Basic Gain Staging

C

ChrisPFuchs

New member
Hi, I have a few questions regarding basic gain staging of my setup.

First, I have my microphone plugged into a Mackie ProFX8 mixer. After the mixer, it is getting sent out the main outputs into the corresponding line inputs on a LineSix Ux1, which is acting as my recording interface. It is set to record at 16bit/48kHz. This is plugged into my computer via USB, and I'm recording using ProTools 11.

There is a light on my mixer that lights up to help notify you to when you have a good level set for the gain nob. There is a second light that lights up to signify clipping. Generally, I set gain and keep the fader at unity. I also am keeping the main faders at unity. The level of which my preamp is set should then be getting sent out of the main outs at the same level.

I notice the light that signifies I have a good level set flashes exactly at 0dB on my Main Meters on the mixer. These meters are labled 0dB = 0dBu. 0 dB is in the middle of these meters with OL being more than 15dB above that. If the signal is steady around 0dB on the mixer, with the amount of headroom, usually there is plenty enough headroom for the transients. At this point, everything seems normal and how it should be.

Now, what I don't understand is as it gets recorded into Protools, a signal playing (I tested this with a 500 Hz sine wave) at exactly 0dB on my mixer is being recorded at -5dB in Protools. I understand that Protools has a different measurement for their meters. Since it's digital, Protools has it's meters in dBFS, so 0 is the point of clipping. The dynamic range between -5 dBFS and 0dBFS is tiny compared to the 0dB and +15dB of headroom on my mixer.

-Why is it that Protools will clip way before my mixer would ever overload?
-If I recorded at a 24bit rate, would the headroom in Protools raise so that the 0dB signal on my mixer equals to less than the -5dBFS with me recording in 16bit?

I've been taught to record into Protools at roughly -18 dB. This gives plenty of headroom. If I were to set the level of my Sinewave to record at -18dB in Protools, I dramatically have to turn down the gain or the fader in order to lower it to that level. The equivalent on the mixer shows that at around -20dB is equal to -18dBFS on the Protools meters.

-When it does clip in Protools when recording (but not overloading on mixer), it totally flattens the waveform as expected, but it doesn't actually sound distorted, more like very compressed? Why is this? Why doesn't it have a nasty distorted sound? Does anyone know what's causing this, or at what point the signal is getting clipped? Is it at the converters? I don't have a limiter or anything like that in my signal chain.
-To record at an acceptable level in Protools, I need to lower the levels on my mixer a lot. Should I lower the gain control on my mixer or the fader? I see two possible ways of thinking. One is that I could set the gain to hit 0dB on the mixer like normal, but then lower the fader a lot until it reads around -18dB in Protools. The other way of thinking is to lower the gain, because as I boost the gain, it introduces extra noise, and since I don't need the volume, might as well keep the noise out and the volume lower.

I just don't want to be missing something important, or have my gain set too low in order to record at a proper level in Protools.

If anyone can clear up some confusion, I'd really appreciate it, and thanks for taking the time to read my post.

-Chris F
 
Oh, I should point out that when It does clip in Protools, it isn't actually activating the red rectangle (that signifies clipping). It simply just stops at 0dBFS and clips off the waveform in a non-distortion sounding way. I don't understand this. You'd think it would simply have the normal digital distortion sound. Which makes me think, if it's not clipping anywhere in the mixer, and it's not clipping in Protools, it has to be during the a/d conversion, right? Why would this be?
 
Sounds to me like a design issue in the Mackie, like the mixer puts out dBu and the converters expect dBV. Do you have to bring the faders down by about 12dB to make the levels right in PT?
 
-Why is it that Protools will clip way before my mixer would ever overload?
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There's nothing to say the two systems have to align.
Converters can and do use any number of input sensitivities. RME has three different scales/alignments to choose from. Some have trim pots.
In a simple mic>clean preamp>converter the rule of thumb is set your first stage- the pre amp, for the opt gain, or some compromise of preamp gain and record level. In you cases you can do that and use the master to trim further for your record level-- Typically average around -18 or so dBFS, peaks well below 0dBFS.
-If I recorded at a 24bit rate, would the headroom in Protools raise so that the 0dB signal on my mixer equals to less than the -5dBFS with me recording in 16bit?
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No, it lowers the converter's noise floor. The record level target is the same, dynamic range is added in the bottom level. 24bit makes lower record levels very forgiving.
 
