sum to mono resistors and levels - dB ?

[Sleeper]

It's buried in a thread here somewhere, I've seen it...
but I just can't seem to find it :roll:
Maybe this would be a good piece to add to the mixers meta



Putting a mono switch into my monitor controller.
balanced 2k input impedence, balanced 2k out.

I want to keep levels from increasing when I sum to mono.
I'll need a small resistor network to drop a few Db,
but
how many DB should I drop?



I can figure out the resistors from NYDave's summing post and or tremaine
(I know some of you guys can do this stuff in your head, so feel free :grin

 

[rodabod]

Well, 6dB is electrically a double in volume, so I would suggest a 6dB drop for combining stereo to mono.

 

[alk509]

[quote author="rodabod"]Well, 6dB is electrically a double in volume, so I would suggest a 6dB drop for combining stereo to mono.[/quote]

By definition, a stereo signal is composed of two different signals, so they won't add up to the full 6dB when summed. I say 3dB.

Going once, going twice...

Peace,
Al.

 

[DrFrankencopter]

One speaker mono, or two?

For one speaker, I think you want double the power (6dB?). But for two speaker, keep it unity.

If its a purely passive summer I can't see how there will be a volume increase.....

Cheers,

Kris

 

[NewYorkDave]

The level should drop by 3dB (half power) when summing to mono, if you don't want the apparent volume to rise.

 

[Sleeper]

a stereo signal is composed of two different signals, so they won't add up to the full 6dB when summed. I say 3dB.

Going once, going twice...

Al you win.:wink:

The discussion was pretty lengthy, lots of opinion, but 3db is what I remember. I'll try that on my mono setup...
(I hadn't been sure if it was 3 or 4)

For one speaker, I think you want double the power (6dB?). But for two speaker, keep it unity.

I have 2 speakers in this setup, are you sure it should be unity. I don't get why.
Here's a new question.


IF
summing 2 signals causes an increase of 6db (or a realworld-i.e according to experienced engineers and designers- gain of about 3db)
AND
the way my switch works is essentially a sum, followed by a wye.
AND
this is kind of a perfect wye, since the load impedence should factor in the same no matter what position (regular stereo and summed mono to 2 speakers) it goes down the same cables to the same amps and drives the same speakers.

:?:
Is there any loss when making a wye?

How do you calculate that ?

Thanks
Sleeper

 

[Sleeper]

oh yeah, and while I was writing this, along comes New York Dave (i.e. realworld) for confirmation.
excellent.
Sleeper

 

[Kev]

see now I go with 6dB ... I am influenced by the IN sync sinewave
not by the two independant signals ... mutual coupling sort of stuff

but I have made simple systems for people that offer both options
and the ProTools virtual mixer has a strange pan sum rule ... 2.5dB

not easy to get three VU meters to evenly track from right to centre/mono to left and have the -20dBFS signal show 0dB left to 0dB right while the mono VU stays solid at 0dB

Practel SDA's allow you to , with plug-in trim boards,
set your own mono level.

I like SDA's for these VU meter driver and distribution jobs. Y cord and resistive divider and summers always seem to cause trouble in the long run.

 

[rodabod]

[quote author="NewYorkDave"]The level should drop by 3dB (half power) when summing to mono, if you don't want the apparent volume to rise.[/quote]

I don't quite undertstand this.... Can someone explain it to me?

As far as I knew, you would reduce by half power if you were at the speaker end. At your mixer, are you not simply dealing with voltage? I thought you would aim for half voltage (ie. -6dB).

Then, if two -6dB signals were reproduced, they would combine to form the same amplitude as a stereo setup?

 

[NewYorkDave]

The real-world answer is going to lie somewhere between, since a typical stereo signal is a mixture of correlated and uncorrelated information.

In terms of isolation--avoiding compromise of the individual channels--active summing is the best method to derive the mono signal, and in that case it's easy enough to adjust the levels experimentally to give the desired result.

 

[nacho459]

I've always heard it was +3dB when you go from panning hard left to center, cause you are basically double bussing. I always believed that doubling the power only raises the level by +3dB.

 

[Ethan]

[quote author="nacho459"]I always believed that doubling the power only raises the level by +3dB.[/quote]

With two sets of complex waveforms (like in the left and right of a stereo set) you will get +3 when summed. With two identical signals like a 1k sine wave you will get +6.

 

[zmix]

WARNING: ALTERNATE (possibly dissenting) OPINION
My custom monitor controller does not attenuate the signal when summing to mono.
And yes, I would have previously suggested that you drop 3db when summing.

-HOWEVER-
I added a "CUT Left" and a "CUT Right" switch to my monitor controller.

-SO-
When I switch to mono and cut one side, the volume does not shift at all!

-IN CONCLUSION-
If you want to properly listen in mono, do it using one speaker only.

 

[drpat]

...

 

[zmix]

drpat,
It's a real issue if you are listening for vocal level and the vocal level increases 6dB when you hit the mono button.

 

[drpat]

...

 

[zmix]

[quote author="drpat"]If that's the vocals are the only thing that increase by 6db when you hit the mono button, then you have bigger problems with your mix anyways. [/quote]I don't understand your false extrapolation, but perhaps I wasn't clear enough in what I intended to point out in my original post. I'll be more clear this time.
If the vocal is centered (which is a pretty typical placement), then summing the left and right channels will cause it to increase in level by 6dB.
When mixing, there is a specific SPL that I use consistantly when doing vocal rides -and I am typically making level changes on the order of tenths of a dB. If the summing changes the absolute level it can introduce uncertainty into the process.
Swiching to a single speaker while listening in mono is the best solution for me, but a variable dim on the summing function can also be very useful.

 

[drpat]

...