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Simple calibration of recording equipment
Old 12th September 2012
  #1
Gear Head
 
🎧 10 years
Simple calibration of recording equipment

Hi

I know there are lots of threads on the subject of calibrating your recording equipment, but I would like to describe my setup and ask for some opinions.
I have a mic pre, going to a Focusrite sapphire pro 40 going into Pro tools and outputting to an M series Soundcraft analogue mixer.

Would I be correct in thinking that a simple way to calibrate all this would be as follows. Generate a test tone that goes into the mic pre, set the input of the mic pre to optimum level (ie occasionally peaking), then set a similar input level on the Focusrite and Pro tools, and then finally the Mixer, that way all is operating at optimum level.

Lastly what would be the best and reliable equipment (low cost preferably) to generate the test tone, some kind of hardware or software tone generator? and what signal should I use, a sine 1Hz test tone?

Thanks

R
Old 12th September 2012
  #2
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jrhager84's Avatar
 
🎧 10 years
A test tone CD is nice because it has different frequencies at different levels, as well as pink noise.

Sent from my SAMSUNG-SGH-I777
Old 12th September 2012
  #3
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mexicola's Avatar
 
🎧 10 years
What exactly are you trying to calibrate?

Individual pieces of gear sometimes have calibration trimpots that are accessible internally, but you'll need the schematic or an owner's manual to know which trimpot does what and to know what signal level to send into the unit. And sometimes - for example with an 1176 - you must calibrate the trimpots in a certain order and then repeat certain steps to insure proper calibration.

Your description of a "calibration" doesn't seem to make much sense. It just sounds like you're wanting to run a sine wave through your gear for no apparent purpose.

Also, a 1Hz test tone would be inaudible. Hopefully that's a typo and you meant 1kHz.
Old 12th September 2012
  #4
Gear Head
 
🎧 10 years
Hi thanks for your comment

Maybe calibration is the wrong term. All I want to do is lineup all my gear so everything is peaking roughly at the same point in order to get a better quality recording
Old 12th September 2012 | Show parent
  #5
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bogosort's Avatar
 
🎧 10 years
Quote:
Originally Posted by rifkijones ➑️
Maybe calibration is the wrong term. All I want to do is lineup all my gear so everything is peaking roughly at the same point in order to get a better quality recording
Hi, what you mean is gain staging -- configuring the input and output levels on your devices optimally, for whatever definition of "optimal" you might have. The usual goal is to maximize signal-to-noise ratio through the entire signal path.

Most professional devices were designed to work with nominal signal levels of +4 dBu at their inputs and outputs, though some may sound better when hit harder or softer (so experiment!). How do you ensure you're sending +4 dBu to each piece of gear? If you're using a DAW, first figure out the maximum output your interface can muster, i.e., what 0 dBFS means on your particular interface, and for that you'll have to read the manual. For the sake of example, let's say you discover that the max output is +22 dBu; this means that you have 18 dB of headroom between max output and the nominal signal level (22 - 4 = 18), so if you instantiate a signal generator plug-in with a 1 kHz sine wave at -18 dBFS RMS, you should have +4 dBu on the analog output of the interface. (If that's not entirely clear, read it over again until it is; remember, the difference between 0 dBFS and -18 dBFS in the digital realm is the same as the difference between +22 dBu to +4 dBu in the analog domain).

So you've set up a signal generator in your DAW (ensure it's in RMS and not peak mode); how can you tell if you're really getting +4 dBu at the analog output? Plug an appropriate cable into your interface's output (or into the patchbay's output), take out your voltmeter, and measure it directly (if you don't have a voltmeter, definitely buy one; full-featured multimeters cost less than $20 these days). Put the meter in AC RMS mode and, if it's a TRS connector, place one probe on the tip and one on the ring; if it's XLR, a probe on pin 2 and a probe on pin 3. Your meter should read 1.23 VAC RMS, or something very close to it.