Hi Chris,
the fly in this particular ointment is the UX1 IMHO.

The mixer is working properly and outputting a signal around +4dBu (abt a volt rms) when the "0" LED blinks. But the X1 probably has "domestic" sensitivity on the line inputs where I would guess +10dBV (3V) would cause full, 0dBFS modulation.

I have a similar situation with my A&H mixer. Of I wanted to use the (excellent!) on board meters to their full extent I would slam the 2496 card it drives to 0dBFS.

The solution in both cases is to introduce an attenuator twixt mixer and AI or ignore the mixer's meters and just go by those in the DAW, most often Samplitude in my case.

The simplest way to do the formers is a 10k log pot in a tin, fairly close to the AI end and use that to "calibrate" the system.

As for the lack of distortion on a "flattened" Pro tools? I don't have it but I would guess it has some form of "soft clip" facility?

Dave.
 
The easiest and most foolproof way to go would be to ignore the metering on the Desk, and use the digital metering in your DAW, since you are making a digital recording.

My first instinct would be to leave the faders on the desk at 0db/unity and then use the preamp to set the level - i would usually suggest that the metering on the mixer is irrelevant (aside from showing analogue clipping and signal overs within the unit) if you are using the system purely for digital recording.

Providing your faders are not themselves adding gain (keeping them below 0dB should, but more information might be available in the manual), reducing the preamp gain will probably give you less noise and distortion, though with most modern mixers this isn't a concern unless you are maxing out the preamp.

Out of interest, if your faders are all at 0dB, how much gain are you adding with the preamp?
 
One thing to look at..,

I see from the manual for your mixer that, although your mixer sends the main L/R channels to the USB output, it pulls this feed off BEFORE the main faders. Therefore, you gain staging has to be good at the channel level and not rely on any gain changes in the master section to adjust the USB feed.
 
Bobbsy said:
One thing to look at..,

I see from the manual for your mixer that, although your mixer sends the main L/R channels to the USB output, it pulls this feed off BEFORE the main faders. Therefore, you gain staging has to be good at the channel level and not rely on any gain changes in the master section to adjust the USB feed.
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He didn't say he had the USB version of the mixer - he's using the audio output to the Line 6.

One thing no one has mentioned - he's recording at -5dB - he's tracking too loudly, no? SHould be down in the -18 to -12 range.
 
Ah, sorry. Missed the bit about the UX1.

Yes, you're tracking too hot. If the UX1 had a level control on the line inputs I'd suggest putting some kind of tone through the mixer, adjusting level there to output 0dBu then set levels on the UX1 so that level is equivalent to -18dB(FS) on Protools. From then on, track with things averaging 0dBu on the mixer and peaks going to +6 or so...again on the mixer.

From the photo I found though, I can't see a line input level control on the UX1. Perhaps this is in software somewhere and, if so, you could still use the above method. Failing that, you'll just have to track lower and ignore the mixer meters (or at least get least to an arbitrary level you determine to keep things in the -18 to -12 dB(FS) range on your computer.
 
"The easiest and most foolproof way to go would be to ignore the metering on the Desk, and use the digital metering in your DAW, since you are making a digital recording."

Agreed and that is how son and I resolved the z10/2496 issue. Mind you, not before dad built a precision attenuator circuit using 22turn pots and installing it at the computer end of the chain but Son did not like the lower level having gotten used to hitting the card hard!

Kids, yer can't tell 'em nothing! (he was 39 at the time)

Dave.
 
Ignore the metering on the mixer.

Your interface expects a -10 dbv signal as line level, the mixer puts out a different standard as line level, which is higher. (It doesn't put out +4dbu, it puts out 0dbu for some stupid reason)

You should record at 24 bit. It keeps the noise floor far enough down that it will never be an issue and let's any processing errors stay well below any level that can be heard.
 
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Farview said:
Ignore the metering on the mixer.

Your interface expects a -10 dbv signal as line level, the mixer puts out a different standard as line level, which is higher. (It doesn't put out +4dbu, it puts out 0dbu for some stupid reason)

You should record at 24 bit. It keeps the noise floor far enough down that it will never be an issue and let's any processing errors stay well below any level that can be heard.
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Nice spotted that the Line6 is a -10dBv device...and brickbats to Line6 for producing it that way. What do they assume people will be plugging in? CD players or something?
 
