Gearslutz

Gearslutz (https://www.gearslutz.com/board/)
-   Newbie Audio Engineering + Production Question Zone (https://www.gearslutz.com/board/newbie-audio-engineering-production-question-zone/)
-   -   +4db, -10db...what does all this mean exactly? (https://www.gearslutz.com/board/newbie-audio-engineering-production-question-zone/566766-4db-10db-what-does-all-mean-exactly.html)

cnlgs 4th January 2011 12:51 AM

+4db, -10db...what does all this mean exactly?
 
Hi ,and let me state first of all that i have no clue as to where the appropriate place for the following question on gearslutz.
So do feel free to move it elsewhere .


The question is simple I hope .
In recording one is often confronted with +4db and -10db when matching equipment; say a preamp to a recording device (in my case an apogee duet with a preamp that feeds it).
When I set the duet to +4 the levels are quite low, when I set it to -10 they are as I'd expect them to be.

Plus...what confuses me is that the levels on the duet look alright on both +4 and -10, but the recording levels in logic 9 are not looking the same and always appear lower than indicated on the duet. As if something turns them down on the way...

Would anyone here feel able and willing to explain this to me?
..and what does all this mean in terms driving recording devices etc that are linked with varying lengths of cables( sometimes I have to link to desks and tape machines etc that are quite a few meters away.

Thanks in advance and sorry if I posted in the wrong section.abduction

Fletcher 4th January 2011 01:10 AM

The difference between +4dBu and -10dBV [commonly shortended to "+4" and "-10"] is about 11.79dB [the difference is based on a logarithmic scale so its not a straight "14 db" as you might think]... what complicates it further is that you're dealing with two different scales [dBu being "dB - un weighted" and dbV - dbVolts"] both with a reference to 0db = .775volts... dBu can be used regardless of impedance, but is derived from a 600 Ω load dissipating 0 dBm (1 mW).

In your case - when you set the input level to "-10" you're increasing the input gain [by 11.79 db]... which originally done to reduce the noise level in "semi pro" equipment [hotter signal in, less noise... also less headroom and a whole bunch of other issues but I have a feeling I've already gone a little too far with the explanation].

Hope this is of some assistance.

Peace.

Ward Pike 4th January 2011 01:42 AM

Well said, or explained, Fletch. Also note you may find some pieces have a set switch for choosing between +4dbu and 0dbu. And many other variations of the like.

mister sunshine 4th January 2011 03:27 AM

big V or little v?

Aisle 6 4th January 2011 04:56 AM

Quote:

Originally Posted by cnlgs (Post 6177528)
When I set the duet to +4 the levels are quite low, when I set it to -10 they are as I'd expect them to be.

Plus...what confuses me is that the levels on the duet look alright on both +4 and -10, but the recording levels in logic 9 are not looking the same and always appear lower than indicated on the duet. As if something turns them down on the way...

Would anyone here feel able and willing to explain this to me?
..and what does all this mean in terms driving recording devices etc that are

You may be seeing what looks to be incorrect levels, but in actual fact they are accurate. This is because digital scale and analog scale are different. There is about 18dB difference as digital reaches full scale peak (clip) at 0dB whereas analog will peak at anything from about +12 to +28dB or even more depending on the headroom of the design. This can make matching signal levels seem difficult.

Ward Pike 4th January 2011 05:53 AM

Excellent point, Aisle 6. Some of us learned a long time ago that you can't even get the full headroom out of many good pre's when going into PTHD because it just can't cope with that kind of level!

youngmain 4th January 2011 08:52 AM

I gotta give thanks for the info. Awesome.

Unexplainedbacon 4th January 2011 08:59 AM

This is one of those questions I've been afraid to ask. Great response, thank you!

cnlgs 4th January 2011 11:08 AM

Thank you very much for all the replies!
All this leads to a couple more questions...
How exactly do you define "headrom"?
and what does "PTHD" stand for.

So all is quieter at +4 because the input expects a higher level and adjusts to that?( A bit like on active and passive inputs on guitar and bass amps?

And is it a matter of the pre not having enough gain?

Thanks again!!abduction

camus 4th January 2011 11:32 AM

Quote:

Originally Posted by cnlgs (Post 6179145)
How exactly do you define "headrom"?

Headroom in an analog device is the difference between the nominal operating level (0VU) and the maximum output level (clipping/distortion).