Once you're satisfied that you have +4 dBu coming out of your interface, patch it into your various analog devices. Then measure the output of that device with a multimeter in the same way as before, tweaking the device's gain knob(s) and/or fader(s) until you see 1.23 V on the output. If the device has multiple gain stages, each should be set close to its nominal, 0 dB position. Any VU meters on the device calibrated to +4 dBu should be showing 0. Bypass the signal generator and run music through the signal path -- how does it sound? If it sounds distorted or otherwise crappy, the device is likely expecting -10 dBV signals (some can be switched between -10 dBV and +4 dBu, but if not, you'll have to lower the output of whatever's in front of it to about -0.3 V.) Or maybe music through the device sounds fine, but when you lower the input and raise the output it sounds even better!

Do the same for all your devices, experimenting with different input and output levels, and soon you'll have your equipment gain-staged properly, your confidence will be higher, and women will find you more attractive.

Edit: for mic inputs on preamps, there's no such thing as nominal levels -- it depends too much on the source and microphone. Shoot for roughly the same levels in your DAW's meters as line-level signals.
Old 12th September 2012
  #6
Gear Maniac
 
🎧 10 years
mic pre dist

Quote:
Originally Posted by rifkijones ➑️
Hi

<snip>

Would I be correct in thinking that a simple way to calibrate all this would be as follows. Generate a test tone that goes into the mic pre, set the input of the mic pre to optimum level (ie occasionally peaking), then set a similar input level on the Focusrite and Pro tools, and then finally the Mixer, that way all is operating at optimum level.
-----------------------------------
I don't recommend running line level tones through the mic pre.
also check and make sure you can by pass the mic pre on the focusrite
avoid mic pre into mic pre
start with line level 1k tones dial in the board.
C
----------------------------------

Thanks

R
Old 13th September 2012 | Show parent
  #7
Lives for gear
 
mexicola's Avatar
 
🎧 10 years
Quote:
Originally Posted by rifkijones ➑️
Hi thanks for your comment

Maybe calibration is the wrong term. All I want to do is lineup all my gear so everything is peaking roughly at the same point in order to get a better quality recording
Well, different gear will peak at different levels. Professional gear is designed to run nominally at +4dBu, but how much you can go over that before clipping occurs depends on the piece of gear itself. And just because it clips at a certain point, that has ABSOLUTELY NO bearing on the sonic "perfectness" at that point.
The best thing to do is to use your ears and adjust accordingly to get the best sound for each individual source you record. Yes, this means adjusting knobs every time you set up to record something new. Does this seem like a lot of work to actually listen to each source and adjust accordingly? This is why professional engineers get paid - because they use their ears and adjust accordingly; because their WORKING. There is no "golden setting" that you can put the knobs at and expect perfection every time.
I think what you're trying to do will have no bearing on the quality of your recordings, because what you're trying to do is completely superfluous. Stop using your eyes to record.
Old 14th September 2012 | Show parent
  #8
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bogosort's Avatar
 
🎧 10 years
Quote:
Originally Posted by mexicola ➑️
I think what you're trying to do will have no bearing on the quality of your recordings, because what you're trying to do is completely superfluous. Stop using your eyes to record.
That's rather harsh, isn't it? Unless I'm misinterpreting the OP, he's trying to learn how to gain-stage his equipment, which indeed will help with the quality of his recordings. And what's wrong with looking at meters? Do you not use meters when setting levels for tracking?
Old 14th September 2012 | Show parent
  #9
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MixedSignals's Avatar
 
2 Reviews written
🎧 10 years
Quote:
Originally Posted by bogosort ➑️
That's rather harsh, isn't it? Unless I'm misinterpreting the OP, he's trying to learn how to gain-stage his equipment, which indeed will help with the quality of his recordings. And what's wrong with looking at meters? Do you not use meters when setting levels for tracking?
actually the only meters i look at are the master out to ensure i am not clipping
Old 14th September 2012
  #10
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e-are's Avatar
 
🎧 15 years
Quote:
Originally Posted by bogosort ➑️
That's rather harsh, isn't it? Unless I'm misinterpreting the OP, he's trying to learn how to gain-stage his equipment, which indeed will help with the quality of his recordings. And what's wrong with looking at meters? Do you not use meters when setting levels for tracking?
Both of his replies were a lil harsh. The op is asking a simple gain staging question that is not a bad question. I think it has been answered now.

