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Does Out 1 (Main) effect anything other than volume?

moerker

Inspired
So, after reading all of this, am I right if I conclude that
  1. One may consider matching the VU meter with an DAW meter needs a specific, reliable, easy setup, therefore using shunts only.
  2. Matching the VU meter with the DAW using Out1 to increase SNR, since the Pre-Amplifiers in an interface shall run at a gain of 1 for best results.
  3. If so, this doesn't necessarily apply to "wet" presets, because of the amplification added by the blocks.
But, let's say the preamp of an interface reaches unity at a specific location, therefore allows to also attenaute the signal, attenuation on preamp amplifier side won't degrade the signal, since no noise from connecting the AX8 to the interface will be amplified.

Am I right here?
 

chris

Legend!
All I know is that I hear no added noise or issue with the Output knob at any position lower than maximum, and that it is not a requirement to turn the Out knob to maximum.
 

Dave76

Inspired
This is assuming that the VU meter and the meter in every DAW and 0 on every audio interface is exactly the same, right? Is that a standard they all meet?
Yes, there are standards governing this. You'd have to be familiar with your specific audio interface, DAW, etc. to ensure that the specific standards they use and their current configuration match. There are all sorts of variations in terms of peaks vs. RMS vs. hold time vs. offsets that can make it difficult to reliably compare meters if you aren't familiar with what they are displaying.

However, in the digital realm, dBFS is pretty ubiquitous because 0 dBFS is the max signal possible without clipping so typically 0 on meters and the clip indicators on audio interfaces, in DAWs, etc. will be calibrated to 0 dBFS making that a pretty reliable reference point. Once you start tickling the red on an audio interface or in a DAW, you are probably hitting 0 dBFS meaning you are exceeding the maximum value that the sample format can support. Some interfaces and DAW may give you some wiggle room where they trigger the clip indicator a few dB early just because that's behavior that people coming from the analog world are used to working. Again, you need to check the manuals.
 

Dave76

Inspired
From this I gather that Unity Gain just simply isn’t the correct term to use in all this? That’s why you mentioned “level matching”?
Correct.
With all due respect, that is not correct. The concepts of "gain" and "unity gain" have very precious definitions that come from the discipline of electronics. The existence of electric guitars or the physical boundaries of devices like the AX8, mixers, etc. do not factor into these definitions.
 

Rex

Legend!
So, after reading all of this, am I right if I conclude that
  1. One may consider matching the VU meter with an DAW meter needs a specific, reliable, easy setup, therefore using shunts only.
Matching the VU meter to the meter in the DAW benefits from a specific, reliable, easy setup, but doesn’t require that. Shunts have nothing to do with that.


Matching the VU meter with the DAW using Out1 to increase SNR, since the Pre-Amplifiers in an interface shall run at a gain of 1 for best results.
Yes, in theory. In practice, the noise generated by your guitar itself will be much greater than the noise generated by imperfect levels in your DAW or interface.



If so, this doesn't necessarily apply to "wet" presets, because of the amplification added by the blocks.
“Wet” doesn’t matter. The Amp block is the source of most of your gain.
 
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chris

Legend!
With all due respect, that is not correct. The concepts of "gain" and "unity gain" have very precious definitions that come from the discipline of electronics. The existence of electric guitars or the physical boundaries of devices like the AX8, mixers, etc. do not factor into these definitions.
But that’s exactly my point - the AX8 doesn’t change the definition of Unity Gain, therefore the term shouldn’t be used to describe “the AX8 with out 1 set to max.”
 

Rex

Legend!
The concepts of "gain" and "unity gain" have very precious definitions that come from the discipline of electronics..
They do indeed. Gain is output level or power compared to input level or power.

But let's say you have a 100 milliwatt signal that you then convert to a digital signal. How many watts is that digital signal? It's undefined. You can't run a gain calculation with undefined numbers. The best you can do is to choose a reference in the digital domain and compare it to a chosen reference in the analog domain.
 

Smittefar

Fractal Fanatic
It is quite well-defined how to convert a digital level to an analog level (a voltage) or vice versa. AD and DA converters don't have random references. But it is almost always voltages not power that are converted.
 