Digital has no headroom. Your calibration level (0VU=-20dBFS, -18dBFS etc) determines the amount of headroom you give yourself.

Quote:

So all is quieter at +4 because the input expects a higher level and adjusts to that?( A bit like on active and passive inputs on guitar and bass amps?
Not really. When you set your Duet to either +4dBu or -10dBV operation, all you are telling it is how much analog voltage is needed to measure "0VU" on the device. I'm not sure whether you can actually calibrate the inputs on the Duet, but this figure will probably be something from around -20 to -18dBFS.

This is why your recording levels appear "higher" digitally when you switch down to -10dBV. The analog level you are feeding it is the same, it is just that you have switched to a lower scale of measurement, so to speak, on your digital interface. I sometimes do this on my MH 2882 when using very low output dynamic microphones to get a "decent" level, instead of working the analog preamp at the extreme end of its gain range which tends to increase the S/N ratio significantly in the device.

mister sunshine 5th January 2011 02:43 AM

Quote:

Originally Posted by Fletcher (Post 6177580)
The difference between +4dBu and -10dBV [commonly shortended to "+4" and "-10"] is about 11.79dB [the difference is based on a logarithmic scale so its not a straight "14 db" as you might think]... what complicates it further is that you're dealing with two different scales [dBu being "dB - un weighted" and dbV - dbVolts"] both with a reference to 0db = .775volts... dBu can be used regardless of impedance, but is derived from a 600 Ω load dissipating 0 dBm (1 mW).

In your case - when you set the input level to "-10" you're increasing the input gain [by 11.79 db]... which originally done to reduce the noise level in "semi pro" equipment [hotter signal in, less noise... also less headroom and a whole bunch of other issues but I have a feeling I've already gone a little too far with the explanation].

Hope this is of some assistance.

Peace.

Greetings,

0dBu and 0dBv both = 0.775 volts.

Semi pro gear is specified at -10dBV with a large "V".

0dBV = 1 volt regardless of impedance load.

dBu and dBv are considered interchangeable but, as mentioned above, dBv suggests that the voltage is measured across a 600ohm load. There is very little 600 ohm gear made today so the use of dBv has been deprecated and replaced by the dBu unit which is measured regardless of impedance.

The reason one can observe that there is only 11.79dB difference between +4dBu and -10dBV is that they are referenced to different values. Recall that 0dBu = 0.775 volts and 0dBV = 1.0 volts.

So the statement that

"the difference is based on a logarithmic scale so its not a straight "14 db" as you might think"

is completely erroneous. The use of decibel units takes care of all the logarithmic relationships and the apparent 14dB difference between the -10dBV and +4dBu is actually 11.79dB because the units simply reference different absolute values.

for example;

+4dBu = 1.23 volts and -10dBV = 0.316 volts

0.316 volts = -7.79dBu

4dBu - (-7.79dBu) = 11.79dB difference

or for example;

+4dBu = 1.23 volts = 1.78dBv

1.78dBV - (-10dBV) = 11.78dB difference

When either value is reconciled to the others reference value and the actual difference in voltages are compared there is a 11.79dB difference.

It's actually quite simple, but some people like to make it seem complicated.


The history of -10dBV is simply that old hi-fi gear was made to have lower output than professional gear as a cost saving measure.

When a pro item has a -10dBV input option the intention is to use the gain in the pro item rather than forcing the user to over drive their -10dBV gear into a input that expects a +4dBu signals. The idea is that you use the semi pro gear in it's sweet spot and the pro gear has enough gain to handle the rest.

An obvious question is to ask whether the *pro* gear is optimized for +4dBu or -10dBV. If the former, it will have adequate head room above and beyond +4dBu. Perhaps +26dBu max or 22dB headroom. If the *pro* gear is optimized for -10dBV then the +4dBu input may simply be padded to bring down the pro grade levels to the semi pro region. This would be done for cost cutting reasons and the headroom above +4dBu will generally be well below 22dB in those devices.

The only reason to use a -10dBV input is if your gear only works at -10dBV standard levels. In all cases connecting a -10dBv output to the input of +4dBU gear will increase the noise floor... if you do so and need to gain up to +4dBu nominal levels it is often cleaner to do it in the pro side of the connection.

If you connect a +4dBu output to a -10dBv input then you are sending a hot signal over the line and this will minimize the noise floor but it will also be hot and may overload the input. If you pad it down you may reduce the noise floor a bit but the -10dBV input will have to rebuild the gain if it goes further to another +4dBu device and the noise will likely return at the next stage.



best regards,
mike

youngmain 5th January 2011 05:06 AM

Superb information.