Sent from my SPH-D710
Old 20th June 2015
  #11
Here for the gear
 
🎧 5 years
Quote:
Originally Posted by bogosort ➑️
Quote:
Originally Posted by rifkijones ➑️
Maybe calibration is the wrong term. All I want to do is lineup all my gear so everything is peaking roughly at the same point in order to get a better quality recording
Hi, what you mean is gain staging -- configuring the input and output levels on your devices optimally, for whatever definition of "optimal" you might have. The usual goal is to maximize signal-to-noise ratio through the entire signal path.

Most professional devices were designed to work with nominal signal levels of +4 dBu at their inputs and outputs, though some may sound better when hit harder or softer (so experiment!). How do you ensure you're sending +4 dBu to each piece of gear? If you're using a DAW, first figure out the maximum output your interface can muster, i.e., what 0 dBFS means on your particular interface, and for that you'll have to read the manual. For the sake of example, let's say you discover that the max output is +22 dBu; this means that you have 18 dB of headroom between max output and the nominal signal level (22 - 4 = 18), so if you instantiate a signal generator plug-in with a 1 kHz sine wave at -18 dBFS RMS, you should have +4 dBu on the analog output of the interface. (If that's not entirely clear, read it over again until it is; remember, the difference between 0 dBFS and -18 dBFS in the digital realm is the same as the difference between +22 dBu to +4 dBu in the analog domain).

So you've set up a signal generator in your DAW (ensure it's in RMS and not peak mode); how can you tell if you're really getting +4 dBu at the analog output? Plug an appropriate cable into your interface's output (or into the patchbay's output), take out your voltmeter, and measure it directly (if you don't have a voltmeter, definitely buy one; full-featured multimeters cost less than $20 these days). Put the meter in AC RMS mode and, if it's a TRS connector, place one probe on the tip and one on the ring; if it's XLR, a probe on pin 2 and a probe on pin 3. Your meter should read 1.23 VAC RMS, or something very close to it.

Once you're satisfied that you have +4 dBu coming out of your interface, patch it into your various analog devices. Then measure the output of that device with a multimeter in the same way as before, tweaking the device's gain knob(s) and/or fader(s) until you see 1.23 V on the output. If the device has multiple gain stages, each should be set close to its nominal, 0 dB position. Any VU meters on the device calibrated to +4 dBu should be showing 0. Bypass the signal generator and run music through the signal path -- how does it sound? If it sounds distorted or otherwise crappy, the device is likely expecting -10 dBV signals (some can be switched between -10 dBV and +4 dBu, but if not, you'll have to lower the output of whatever's in front of it to about -0.3 V.) Or maybe music through the device sounds fine, but when you lower the input and raise the output it sounds even better!

Do the same for all your devices, experimenting with different input and output levels, and soon you'll have your equipment gain-staged properly, your confidence will be higher, and women will find you more attractive.

Edit: for mic inputs on preamps, there's no such thing as nominal levels -- it depends too much on the source and microphone. Shoot for roughly the same levels in your DAW's meters as line-level signals.
Just created an account to say thanks for this post (and probably should have before as I lurk too much), I know its old but it has realy helped me understand this whole thing a lot better (well, a bit more than I did), it's amazing how the maths involved all worked out perfectly, I worked out the differences between two equations and it seemed to give me the answer for another question I had so I didn't have to guess or use a special conversion calculator, amazing really.