Bobbsy said:
Nice spotted that the Line6 is a -10dBv device...and brickbats to Line6 for producing it that way. What do they assume people will be plugging in? CD players or something?
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Ha! I had a bit of a chug round for a specc' for the Line 6 but could find nothing.

It is a bit of a disease, giving all sorts of devices too much gain. Active monitors suffer this and are as a consequence noisier than they need be.

Line inputs and especially Instr inputs are often way too hot on AIs and so we see many tales of guitars producing not nice overload.

I can only conclude that the marketing/adpuff children put their oar in and want even the wimpiest plywood Strat to deliver well "into the red". The result is anyone with an even moderately hot pickup cannot avoid clipping (well, they CAN but gitists just don't like turning down their guitars!).

And even a CD player can produce 2V rms, +8.2dBu.

High sensitivity (if noise is low) has a place for microphone pre amps because although the cheaper AIs will not have the headroom an XLR attenuator is both cheap and readily available. Not so is a high Z input attenuator (tho' they are beer into water to make).

Dave.
 
Thanks for all the great replies!

It's a bit hard for me to wrap my head around the difference between dBu and dBV sometimes, but I guess what is happening is that Line6's Line Inputs expect -10dBV (Which is what, like -10 Volts?) as line input while the mixer is sending line level at a much higher voltage? What are the cons of the Inputs being set this way? It seems that they purposely did that to cater to the low end equipment they assumed people would be using with the UX1, or am I wrong in assuming that?

I guess ultimately the fix is to set the gain on my mixer to a much lower level and simply read the digital metering. I don't really feel satisfied with that though for some reason, like I still have questions. What would the need for powerful preamps be if you could simply have an a/d converter expect a lower voltage for it's input? If mic level is around .1 volts and the preamp is designed to boost the signal to line level, which I was taught is roughly 1V, what is the point of this, what exactly makes the realm of Line level for recording and mixing so special? Why not 10 volts or half a volt for that standard?

These probably seem like basic or stupid questions to more experienced people but you can see why simply lowering the level isn't satisfying for me. What are the possible consequences?

I'm probably over thinking this, and I really appreciate any clarification. Would I benefit from getting a decent interface to replace the Ux1? I have a partially broken PreSonus Audiobox which is worse than the Ux1 in my opinion. One more thing. Most home recording budget interfaces seem to have it's own preamps, line in and outs, headphone outputs, and usb or firewire connection to the computer, ect. Since I like using my mixer as an external preamp, is it practical to get a device that has no preamps of it's own but good converters and line outputs for my monitors? I've never really seen them for home studios, but that's what studios do right? They have a mixer and a patch bay and can send the signal to different preamps to get the sound they want, then each channel goes into a giant box that converts the signal to digital for the computer.

Thanks again for all the posts!
 
Pro & Non Pro Line Levels

"Professional Line Levels:The normal level of the audio signal in a professional studio is +4 dBu or about 1.23 volts (0 dBu=.775 volts). When the console output meters read "0" on a VU meter, the level of the signal is +4 dBu.

Non professional and Instrument Line Level:

The level of the audio signal in home stereo equipment, inexpensive "Semi-Pro" gear and in instruments (such as synthesizers, guitars, etc.) is -10 dBV or .316 volts (0dBV=1 volt). This lower "line level" (often called "instrument level") is about 12 dB lower than professional line level. "
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Again..
Set your mic pre gain first as per Mackie's guidelines - I.E. job one is to get the first stage optimized. This sets up the best you best sig to noise that will be passed on to everything else down stream.
Set the ch fader to zero, attenuate at the master fader to get the level back down if need be to good record levels on the DAW meter. (Lowering the master is also lowering whatever 'pre amp noise'- so no loss there.
Assuming the Mackie is '+4 nominal' standard (I didn't check) and the Line6 is '-10dBV' nominal (where did you get this spec, I couldn't find it?) , it might come out at '-12 on the mixer master fader.

Add.. The '-10dBV' doesn't mean 'lower quality. Like mentioned, RME for example give you the choices in sensitives, for its flexibility. One or the other is not less quality'.
 