Rex

Legend!
It is quite well-defined how to convert a digital level to an analog level (a voltage) or vice versa. AD and DA converters don't have random references. But it is almost always voltages not power that are converted.
Can you point me to a reference for that standard?
 

Rex

Legend!
0 DBFS becomes +4 dBu
This isn’t unity gain, it’s level matching (approximate level matching at best, because it attempts to equate a peak level to an average level).


The following is lifted from Sengpiel Audio’s website. Despite the imperfect translation from German, its meaning is clear, and its explanation is better than the one I wrote.

There is no decibel to dBFS converter

Notice - Comparing dBu and dBFS: There is really no fixed world standard like e.g. −20 dBFS = +4 dBu = 0dBVU. The digital peak scale is not equivalent to the analog RMS scale.

You can never match dBFS and dBu.


Analog audio: positive and negative voltage. dBFS is in contrast a binary number.
Digital audio: zeroes and ones.


There is no such thing as peak volts dBu *). It is incorrect to state peak voltage levels in dBu.


Never take the following funny guessing game for granted. Use it only as a rough guide:
European & UK calibration for Post & Film is −18 dBFS = 0 VU = +4 dBu

BBC spec: −18 dBFS = PPM "4" = 0 dBu
American Post: −20 dBFS = 0 VU = +4 dBu
Orchestral −18 dBFS = 0 VU = +4 dBu
Rock and / or Radio −16, or −14, or −12 dBFS = 0 VU = +4 dBu
Digi 002 is only capable of −14 dBFS.
German ARD & studio PPM +6 dBu = −10 (−9) dBFS. +16 (+15) dBu = 0 dBFS. No VU.
EBU R68-2000 - The European Broadcasting Union recommends: digital level
−9 dBFs (maximum). You have to keep the upper 9 dBs empty without any use.
The reference level is −18 dBFs. 0 dBFs is equal to +15 dBu.

 

Smittefar

Fractal Fanatic
No, the the reference voltage is calculated from a power and resistor based on the definition of dBu. dBu is a voltage standard. The 'u' means that it is an unloaded signal. No load means no current and hence no power. All voltages can be represented by a dBu value. An ADC converts sample values, it does not make means.
 
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Rex

Legend!
dBu is a voltage standard.
Agreed.


All audio signals can be split into a sum of sine waves...
Steady-state signals, yes. But guitar signals aren't steady-state.


...so even if it was true only for sine waves, it would still be true for audio signals
It's not, though. A sine wave has a fixed and constant ratio of peak-to-RMS. A spiky signal has a lower peak-to-RMS ratio. And a square wave has no difference between peak and RMS level.

All this is complicated by the fact that there is no universal standard for representing 0 VU in the digital domain, as seen in post #51 above.


The definition of gain itself breaks down at digital boundaries, because a voltage at the input of an A/D converter gets converted to a string of bits, with no voltage involved other than the voltage of the 1's and 0's , which remain constant no matter how much signal you preset to the converter.


Curiously, it is possible to define gain for a digital network sandwiched between to converters. In such a system, gain is defined as the ratio of signal going out of the D/A converter to the signal coming into the A/D converter.
 

Smittefar

Fractal Fanatic
I edited the part of summing sine signals, because it was wrong.

The fact is that if you take a digital signal and output it through a +4dBu DAC and input it through any +4dBu ADC you get the same digital levels in both ends of the chain. This is only possible because the analog signal levels between the two converters are well-defined.
 
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Rex

Legend!
The fact is that if you take a digital signal and output it through a +4dBu DAC and input it through any +4dBu ADC you get the same digital levels in both ends of the chain. This is only possible because the analog signal levels between the two converters are well-defined.
And here, we’ve reached a point of agreement. :)
 

Dave76

Inspired
But that’s exactly my point - the AX8 doesn’t change the definition of Unity Gain, therefore the term shouldn’t be used to describe “the AX8 with out 1 set to max.”
I don't understand what you are saying here. Do you acknowledge that "level" is something that can be measured in a multitude of spots in a signal chain? Well, if so, "gain" is simply the ratio of output to input between any combination of two of those points where the signal is meaningfully correlated. If you can measure levels in multiple spots, you can calculate gain across different parts of the signal path as well. In any case where you can calculate gain, "unity gain" is the point where the result of the calculation is 1. Because it can be calculated across different spots, when someone says "gain" or "unity gain", they can mean many different things.