I wonder, as lots is posted about maximum output, what of maximum input going in. would you do the same

for instance my maximum output on the interface is +15.78dbu, so I knew to test with -11.78dbfs, which gave me exactly 1.228v AC on the outs, went through the mixer, had to gain the mixer channels so it gave me 0dbu (+4) on vu the which was 1.228v AC on the outs

then it all goes back into the interface, now I found I had to pull up the input gains on the interface to -11.78dbfs & took a reading out a spare output routed directly from the inputs and it came up as 1.228v AC on each channel so it seems I have +4 all round

it struck me though as you calibrate according to your equipment max output - 4, what of the input stage

maximum input for my interface is a lot different from the max output, max input is 28.5dBu, surely the nominal input would then be around 24.8db, a lot lower than what I'm feeding it to maintain the nominal output, maybe it correlates anyway.

This where I've baffled myself, I suppose I wouldn't always be feeding it as loud with a test tone, maybe I'm mixing up my dbs as I'm away from the system, maybe I need to experiment a bit more, maybe test with some different levels of test tone/noise etc

Last edited by footokay; 20th June 2015 at 11:30 AM.. Reason: Missing words/grammar
Old 20th June 2015
  #12
Lives for gear
 
🎧 15 years
It's great that you can do the math and come up with real and meaningful numbers, but it isn't really all that necessary to do that in normal, day-to-day engineering.
I myself am way too lazy to apply math and then because I am so far removed from using it I wouldn't trust my results.
However, I have worked professionally for over forty years and I have rarely had to do calculations to come up with the optimal gain staging.
The key is experience and listening along the way.

I work mixing large-scale corporate events and I build rather complicated sound systems from individual components on a constant basis.
I my favor, I am provided with the very latest equipment and I do see mostly the same hardware, but I don't have to really use math to engineer a rig.
Plus, I don't have the time to get that detailed and I know the range of acceptability that I can work within.
The only time "math" ever gets close to being used is when I am stringing together arrays of loose speaker cabinets (usually JBL VRX.)
Still, I am not doing the actual Ohms Law calculation.
For example, If I am running two 8 ohm boxes I know that the load is 4 ohm load with two boxes and if I use three I know that the load is down around 2.6 ohms.
I already know which amps can handle 2.6 ohms, so off we go!
Pretty dang simple, stuff.

Truthfully, math can be applied to explain a situation and build a theoretical signal path.
I just find that common sense and a feel for the gear should allow you to work within an acceptable range.

Don't over think it!
Old 20th June 2015 | Show parent
  #13
Lives for gear
 
🎧 5 years
Quote:
Originally Posted by dbbubba ➑️
It's great that you can do the math and come up with real and meaningful numbers, but it isn't really all that necessary to do that in normal, day-to-day engineering.
Actually, in the hybrid world when you track ITB and Mix OTB it is often necessary to know the math. It certainly doesn't hurt under any configuration.
Old 20th June 2015 | Show parent
  #14
Lives for gear
 
🎧 15 years
Quote:
Originally Posted by chainrule ➑️
Actually, in the hybrid world when you track ITB and Mix OTB it is often necessary to know the math. It certainly doesn't hurt under any configuration.
Yeah... I've been thru that...
I have been using A/D and D/A converters with all manners of consoles for many years (since '95.)
Getting everything to play together properly can be a big undertaking (I posted about on GS this years back.)
Still, I was able to get everything to work properly by using a decent tone generator and my brain.
I did have to look into the math of why MOTU AD/DAs which were supposed to be a +4 balanced boxes couldn't handle the output of a properly set up JH-24.
However, the math didn't solve the issue.
It only confirmed the reason why things were not doing what they were supposed to be doing.
The answer as to why there was a mis-match came from MOTU's design engineers who explained why the boxes clipped.
They provided the math, but seeing it didn't solve any problems.
The only solution, no matter what the numbers said, was to dial back the output of the JH-24 a few dbs.