ChrisPFuchs said:
It's a bit hard for me to wrap my head around the difference between dBu and dBV sometimes, but I guess what is happening is that Line6's Line Inputs expect -10dBV as line input while the mixer is sending line level at a much higher voltage?
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Yup, that's pretty much what's happening.

ChrisPFuchs said:
What are the cons of the Inputs being set this way?
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It just makes them easy to overload with equipment that runs at the higher line level.

ChrisPFuchs said:
I guess ultimately the fix is to set the gain on my mixer to a much lower level and simply read the digital metering. I don't really feel satisfied with that though for some reason, like I still have questions. What would the need for powerful preamps be if you could simply have an a/d converter expect a lower voltage for it's input? If mic level is around .1 volts and the preamp is designed to boost the signal to line level, which I was taught is roughly 1V, what is the point of this, what exactly makes the realm of Line level for recording and mixing so special? Why not 10 volts or half a volt for that standard?
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I suppose you could make the interface expect a lower signal level, but you wouldn't be able to get rid of the preamp because different mics have different sensitivities AND different sources are different volumes. The preamp is variable in order to get the signal from the mic, no matter how big or small, to the level that the next piece of equipment is expecting. If you are using a condenser mic 3 feet away from a jet engine on take off, or a ribbon mic across the room from a mouse farting, the preamp is there to get the level in the range that is needed.

ChrisPFuchs said:
These probably seem like basic or stupid questions to more experienced people but you can see why simply lowering the level isn't satisfying for me. What are the possible consequences?
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The only possible consequence is the chance that the self noise of the mixer will be about 10db more prominent. But that probably won't happen.

ChrisPFuchs said:
I'm probably over thinking this, and I really appreciate any clarification. Would I benefit from getting a decent interface to replace the Ux1?
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Probably not. The problem isn't really with the mixer or the interface. They are just set up for different standards. The Mackie isn't even set up for one of the two normal ones, it runs its line level in the middle of the two. This means that the meters on the Mackie will never correspond with the meters on anything else. It's 0dbVU is set to 0dbu, which is 4db less than the +4 standard, but not as low as the -10dbv standard. (the two different scales don't relate to each other, so it isn't obvious how much more voltage it puts out)


ChrisPFuchs said:
One more thing. Most home recording budget interfaces seem to have it's own preamps, line in and outs, headphone outputs, and usb or firewire connection to the computer, ect. Since I like using my mixer as an external preamp, is it practical to get a device that has no preamps of it's own but good converters and line outputs for my monitors? I've never really seen them for home studios, but that's what studios do right? They have a mixer and a patch bay and can send the signal to different preamps to get the sound they want, then each channel goes into a giant box that converts the signal to digital for the computer.
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Yes, this is what I did in my old studio. Look at MOTU for interfaces that do that.

However, the preamps in the Mackie are likely no better than the ones in a mid level interface (plus the goofy level issues), so unless you are in love with the workflow of the mixer, you don't really need it.
 
Farview said:
...
The Mackie isn't even set up for one of the two normal ones, it runs its line level in the middle of the two. This means that the meters on the Mackie will never correspond with the meters on anything else. It's 0dbVU is set to 0dbu, which is 4db less than the +4 standard, but not as low as the -10dbv standard. (the two different scales don't relate to each other, so it isn't obvious how much more voltage it puts out) ...
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I was thinking that might be the case with Mackies- I have a few but haven't thought about it lately.
 
Ahh ok, that helps, thanks!

And about the -10dBV nominal, I thought someone else had stated that earlier, but maybe I misunderstood.
 
Farview said:
Yes, this is what I did in my old studio. Look at MOTU for interfaces that do that.

However, the preamps in the Mackie are likely no better than the ones in a mid level interface (plus the goofy level issues), so unless you are in love with the workflow of the mixer, you don't really need it.
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That's a good point. I do prefer the work flow of the mixer, but I was thinking more along the lines of, if a device's only specific job is a/d and d/a conversions, then the converters would be better, rather than small interfaces which have to do a lot of different things. If I want more inputs, I'd have to also pay for the preamps too. It was just a thought though, I would probably prefer to have a higher quality interface. If only I wasn't a broke college student. There's other stuff I would like to spend money on first though involving audio.
 
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