The only point I'm trying to make here, that I've repeated a few times, is that OUT1 set to max is the ideal starting point whether we are talking about using the AX8 in front of an amp or plugging into a mixer or audio interface. If you are in a situation where that isn't working, absolutely feel free to lower the level, but I'd also urge you to try figure out why you have to lower the level in the first place -- particularly if you are lowering it below around the halfway point. I don't think this guidance is too difficult for either a beginner or experienced musician to follow.
 

chris

Legend!
OUT1 set to max is the ideal starting point whether we are talking about using the AX8 in front of an amp or plugging into a mixer or audio interface.
i'm saying that some people refer to that as "Unity Gain." is it accurate to call it that? (actually asking)

I'd also urge you to try figure out why you have to lower the level in the first place ... I don't think this guidance is too difficult for either a beginner or experienced musician to follow.
unfortunately this is difficult for many because they have little to no experience with audio. many come from a guitar-amp-only background where they don't have to worry about any of this. so when they are told to "turn out 1 all the way up" they tend to just stick to this. then they go to a gig where the sound engineer won't reduce their channel gain (for whatever reason) and there is a huge problem. this has been documented countless times by now, and i'm just saying it's a reality.

almost everyone who does suggest "turn out 1 to 100%" eventually also says "but if it's an issue then just turn down" but most people only read the beginning and go with the 100% thing as a hard rule.

i'm also saying that i and many others have never experienced detrimental (or any) added noise from running the out knob lower than 100%. so i like to offer that option to new users rather than a wall of "turn the knob all the way up."

i just think this boils down to "most ideal" vs "most practical" methods. i think these 2 concepts are always at odds with each other in any industry.
 

Rex

Legend!
..."gain" is simply the ratio of output to input between any combination of two of those points where the signal is meaningfully correlated. If you can measure levels in multiple spots, you can calculate gain across different parts of the signal path as well. In any case where you can calculate gain, "unity gain" is the point where the result of the calculation is 1.
You're right. Gain can be calculated across any two analog points in the signal chain. And it can be calculated at any two points within a single digital device. And "unity gain" means a gain of 1 (which equals 0 dB).

The first danger is saying that turning Out1 all the way up will give you unity gain. That only gives you unity gain across the volume pot (because that's how volume pots work). But it's not unity gain for the entire AX8. The volume pot is just one of its components. There are other sources of gain — both positive and negative gain — within the AX8. The advantage of diming Out1 is that, if you're connected via S/PDIF and if you're running into a DAW, 0 VU on the AX8 gives you close to 0 VU in most DAWs. That's a convenience — if you're using a DAW.

The second danger is saying that turning Out1 all the way up is the best starting point. Sure, it gives you the best signal-to-noise ratio — in one component (the AX8). But, in all but the most extreme situations, that noise reduction cannot be heard by human ears because it's masked by much stronger sources of noise (like your guitar, for instance). It's an inaudible improvement. And that makes it less important than anything else which might audibly improve the audience or guitarist experience.

If the sound guy can't or won't cut the gain on your channel... if you share responsibility for house levels, and you find out halfway through the first song that you need more volume to FOH... if you don't get to run through the PA at all... these are all reasons why it will be better to start out with Out1 below maximum. Turning down Out1 will make an audible improvement in the sound, and that overrules any inaudible change.



...when they are told to "turn out 1 all the way up" they tend to just stick to this. then they go to a gig where the sound engineer won't reduce their channel gain (for whatever reason) and there is a huge problem. this has been documented countless times by now, and i'm just saying it's a reality.
This. Much trouble and frustration has been documented here when people read that maxing Out1 is the "best thing to do." And @chris is right: many people are tuning out this discussion because it's "geek talk" that's outside their comfort zone. They're just waiting for the final takeaway: "Just tell me what to do."
 
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