Stereo Summing to Mono

[Ken]

I have heard a good mono system only a couple of times but I was captivated.  A quote I picked up somewhere neatly describes my subjective response to the music with each format:
- stereo gives the illusion of "you are there"
- mono gives the illusion of "they are here"

I don't have a turntable or vinyl so I would be running digital files > DAC > amp.  There are some original mono recordings available in digital format but much of what I would like to listen to is only available in two channel stereo.  Which brings me to my question and outreach for advice:

Assuming appropriate resistors are in place to prevent back-feeding to the opamps of the DAC, can summed stereo give a reasonable approximation for mono?  I realize that so much depends on how the stereo recording was recorded, mixed, mastered, etc but in general terms is it a worthwhile consideration or will the mono output necessarily be substandard from a listener's point of view?

Edit:  I should also ask if anyone has experience using the stereo>mono conversion feature in such apps as Audacity.  How does that sound quality compare to the method I first described above?

[snoozzell]

it will give you an approximation of mono but depending on how things are mixed it can throw things out of balance.  For some modern stuff the mixer at least checks out how it sounds summed to mono because some clubs will play things in mono but it's usually an afterthought at best.

Summing will boost anything that is in both channels (center content) 6db.

Also if there are phase differences between the left and right channel (doubled instruments or vocals, stereo width phase effects) you will get comb filtering cancellations when you sum which can make things disappear from the mix.

So it technically works and there's no harm in trying it out, but you're going to have to get a turntable or find vinyl rips of mono albums if you really want good mono content.

Also I'm not certain but usually something like audacity is doing the same thing so I don't think the quality would differ between those two methods.

[Ken]

Thanks.  I agree that just forcing the two channels together via a passive resistor network would potentially create lots of problems, probably insoluble.  Also, I intuitively resist putting more devices in the analogue path between DAC and amp.

The advice I received from the Audacity forum was more encouraging.  I haven't tried this out but the advice was that Audacity reduces the level of each track by 1/2 when they are combined.  Theoretically the level and included noise should not then exceed the stereo level.  Also, apparently Audacity has a function to invert phase if that was necessary.

In all, it seems more logical to me to perform the summing/combining function in the digital realm.

[Ken]

Any comments about this possible solution, assuming an amp putting out about 5W per channel?  Sorry, not allowed to post an external link.

KEF CiTR-SM Stereo to Mono Adaptor

It inserts between the amp and the single speaker, apparently using some sort of transformer.

[Paul Birkeland]

That's more of a commercial office space product in my opinion.  It would be way better to do this at line level so you don't have to use a transformer.

You'd have to let me know the output impedance of your DAC and input impedance of your amp, as well as cable lengths and capacitances in order to recommend appropriate resistor values, but I've included an attached drawing that shows the arrangement.

[Ken]

Thanks Paul.  I have seen that sort of passive resistor network, with various R values, and one that had a 1:1 isolation transformer after the resistors.  My concern (without knowing if it's a valid concern) is would this sort of setup also sum the noise of the two channels?  Depending on how the stereo tracks were mixed, would there be phase issues?  Those concerns can be addressed (I think) by doing the summing in the digital domain, using some of the features of an app like Audacity.

The downside is that an Audacity solution would not be real time so not applicable to streaming from Tidal, etc; the resistor solution would be applicable there.

[Doc B.]

I am thinking more energy is being put into the what ifs than would be expended just trying a Y adapter and listening, or just setting your L and R speakers right beside each other or one on top of the other if they are small.

[Paul Birkeland]

would this sort of setup also sum the noise of the two channels?

What noise?  Do you hear noise now?

[Ken]

@DocB  Good point!  Try both and see what happens.

I was sort of fishing around (here and elsewhere) to see if/what other people had tried and what their experience has been.  Actually, it might end up being some of both - the resistors between the DAC and amp for streaming and the Audacity solution (without the resistors in line) for files I have downloaded on my computer.

[Ken]

One solution in the digital realm is contained in the subscription service provided by roonlabs.com which has a feature for real time conversion of stereo to mono, both from library files and streamed, with the ability to adjust gain separately for each channel and to invert the phase of either channel.

Seek and ye shall find

[Thermioniclife]

I am thinking more energy is being put into the what ifs than would be expended just trying a Y adapter and listening, or just setting your L and R speakers right beside each other or one on top of the other if they are small.

Simple yet elegant. KISS.

[2wo]

I especially like "Stack your speakers "...John

[Ken]

"Simple yet elegant. KISS."

I would have thought that brute force trial and error is the opposite of "elegant".