E.rOk.stA 5th January 2011 05:35 AM

I literally was just contemplating this today. I was tryin' to see if I would get a better signal runnin my 1073 DPA into 003 at -10 or +4? I just wanted the best gain stage.

I'm still not clear which setting I should have on the -10/+4 switch of the line ins of my 003 to have the lowest noise floor.

myles 5th January 2011 09:27 AM

Quote:

Originally Posted by E.rOk.stA (Post 6182526)
I literally was just contemplating this today. I was tryin' to see if I would get a better signal runnin my 1073 DPA into 003 at -10 or +4? I just wanted the best gain stage.

I'm still not clear which setting I should have on the -10/+4 switch of the line ins of my 003 to have the lowest noise floor.

"Better"?

Look, the whole thing is based on machines being similar. +4 is a professional, high-level standard. Used to be, all the stuff you'd find in a studio was +4, it all played nice together.

-10 came into the studio in the 80's with the first home recording stuff. Manufacturers realized that home recorders didn't want to pay pro prices, and that 97.3% of the time, they wouldn't notice if all their equipment used RCA plugs because everything would operate at -10, with input sensitivities and output levels matching up. Noise was demoted in importance.

The problem now is that manufacturers started placing +4/-10 switches on things to help interface equipment that used different operating levels, and everyone's confused.

Now - is the 003 rated at +4 or -10? Is the 1073 rated at +4 or -10?

You'd want to use +4 on the 003 unless the 1073 is rated at -10, which is doubtful.

+4 on output = more voltage, stronger output

-10 on output = lower voltage, lower output

+4 on input = less sensitive, but capable of handling much greater voltages, hence more headroom - it can take more level before distorting

-10 on input = more sensitive input, coresponding to the lower output of -10 equipment.

So, the danger in going from a -10 device to a +4 device is raised noise floor as the +4 machine makes up for the feeble output from the -10 machine.

The danger in going from a +4 machine into -10 is distortion on the input of the -10 machine because it can't handle the larger voltage swings from the +4 machine.

Now, if you don't understand the difference between voltage and current, and how something could be referenced to a certain voltage, please, you really should grab a basic electronics book and read it. You'll lose a couple of days of your life, but then you'll actually begin to understand what your equipment is doing, and everything you record the rest of your life will be better.

E.rOk.stA 5th January 2011 06:44 PM

Excellent! I'll do just that.
Quote:

Originally Posted by myles (Post 6183002)
"Better"?

Look, the whole thing is based on machines being similar. +4 is a professional, high-level standard. Used to be, all the stuff you'd find in a studio was +4, it all played nice together.

-10 came into the studio in the 80's with the first home recording stuff. Manufacturers realized that home recorders didn't want to pay pro prices, and that 97.3% of the time, they wouldn't notice if all their equipment used RCA plugs because everything would operate at -10, with input sensitivities and output levels matching up. Noise was demoted in importance.

The problem now is that manufacturers started placing +4/-10 switches on things to help interface equipment that used different operating levels, and everyone's confused.

Now - is the 003 rated at +4 or -10? Is the 1073 rated at +4 or -10?

You'd want to use +4 on the 003 unless the 1073 is rated at -10, which is doubtful.

+4 on output = more voltage, stronger output

-10 on output = lower voltage, lower output

+4 on input = less sensitive, but capable of handling much greater voltages, hence more headroom - it can take more level before distorting

-10 on input = more sensitive input, coresponding to the lower output of -10 equipment.

So, the danger in going from a -10 device to a +4 device is raised noise floor as the +4 machine makes up for the feeble output from the -10 machine.

The danger in going from a +4 machine into -10 is distortion on the input of the -10 machine because it can't handle the larger voltage swings from the +4 machine.

Now, if you don't understand the difference between voltage and current, and how something could be referenced to a certain voltage, please, you really should grab a basic electronics book and read it. You'll lose a couple of days of your life, but then you'll actually begin to understand what your equipment is doing, and everything you record the rest of your life will be better.


nosebleedaudio 5th January 2011 07:24 PM

It IS confusing...
Gain staging can be VERY confusing...
Fact is -10 gear has NOTHING to do with noise or headroom...
-10 gear can have the same maximum output level as some +4 gear...
Noise mostly comes from some gear when the gain is cranked TOO much..
Some gear has less noise than others, all other varibles the same..Design, circuit ect...

