Result of gain and clipping off Passive Summing mixer

[tjcinnamon]

I’m looking at getting one of these passive mixers to do some elaborate summing of signals and inverted signals (notably the left and right signals): https://www.sweetwater.com/store/detail/Mix21--radial-mix-21

I’m setting up a Denon AVR to send RCA pre-outs (2v) to the Mix 2:1 with a RCA to XLR cable. Will I need to attenuate the signals prior to summing the stereo signal to avoid clipping?

Secondly, will there be any loss in gain because I’m using RCA to XLR?

 

[rationaltime]

I have not seen the Radial Engineering Mix 2:1, but I have several Radial interface boxes.
They are well made.

For reference, the Radial 2:1 mixer

No, you with 2V signals from your AVR you will not have clipping before or after summing.
The attenuation knobs allow setting the level of each channel.

No, in this case you will not lose gain using unbalanced inputs. However, I would be cautious
in the choice of cable or adapter. A cable with RCA male to XLR male connectors might short
the ground pin to the negative signal pin. That would preclude using the ground lift if you
need it. I might make or buy RCA to TRS with the signal going to the T and R connections.
The S (sleeve) connection can be wired to the cable shield at the one end, but should not be
connected to the signal. By unscrewing the TRS barrel it is easy to check the signal routing.

All right, now I have a question. Most source material is two channel. In simplest form this is
combining stereo channels to mono. Do some surround sound audio visual receivers internally
provide the mixing function (perhaps with equalization) you request? If not, you might also
search for monitor controller or studio controller just to see if some other choices are attractive.

 

[tjcinnamon]

I have not seen the Radial Engineering Mix 2:1, but I have several Radial interface boxes.
They are well made.

For reference, the Radial 2:1 mixer
View attachment 342048

No, you with 2V signals from your AVR you will not have clipping before or after summing.
The attenuation knobs allow setting the level of each channel.

No, in this case you will not lose gain using unbalanced inputs. However, I would be cautious
in the choice of cable or adapter. A cable with RCA male to XLR male connectors might short
the ground pin to the negative signal pin. That would preclude using the ground lift if you
need it. I might make or buy RCA to TRS with the signal going to the T and R connections.
The S (sleeve) connection can be wired to the cable shield at the one end, but should not be
connected to the signal. By unscrewing the TRS barrel it is easy to check the signal routing.

All right, now I have a question. Most source material is two channel. In simplest form this is
combining stereo channels to mono. Do some surround sound audio visual receivers internally
provide the mixing function (perhaps with equalization) you request? If not, you might also
search for monitor controller or studio controller just to see if some other choices are attractive.

Thank you so much for taking the time for the response.

The AVR does not offer any controlled summing.

My goal is to basically end up with 3 channels at the end: summing Left and Right; summing inverse left with right; summing inverse right with left. So I’d have 3 of these devices outputting to 3 inputs on a power amp.

The reason I ask about the summing causing clipping is because if I’m summing Left and Right, where they overlap essentially would be 6dB higher. So it would stand to reason to reduce the Left and Right by 3dB to compensate sounds that would “double”. But perhaps there’s compensation built in. Or maybe it doesn’t work like that in the analog domain?

 

[rationaltime]

The Radial Mix 2:1 has enough range to accomodate those 2V signal levels.

You are right. It does work like that in analog.
Adding a little clarity, call
combined = left + right
If we want half of combined (-6 dB) then
combined/2 = (left + right)/2 = left/2 + right/2
In other words -6 dB on left AND -6 dB on right

I doubt the levels are critical, more like adjust by ear.
Let us know how it sounds.

 

[tjcinnamon]

The Radial Mix 2:1 has enough range to accomodate those 2V signal levels.

You are right. It does work like that in analog.
Adding a little clarity, call
combined = left + right
If we want half of combined (-6 dB) then
combined/2 = (left + right)/2 = left/2 + right/2
In other words -6 dB on left AND -6 dB on right

I doubt the levels are critical, more like adjust by ear.
Let us know how it sounds.

So reduce the signal by 6dB on each channel for the combined channel to achieve the original volume?

And I’ll definitely let you know how it sounds!

 

[DVDdoug]

You can't actually sum signals passively (assuming a normal setup with a common ground). If both outputs are 1V the most you can get is 1V. If you "sum" 1V & 0V, the most you'll get is 1/2 volt. If the signals are out-of-phase they can sum to zero (silence).

You also can't invert unbalanced signals passively. So you can't subtract (unless they already happen to be out-of-phase when you sum).

You CAN get subtraction by sending the left and right "incorrectly" into a mono balanced connection. It's easy if you have a balanced TRS input by using a Stereo TRS to RCA adapter. If you have XLR inputs you'll also need a TRS-to-XLR adapter. Or you can invert a signal by using just the left or right with a "stereo" TRS adapter, again using it "incorrectly" into a single-mono input.

If you can build electronics it's not too hard to make inverting/summing, and subtracting (differential) circuits with op-amps. And these will truly sum (1V + 1V = 2V). A million years ago in the days of "quad" and before Dolby 5.1, I made a left-right subtraction gizmo to make a crude surround setup.

