Mixing multiple sources vs dB gain

[jorisds2]

Hi all,

I was wondering something and thought some of you might be able to explain this to me.

I’ve heard that 2 random audio sources combined should give a theoretical +3dB. I can see this on my 90’s analog dj mixer when I cue both tracks to 0dbu but when added it goes higher then 0 on the master.

How come with newer mixers like allen & heath, pioneer,… I can cue both tracks to 0 and also get 0 on the master? I don’t think it had anything to do with digital vs analog as the allen & heath ones that I’ve tried were all analog…

Thanks!

 

[gyraf]

explain what you mean by "cue", there may be some hint here?

 

[KrIVIUM2323]

Hi Jakob,
On dj mixer 'Cue' is headphone dedicated buss, sourced pfl most of the time, mostly used to make input gain and synchronise tracks bpm.

Joris, without a schematic it's difficult to say it can be done in many ways.

 

[Barry Hufker]

Two identical audio sources when combined would give you +3dB. And that is just +3 more than whatever the signal was reading previously. Two random audio sources mixed together could add (or cancel) to be anything.

In my radio days (when dinosaurs roamed), it was my job to make sure audio levels stayed in accepted parameters on the mixer ("the board"). I did that as necessary by adjusting "pots" (round knob potentiometers) or by adjusting faders (much later in life). With a digital mixer, anything is possible from compressors, limiters, auto gain, where levels are more maintained by the mixer to minimize user error or lack of attention. Analog consoles didn't usually have that. A DJ mixer is a special type of mixer where things are always happening with audio levels changing constantly. Compressors, limiters, etc. would be a handy way to help the DJ stay in control without having to be responsible for every error in level. As such the theoretical may not be the practical reality. Two identical signals could result in the level staying the same because the mixer pulled down the audio level.

 

[Newmarket]

Two identical audio sources when combined would give you +3dB. And that is just +3 more than whatever the signal was reading previously. Two random audio sources mixed together could add (or cancel) to be anything.

No. You do not need identical signal sources to see +3dB. In fact if they were identical AND in phase you would see +6dB.
Two non-correlated signals of equal level will sum to +3dB.

 

[KrIVIUM2323]

To add to possible confusion it depend of what we are talking about too: if we talk about a voltage ( what happen within an electrical circuit) it's +6db for two identical source ( we are on a 20log basis).

If we talk about radiated power level ( from an omnidirectional source= loudspeaker below baffle step = low and sub freq ) then it's +3db. Reason why when doubling amplifier power you only gain 3db ( 10log basis).

Anyway in your case Joris without studying circuit it's difficult to say.

 

[Newmarket]

To add to possible confusion it depend of what we are talking about too: if we talk about a voltage ( what happen within an electrical circuit) it's +6db for two identical source ( we are on a 20log basis).

If we talk about radiated power level ( from an omnidirectional source= loudspeaker below baffle step = low and sub freq ) then it's +3db. Reason why when doubling amplifier power you only gain 3db ( 10log basis).

Anyway in your case Joris without studying circuit it's difficult to say.

True. I think it's clear from the context of the question here that we are considering voltage (20logV1/V2) rather than power (10log...)

Apart from that, the concept of non-correlated signals becomes 'interesting' with much music program since there is often a significant degree of correlation between tracks, eg peaks happening at the same time.

 

[Barry Hufker]

I admit I always struggle with math and applying the correct dB formula (which is why I don't design anything, or build anything (except from kits). But I believe my explanation of the possible difference between a conventional analog mixer and a specialized DJ mixer to be a reasonable one -- until someone proves me wrong! Of course seeing a schematic will reveal all, as has been said.

 

[k brown]

Just spitballing here, but I woould imagine that DJ mixers are designed so that when crossfading from one song to another, the level remains constant.

 

[KrIVIUM2323]

Cross-fader is entirely different issue. But yes most of the time* they are 'constant power'.

*: with hip-hop oriented mixer ( scratch) the curve can be customised to full cut/on over a very small physical displacement. In that case it's not really constant anymore but much more a on/off rather than a curve. For more 'regular' dj ( 'Club music' were we can let tracks run by themself over multiple minutes) then curves are much more softer and allow subtle level variation. Eq are often 3 bands (with sometimes isolators) rather than the 2 bands found in hip hop desks. Broadcast desks are often the same but with 'start' tallies to drive decks when you open fader.

 

[Newmarket]

Just spitballing here, but I woould imagine that DJ mixers are designed so that when crossfading from one song to another, the level remains constant.

Something of a can of worms wrt crossfader laws tbh. Somewhat analogous to debate / options on panning. eg -3dB at centre...or not...

 

[Mihobro]

As long as they are not pegging there is no real concern here, just listen.

 

[Barry Hufker]

Just did some quick DJ Mixer research. This is an excerpt from the block diagram of the Pioneer DJ DJM-V10 mixer. A cursory scan revealed limiters in both the analog and digital outputs (with the choices of "on/off"). And a ducker ( called "talkover"). The "Digital Reference" is the user selection for the reference level with regard to 0dBFS.

 

[KrIVIUM2323]

Oh man, i never liked Pionner desk when they were analog, i shouldn't have ever took a look at this diagram! Lol.

As i'm old school and still use vinyl decks, here is schematic from my dj desk:

https://medias.audiofanzine.com/files/freevox-dj7-schema-470608.pdf

Simple no non sense circuitry.

'French touch' producers ( French EDM from mid 90's to 10's) often used this desk when performing live ( been installed in some Ibiza's Club at French's DJ request) and in studio(!). 'Disco Sound' function is a trademark from this whole scene sound.

Works very nice with style i play ('old school' -1995/2005- Drum & Bass).

Talk Over ( ducking) is a legacy from radio desks ( as are the 'start' function which in mine are 'integrated' into fader - there is a switch at minus infinity) . Can be nice when you have an MC ( not a cartdrige of cource but a 'Master of Ceremony'!). I never used it on mine though.

 

[Barry Hufker]

I don't mean it to be an example of exceptional quality, just an example of the digital processing in a random DJ mixer.

 

[KrIVIUM2323]

I agree it's in no way an example of quality imho!
But i'm hopeless, i still think digital is not for real time dj mixing. I'm a dinosaur! And proud about it. Allen and Heath ( analog) are modern great sounding dj desk imho ( vca used in there, psu rails at +/-15v and chanels with ample headroom ( +24dbu iirc), good sounding eq with powerful isolators- better with techno than other styles though imo-, nice ergonomic, not too much 'gadgets'....).

 

[Mihobro]

Please do not be satified with shoving all mixes into the same meter box. Different mixes, even different parts of the same mix should be set at different levels and adjusted by ear. And different meters will read different mixes at different levels, so a operator ultimately will have to adjust according to how it sounds. Master Christofori would be appalled. If you want consistency, listen to test tones not music.