is necessary to keep signals below 0dBFS to avoid overloading the replay side of the signal chain.

Indeed. For the OP though, it was a brevity, ie the "mix" being the audio that you are hearing or rendering to your mix file, and I don't think it was misleading. Basically, (as we know), the "mix" which is coming out of Logic to either your interface (to hear), or your bounce file (to save), is a fixed-point format, and it's important for your "mix" not to go over 0dBFS, as the "mix" (what you are hearing or rendering to a file) can clip.

Note: In actual fact, in Logic (from memory), if you go over 0dBFS at the master output, it doesn't actually hard clip in the way you expect due to running out of headroom - there seems to be some soft (ie invisible) safety limiter thing going on, likely as a way to help protect the output chain from distortion. But the principle remains the same, anyway. :thumbup:

Plus: Bear in mind I wrote that on a forum that doesn't have a resident "Hugh" ;)
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Re: Recording Level Meters ???

Postby DigitalMusicProduction » Wed Jan 27, 2021 7:56 pm

Yes I'm aware of various recording input levels being best recommended at -20dB to -15dB / -18dB to -12dB with various optimal peaks levels no higher then +9dB to +6dB to facilitate sufficient headroom for mastering, and the core principle being not to exceed 0dB thus to avoid clipping, all this i understand, my question is about the numerical confusion on both sides of the faders.

Example why is the instrument channel strip fader in Logics inspector set to (Unity Gain) by default representing 0dB? when at the same time it has a value of -12dB, then at the top of the fader there is second 0dB representing the max output? (clipping) also the baffling concept relating to the faders being the lower the numbers the higher the sound, and the higher the numbers the lower the sound?

This is obviously a system systematically correct in its own entirety, the only thing is i don't understand it, and the majority of Google searches and YouTube tutorials are not explaining the concept.
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Re: Recording Level Meters ???

Postby desmond » Wed Jan 27, 2021 8:21 pm

DigitalMusicProduction wrote:Example why is the instrument channel strip fader in Logics inspector set to (Unity Gain) by default representing 0dB?

Unity gain, a fader set at unity gain means "apply no gain change to the signal" - ie, "change the signal by 0dB" (Note the difference between a relative 0dB change, versus an absolute 0dBFS maximum level - two different things.). Whatever absolute level the signal is will not be changed.

DigitalMusicProduction wrote:when at the same time it has a value of -12dB, then at the top of the fader there is second 0dB representing the max output? (clipping) also the baffling concept relating to the faders being the lower the numbers the higher the sound, and the higher the numbers the lower the sound?

Remember, the signal at it's lowest is in minus figures (minus infinity -> -96dBFS -> -48dBFS etc up to 0dBFS.)

0dBFS is a scale with absolute values. A 6dB change is a relative value, so you could have a signal peaking at -12dBFS, and you add +6dB of gain, so the signal now peaks at -6dBFS (6dB louder).
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Re: Recording Level Meters ???

Postby CS70 » Wed Jan 27, 2021 8:40 pm

DigitalMusicProduction wrote:Example why is the instrument channel strip fader in Logics inspector set to (Unity Gain) by default representing 0dB? when at the same time it has a value of -12dB, then at the top of the fader there is second 0dB representing the max output? (clipping) also the baffling concept relating to the faders being the lower the numbers the higher the sound, and the higher the numbers the lower the sound?

The reason for levels going from 0 to negative values is because a fader is just another form of a volume knob, and volume knobs are attenuators. They can't increase a voltage level, but can decrease it. This in opposition to gain devices - amplifiers - that can increase a signal amplitude.

So the starting point is the max voltage level of the power amplifier. That is the reference level, the "zero".

From this level, you can attenuate: how much are you subtracting from the maximum possible output? 5dB? 10dB? Then it's 0 -5 or 0 - 10... which is abbreviated to -5 or -10 because the 0 is always the same.
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Re: Recording Level Meters ???

Postby RichardT » Wed Jan 27, 2021 8:45 pm

DigitalMusicProduction wrote:Yes I'm aware of various recording input levels being best recommended at -20dB to -15dB / -18dB to -12dB with various optimal peaks levels no higher then +9dB to +6dB to facilitate sufficient headroom for mastering, and the core principle being not to exceed 0dB thus to avoid clipping, all this i understand, my question is about the numerical confusion on both sides of the faders.

Example why is the instrument channel strip fader in Logics inspector set to (Unity Gain) by default representing 0dB? when at the same time it has a value of -12dB, then at the top of the fader there is second 0dB representing the max output? (clipping) also the baffling concept relating to the faders being the lower the numbers the higher the sound, and the higher the numbers the lower the sound?

This is obviously a system systematically correct in its own entirety, the only thing is i don't understand it, and the majority of Google searches and YouTube tutorials are not explaining the concept.

Yes it is confusing!

The fader level in dB shows how much the fader is amplifying the incoming signal. 0 dB represents no change to the signal, +3dB means that the fader is increasing the signal by a certain amount, -3dB that it is reducing the signal by a certain amount.

The meter level shows the output level. If you move to fader to +3dB, then you’ll see the output level go up by 3dB.