You can also use Audacity to make audio files with addition (mixing), subtraction, inversion, etc. So of course the files have to be processed in advanced of playback and if you want multiple channels you'll need a surround setup.

 

[tjcinnamon]

You can't actually sum signals passively (assuming a normal setup with a common ground). If both outputs are 1V the most you can get is 1V. If you "sum" 1V & 0V, the most you'll get is 1/2 volt. If the signals are out-of-phase they can sum to zero (silence).

You also can't invert unbalanced signals passively. So you can't subtract (unless they already happen to be out-of-phase when you sum).

You CAN get subtraction by sending the left and right "incorrectly" into a mono balanced connection. It's easy if you have a balanced TRS input by using a Stereo TRS to RCA adapter. If you have XLR inputs you'll also need a TRS-to-XLR adapter. Or you can invert a signal by using just the left or right with a "stereo" TRS adapter, again using it "incorrectly" into a single-mono input.

If you can build electronics it's not too hard to make inverting/summing, and subtracting (differential) circuits with op-amps. And these will truly sum (1V + 1V = 2V). A million years ago in the days of "quad" and before Dolby 5.1, I made a left-right subtraction gizmo to make a crude surround setup.

You can also use Audacity to make audio files with addition (mixing), subtraction, inversion, etc. So of course the files have to be processed in advanced of playback and if you want multiple channels you'll need a surround setup.

Oh, I don’t mind if it doesn’t get louder. I just don’t want it to clip. My plan so far is to use the Invert button for subtraction.

I’ve been experimenting with Audacity and when it uses the “convert stereo to mono”reduces each channel before combining.

I want to use this for all signals coming out of the pre-outs of my AVR into my power amp. The goal is to have reduce interaural crosstalk using phase cancellation while not requiring a phantom center. So with 3 speakers the middle is the “phantom” center and the left and right are regular and inverted signals.

Unfortunately, I’m terrible with electronics and this box seems to do all the things I’m looking for (summing and inverting).

 

[tjcinnamon]

You can't actually sum signals passively (assuming a normal setup with a common ground). If both outputs are 1V the most you can get is 1V. If you "sum" 1V & 0V, the most you'll get is 1/2 volt. If the signals are out-of-phase they can sum to zero (silence).

You also can't invert unbalanced signals passively. So you can't subtract (unless they already happen to be out-of-phase when you sum).

You CAN get subtraction by sending the left and right "incorrectly" into a mono balanced connection. It's easy if you have a balanced TRS input by using a Stereo TRS to RCA adapter. If you have XLR inputs you'll also need a TRS-to-XLR adapter. Or you can invert a signal by using just the left or right with a "stereo" TRS adapter, again using it "incorrectly" into a single-mono input.

If you can build electronics it's not too hard to make inverting/summing, and subtracting (differential) circuits with op-amps. And these will truly sum (1V + 1V = 2V). A million years ago in the days of "quad" and before Dolby 5.1, I made a left-right subtraction gizmo to make a crude surround setup.

You can also use Audacity to make audio files with addition (mixing), subtraction, inversion, etc. So of course the files have to be processed in advanced of playback and if you want multiple channels you'll need a surround setup.

I meant passive using this box which doesn’t require power not plugging two things into the same cables.

Perhaps I made things confusing

 

[rationaltime]

You can't actually sum signals passively (assuming a normal setup with a common ground). If both outputs are 1V the most you can get is 1V. If you "sum" 1V & 0V, the most you'll get is 1/2 volt. If the signals are out-of-phase they can sum to zero (silence).

You also can't invert unbalanced signals passively. So you can't subtract (unless they already happen to be out-of-phase when you sum).

You CAN get subtraction by sending the left and right "incorrectly" into a mono balanced connection. It's easy if you have a balanced TRS input by using a Stereo TRS to RCA adapter. If you have XLR inputs you'll also need a TRS-to-XLR adapter. Or you can invert a signal by using just the left or right with a "stereo" TRS adapter, again using it "incorrectly" into a single-mono input.

If you can build electronics it's not too hard to make inverting/summing, and subtracting (differential) circuits with op-amps. And these will truly sum (1V + 1V = 2V). A million years ago in the days of "quad" and before Dolby 5.1, I made a left-right subtraction gizmo to make a crude surround setup.

You can also use Audacity to make audio files with addition (mixing), subtraction, inversion, etc. So of course the files have to be processed in advanced of playback and if you want multiple channels you'll need a surround setup.

What happens if you drive one of these from the right side?

 

[tjcinnamon]

I received a response from Support and it looks like unbalanced to balanced and back again isn't a big deal. Also, it looks like they already attenuate 6dB to account for the sum clipping when joined:

"Since the Mix 2:1 is designed to accept high amounts of signal without clipping (i.e. > +20dBu), you should not have to attenuate the inputs at all before connecting them to the Mix 2:1. As for your second question, the only change in output level that will occur is an inherent 6dB of signal loss that is tied into the design in order to accommodate for the amount of excess output level that is gained when summing balanced stereo connections together to mono. Since you’re using the Mix 2:1 with unbalanced signals, that overall amount of attenuation that occurs might change a bit, but overall its an amount that should be able to be easily accommodated for elsewhere in the signal path."

So I think this is my direction.