But will add that most mic pres are better at higher gain (Less noise) than some gear's "Make up gain"...all depends..

Also 0dBV is 1 Volt RMS.
0dBm,dBu is .775V RMS...

It is best to keep ALL gear at same level and balanced...IMHO..less problems..

Flying_Dutchman 6th January 2011 12:45 AM

haven´t seen new -10dbu gear since more than 10-15 years
"chinese" reference level, electronic circuits with lower voltage guidelines = cheaper parts = "home recording"
"semi pro" tape machines i got use it and sansamp psa1 is switchable
but i think it´s history
just keep your gear talking face to face and not like master and servant ^^

Etch-A-Sketch 6th January 2011 02:01 AM

Here's a dB/Volt calculator with some charts, explanations and formulas below the calculator...this might help shed some light on the subject as well...

dB dBu dBFS dBV to volts conversion - calculator volt volts to dBu and dBV dB mW - convert dB volt relatioship relation convertor converter calculation online attenuation loss gain ratio reference audio engineering sound recording dBFS dBVU 0 dB audi

mister sunshine 6th January 2011 02:17 AM

All you need to know is

If you plug a +4dBu output into a -10dBV input the signal is coming in 11.79dB hotter than the gear was designed for... turn something down.

If you plug a -10dBV output into a +4dBu input the signal is coming in 11.79dB quieter than the gear was designed for... turn something up.

it is simple.

best regards,
mike

E.rOk.stA 6th January 2011 02:39 AM

Quote:

Originally Posted by mike_mccue (Post 6185741)
All you need to know is

If you plug a +4dBu output into a -10dBV input the signals coming in 11.79dB hotter than the gear was designed for... turn something down.

If you plug a -10dBV output into a +4dBu input the signals coming in 11.79dB quieter than the gear was designed for... turn something up.

it is simple.

best regards,
mike

Nice.

pongmaster 6th January 2011 08:21 PM

.
 
since nobody mentioned it.
lots of -10dbv gear is also unbalanced.

for that task studio and broadcast etc. always used
balancing amps, like from studer or tascam etc.

like this one for example:
eBay Österreich: STUDER STEREO BALANCING UNIT (Artikel 250729892809 endet 28.11.10 21:00:07 MEZ)

TC2 9th January 2011 02:26 AM

Let me make sure that I understand correctly...sorry, I'm a newbie.

I'm trying to get an old recording off my 80's era 4-track into my computer thru my Firestudio. The 4-track has RCA outs at -10dB. I'm OK running them to the line inputs on my Firestudio (+4dB), then, but the gain to get the signal up to par is going to mean noise?

Is there any way to avoid the noise?

cnlgs 9th January 2011 02:58 AM

Thanks all!

So the +4 and -10 thing has nothing to do with how much gain a pre can give?
(say, a pre that has a 0-65db range can be rated at +4 whilst another with the same gain range can be rated at -10?)?

Which part of the pre amps inerts is responsible for this rating?

Thanks again!!abduction

pqlia 25th February 2013 05:33 PM

I’ve read through this thread and I’m not a newbie to recording so really ought to know the answer to this… but other than changes in absolute level can a mismatch from preamp into soundcard affect the sound quality in any subtle way --- is it JUST simply a level thing ?

myles 25th February 2013 05:52 PM

Quote:

Originally Posted by mike_mccue (Post 6185741)
All you need to know is

If you plug a +4dBu output into a -10dBV input the signal is coming in 11.79dB hotter than the gear was designed for... turn something down.

If you plug a -10dBV output into a +4dBu input the signal is coming in 11.79dB quieter than the gear was designed for... turn something up.

it is simple.

best regards,
mike

Quote:

Originally Posted by pqlia (Post 8783085)
I’ve read through this thread and I’m not a newbie to recording so really ought to know the answer to this… but other than changes in absolute level can a mismatch from preamp into soundcard affect the sound quality in any subtle way --- is it JUST simply a level thing ?

Yes, this will be on the final.*

*The only modifiers to Mike's clear, simple answer are:

Gear designed to operate at +4 is/was usually designed for professional operation, which is an old concept whereby people made money using recording equipment in places called "studios". As a result, this equipment often was well-designed, well-built and not made to a price point. As a result, it often had relatively low noise in normal operating conditions.