The negative values take some getting used to! 0dBFS is the highest level of signal you can send to your audio interface without digital clipping, and all the other vales are related to that. So -10dBFS is lower than the maximum level, and -20dBFS is even lower. The numbers are going up, but because there is a minus sign, they represent lower levels.
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Re: Recording Level Meters ???

Postby Hugh Robjohns » Wed Jan 27, 2021 9:25 pm

DigitalMusicProduction wrote:...my question is about the numerical confusion on both sides of the faders.

Example why is the instrument channel strip fader in Logics inspector set to (Unity Gain) by default representing 0dB? when at the same time it has a value of -12dB, then at the top of the fader there is second 0dB representing the max output?

Are you possibly confusing the scale alongside the channel meter, which has 0dBFS at the top, with the channel fader which just happens to be placed such that it's unity level roughly sits opposite the meter's -12dBFS mark?

...the baffling concept relating to the faders being the lower the numbers the higher the sound, and the higher the numbers the lower the sound?

Not sure where you got that idea from. Faders adjust signal level above or below a nominal reference level. It's measured in decibels, with the reference point -- unity gain, or 'no change' being devoted as 0dB. To make things louder you raise the fader, denoted by positive decibel values. For example, +6dB doubles the signal amplitude, and +12dB quadruples it.

Pulling the fader below 0dB attenuates the signal, denoted by minus numbers. So -6dB halves the signal amplitude.

...the only thing is i don't understand it, and the majority of Google searches and YouTube tutorials are not explaining the concept.

This is a familiar theme in your posts, where you've generally been persuing quite advanced techniques and ideas, but without a solid foundation of knowledge.

I would strongly recommend some reading up of the basics. Mike Senior has written a couple of very good books which are easy to follow and explain things like metering, gain strictures, mic techniques and more very clearly. Yo could do a lot worse than investing your cash and time to study them.
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Re: Recording Level Meters ???

Postby merlyn » Thu Jan 28, 2021 3:02 pm

To add to what has been said above I understand dB from a maths angle. Using dB allows multiplication to be replaced with addition.

I've noticed 0dB can be a sticking point. 0dB means multiply by 1.

This is because dB are to do with powers of a number and any number to the power of 0 is 1. Kind of counterintuitive maybe, but mathematically correct :

x^0 = 1

Positive powers of a number make the number bigger :

2^2 = 4

and negative powers of a number make the number smaller :

2^-1 = 0.5

so positive dB mean the signal is getting bigger (has a higher amplitude) and negative dB mean the signal is getting smaller (has a lower amplitude).

You will also see -infdB which means -infinity dB and this corresponds to an amplitude of 0.
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Re: Recording Level Meters ???

Postby DigitalMusicProduction » Thu Jan 28, 2021 3:11 pm

desmond wrote:Unity gain, a fader set at unity gain means "apply no gain change to the signal" - ie, "change the signal by 0dB" (Note the difference between a relative 0dB change, versus an absolute 0dBFS maximum level - two different things.). Whatever absolute level the signal is will not be changed

When you mention Unity gain at 0dB are you referring to the volume fader which is also set between 12dB and 15dB, thus anything above or below this point will be +dB or -dB ? Is this also referred to as the floating point ?
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Re: Recording Level Meters ???

Postby desmond » Thu Jan 28, 2021 3:23 pm

DigitalMusicProduction wrote:When you mention Unity gain at 0dB are you referring to the volume fader which is also set between 12dB and 15dB, thus anything above or below this point will be +dB or -dB ?

When the fader is at it's "0" mark, it indicates zero gain change. The signal passing through that channel will not have it's volume *altered* by the fader at all.

If you bring the fader down by 3dB, then the signal passing through that channel will have it's volume reduced by 3dB, so the signal will be made 3dB quieter.

Same for if you raise the fader to +3dB (3dB above the zero mark on the fader) - you are turning the signal up by 3dB, so it will now be 3dB louder than what it was before.

DigitalMusicProduction wrote:Is this also referred to as the floating point ?

No. Given where you are, you probably don't want to get into the details of floating point numbers. ;)

Edit: To be clear, the numbers on the *fader* indicate how much dB to increase or decrease the volume level of the audio signal. 0 means "don't change it", +3 means "increase it by 3dB" etc.

The numbers on the *meter* indicate, in dBFS, the *level* (volume) of the signal going through the audio channel.

As you increase or decrease the fader, the signal's volume level gets changed accordingly, and you see the signal get louder or quieter on the meters accordingly.
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Re: Recording Level Meters ???

Postby DigitalMusicProduction » Thu Jan 28, 2021 6:05 pm

desmond wrote:0 means "don't change it"

Why then is the're an option to increase above 0dB upwards of +9dB +6 +3 if the Unity gain is not ment to be changed ?
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Re: Recording Level Meters ???

Postby desmond » Thu Jan 28, 2021 6:11 pm

DigitalMusicProduction wrote:Why then is the're an option to increase above 0dB upwards of +9dB +6 +3 if the Unity gain is not ment to be changed ?

??

The fader is there for you to turn your signal up or down. That's a fundamental part of mixing. I don't understand why/where you equated unity gain with "not meant to be changed". If it was "not meant to be changed" they wouldn't specifically put a fader on there, a control expressly intended for the purpose of changing the levels.
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