Maybe math could help someone who doesn't have a good feel for gain structuring, but I was able to set up the gain structure with both MOTU and Avid AD/DAs on a JH-538C without the console's meters functioning.
Once I did get the F-ing PLASMA METERS working and calibrated I was surprised to see that I was within three dbs of my targeted gain.

I guess it depends on how you want to approach things.
Old 20th June 2015
  #15
Gear Guru
 
Brent Hahn's Avatar
 
1 Review written
🎧 15 years
It's kind of a given that healthy levels coming off a +4 tape machine are going to be a bit much for an AD converter, even if the converter nominally operates at +4.
Old 20th June 2015 | Show parent
  #16
Here for the gear
 
🎧 5 years
Quote:
Originally Posted by dbbubba ➑️
It's great that you can do the math and come up with real and meaningful numbers, but it isn't really all that necessary to do that in normal, day-to-day engineering.
I myself am way too lazy to apply math and then because I am so far removed from using it I wouldn't trust my results.
However, I have worked professionally for over forty years and I have rarely had to do calculations to come up with the optimal gain staging.
The key is experience and listening along the way.

I work mixing large-scale corporate events and I build rather complicated sound systems from individual components on a constant basis.
I my favor, I am provided with the very latest equipment and I do see mostly the same hardware, but I don't have to really use math to engineer a rig.
Plus, I don't have the time to get that detailed and I know the range of acceptability that I can work within.
The only time "math" ever gets close to being used is when I am stringing together arrays of loose speaker cabinets (usually JBL VRX.)
Still, I am not doing the actual Ohms Law calculation.
For example, If I am running two 8 ohm boxes I know that the load is 4 ohm load with two boxes and if I use three I know that the load is down around 2.6 ohms.
I already know which amps can handle 2.6 ohms, so off we go!
Pretty dang simple, stuff.

Truthfully, math can be applied to explain a situation and build a theoretical signal path.
I just find that common sense and a feel for the gear should allow you to work within an acceptable range.

Don't over think it!
Yeah that's fair, I've always been an advocate for just getting on with it - I know sweet fa about most of this really for as far as I have managed to wing it. I'm such a total noob past seeing that everything (in my set up) has its own idea where 0 is and what 0 means that it's annoying.

I've always made music and thought all this stuff best left for the brainboxes of the world to ponder and didn't care as long as it sounded okay, in retrospect some things didn't sound as good as I thought at the time but there's a fair few subjects in that one.

I found myself fighting a few mixes on my last set up and thought of giving myself a bit more headroom now we don't have to grab every last bit and record near 0 in the digital domain any more.

so to put it simply - I turned it down

Not sure if it was confirmation bias at work, but once I did that without any reference, things started to sound better in listening comparisons at relative volumes

I've just set things up again and wanted to look a bit more what is actually happening and realised I knew a lot less than I thought was going on, between itb and out the box and a few items in the chain I have, seems like I had been smashing the hell out of things waaaaay beyond their operating level, then saw a 200 page thread on here which seemed like it made sense, people were quoting this magical -18db number so I looked into where this was coming from

I tried that and it was okay, then it made me think, what is the actual best operating level for my equipment, you know - you can read stuff online but if you don't test and check things for yourself you can be led astray, so many things that are total nonsense still get thrown about on various fora.

I'm terrible at math, I can't even add 15 and 43 without having to think for about 3 minutes, I do find it fascinating, beyond the world of audio. In fact I'm probably obsessed with numbers or the logical way they interact in all sorts of weird and wonderful ways.

of course when mixing a record I'm not even watching any specific numbers

Last edited by footokay; 20th June 2015 at 05:07 PM.. Reason: their not there
Old 20th June 2015 | Show parent
  #17
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bogosort's Avatar
 
🎧 10 years
Quote:
Originally Posted by footokay ➑️
maximum input for my interface is a lot different from the max output, max input is 28.5dBu, surely the nominal input would then be around 24.8db, a lot lower than what I'm feeding it to maintain the nominal output, maybe it correlates anyway.
Hi, congrats on your first post. I think I understand your question: if the max input on your interface is different than the max output, which should you use to calibrate your DAW's meters? Why should the output have preferential status over the input? This is a good question!