Gear designed to operate at -10 was usually consumer or "pro-sumer" gear, and often was designed for less critical operating conditions. As a result, it often had higher noise levels in normal operating conditions.

-10 equipment was, as the poster above noted, usually unbalanced, which could add to or exacerbate the existing noise, and could make interconnection with +4 gear somewhat hit-and-miss. There are a number of good references out there for how to do this (Rane had a good tech paper).

There are and were exceptions to these general rules. You're not going to hurt anything by looking at the interconnection guides, following their recommendations, and giving it a shot.

Then again, this whole thread could have been answered with a Google search.

pqlia 25th February 2013 06:27 PM

Been recording for a loooooong time.. but never been very technical … maybe that much is obvious by my posts … :lol:

It could be that I’m misunderstanding this mismatch … I completely understand the history of -10 db and + 4db … but I know that generally input/output mismatches can cause changes in frequency response as well as level changes in studio equipment … I was just wondering if the same applies with sound card -10 db/ + 4db mismatches....

Perhaps i'm just missing something ... :facepalm:

jaxman12 25th February 2013 06:46 PM

This thread needs to be stickied. One of the best threads I've seen. I am right in the middle of learning this and how it relates to what I am doing. Thanks for all the great post.

myles 25th February 2013 06:57 PM

Quote:

Originally Posted by pqlia (Post 8783250)
Been recording for a loooooong time.. but never been very technical … maybe that much is obvious by my posts … :lol:

It could be that I’m misunderstanding this mismatch … I completely understand the history of -10 db and + 4db … but I know that generally input/output mismatches can cause changes in frequency response as well as level changes in studio equipment … I was just wondering if the same applies with sound card -10 db/ + 4db mismatches....

Perhaps i'm just missing something ... :facepalm:

If equipment is working correctly, level mismatches will have no frequency response effect, unless it's gross input distortion.

If you're talking about impedance matching, then, yes, that can have effects on frequency response, but that's more important for something like a microphone, which operates at a very low level.

+4 and -10 equipment can have different input and output impedances, but, in this case... I don't want to say it's not important, it's not the most important thing. If you were driving a mile of cable, then there might be cause for concern, but I doubt that's the case.

If anyone who's reading this is in any form of organized education, take a physics course while you have the opportunity. Or read any of the standard books on the subject - Sound System Engineering, you can get the US Navy electronics texts online, there's lots of resources out there.

Removing any possible temptation to engage in magical thinking, much less removing a source of confusion, really makes life a lot easier.


EDIT: I just realized I said pretty much the same thing earlier in the thread, but it's worth saying again. Everyone can learn this stuff. And if you can, you should.

pqlia 25th February 2013 07:00 PM

'' If equipment is working correctly, level mismatches will have no frequency response effect, unless it's gross input distortion.

If you're talking about impedance matching, then, yes, that can have effects on frequency response, but that's more important for something like a microphone, which operates at a very low level. ''

Good stuff ! many thanks myles !!

myles 25th February 2013 07:11 PM

Quote:

Originally Posted by TC2 (Post 6196629)
Let me make sure that I understand correctly...sorry, I'm a newbie.

I'm trying to get an old recording off my 80's era 4-track into my computer thru my Firestudio. The 4-track has RCA outs at -10dB. I'm OK running them to the line inputs on my Firestudio (+4dB), then, but the gain to get the signal up to par is going to mean noise?

Is there any way to avoid the noise?

Nope. But you might be surprised at how little noise there is, if you follow the correct procedure in making or buying your cables. (Big plug here for learning how to solder and make your own cables - it's not hard, saves money and you can do all the weird interconnects at 2 am when no stores are open and you need them right away).

Quote:

Originally Posted by cnlgs (Post 6196736)
Thanks all!

So the +4 and -10 thing has nothing to do with how much gain a pre can give?
(say, a pre that has a 0-65db range can be rated at +4 whilst another with the same gain range can be rated at -10?)?

Which part of the pre amps inerts is responsible for this rating?

Thanks again!!abduction

You're confusing internal gain with output level. Both of your pre's can deliver 65dB gain, but the +4 pre will consistently be 14dB hotter at the output for the same gain as the -10 pre - it's just the way they're designed.

The output amp of the pre is responsible for the rating. If we were talking about line level gear, a +4 piece of equipment could accept higher levels coming in, as well as deliver higher levels going out.