To answer this, let's reflect on why we care in the first place. The nominal line level in pro audio -- whether input or output -- is +4 dBu. This is the voltage level that manufacturers have agreed to optimize their input and output stages for; a signal at +4 dBu will be in the sweet spot in terms of headroom and signal-to-noise ratio. In the all-analog days, this was handled easily by calibrating the meters such that 0 VU = +4 dBu. Both the gear and the meters were dealing with the same thing, voltage levels. Things are a bit more complicated in the DAW world because DAWs don't deal with voltages directly, they deal with bits, and typically the DAW has no idea what interface you're using and what voltages are represented by those bits. It's the converter's job to translate bits to voltages (and voltages to bits), so we -- the ones who are using the DAW -- need some way to "calibrate" the DAW's meters to the converter's voltages. Because a full-scale output on the DAW (0 dBFS) will correspond to a max voltage from the DAC, once we know the DAC's maximum output we can translate bits-to-volts and figure out what level of dBFS matches +4 dBu.

But what if the maximum voltage levels are different on the interface's inputs and outputs? Why shouldn't you use the max input level to calibrate your dBFS level? Well, think about it this way: your interface is in complete control of the voltage level coming out of the output. If the max output is +16 dBu, and the DAW sends 0 dBFS to the interface, then +16 dBu will come out of the output. The gear that is connected to that output has no say in what voltage is coming to its input; it will see +16 dBu, regardless of what its max input voltage may be. Let's say the next piece of gear is a compressor with max input voltage +24 dBu. Does this information help us know what voltage the interface's output is sending? Nope, it can't. The output is responsible for the voltage level; the input can only receive it.

Hopefully it is now clear why we use the interface's output and not the input to calibrate the meters: the maximum input voltage has no bearing on what voltage is actually coming into the interface. The fact that your interface has more headroom above nominal at its inputs than its outputs doesn't change the bits-to-volts calibration in your DAW.

Quote:
This where I've baffled myself, I suppose I wouldn't always be feeding it as loud with a test tone, maybe I'm mixing up my dbs as I'm away from the system, maybe I need to experiment a bit more, maybe test with some different levels of test tone/noise etc
As many have said, the only thing that matters is how it sounds. I do believe that what you're doing is important, something that everyone should do at least once. But once you get your head around it all, once you have an intuitive feel for what the DAW meters should look like, you pretty much never have to think about it again (unless you change your interface). Remember that all this +4 dBu stuff is based on 1 kHz sine, and it is meant only for calibration, to set all your gear in the sweet spot. The numbers don't matter once you start tracking or mixing music; always go with what sounds good!
Old 20th June 2015
  #18
Here for the gear
 
🎧 5 years
Thank you, thank you so much.

This will be only a very brief reply for now as I am currently out. I will thank you now for taking the time to explain in such a detailed yet simple enough for me to get my head around way

It's why I picked the original post you made to help me understand, and base some tests off. It was the best post on the subject I could find.

I think my worry was that I could be 'smashing' things into the input if I kept consistency, this definitely seemed much more intuitive when I didn't use a DAW to record back into.

I've read and re-read your reply [to me] and it completely makes sense, you have clarified a great part of the question was indeed "why am I doing this and why do I care" and with the extra information you have given me, it seems more obvious now the more thought I give to it, I must thank you for clearing this up completely and so succinctly for me.

It is actually one of those times, I've just set up an interface after not having a set up for quite some time, I think it pays to test things yourself and know why you are doing them rather than only to take things that you've heard or read as gospel

I do understand though, it is only a calibration thing as [hopefully] music is a lot more complex and dynamic than a 1khz sine

It does sound so much better than when I was pushing things near digital 0 before, and now I know why!
πŸ“ Reply

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