Converting lower frequencies to mono

Do you guys have a lot of stereo bass instruments? I only have kick and bass guitar usually and since those are both mono sources, they get centered naturally..

Collapsing LF to mono doesn’t make sense to me, the idea that LF is “mono” ( nobody has ever been able to point me at a corner freq for this effect) is more a function of the simple radiation effect where once the wavelength is greater than the dimension of a baffle it radiates Omni and as the frequency goes down the wavelength increases so as long as 2 or more radiating surfaces are within 1 wavelength they acoustically sum. LF summed to mono sounds weird if it isn’t naturally filtered, the higher harmonics that serve to give directional cues are still stereo. ( why stereo subs work sooo much better than mono).

Yeah I grew up as a live guy in the age of the separate LF mono aux craze, but I was also the guy tasked with figuring out how to make it musically integrate with the mains and the rest of the subs ( lots of drive rack tweaking and a drive rack matrix).

Doing a lot of live work I frequently have large stereo low frequency mud that, while adding ambient excitement, clouds the entire image and is improved by going mono on those sources below certain frequencies. Once it bounces off the walls and comes back, it’s definitely not mono!

In the world of orchestras in large spaces, there's a considerable amount of stereo information at low frequencies.  Objectively this sounds better and enhances your perception of spaciousness.  But in the world of vinyl mastering, all of those low wavelengths were often out of phase and could kick the cutter out of the groove when mastering.  And even if you managed to get some of that onto a disk, it was sometimes hard to keep the repro stylus in the groove.  Many of my vinyl memories include the quarter taped to the top of the head shell.  I was clearly not--and am still not--a fan of vinyl. At any rate, taking the lowest frequencies down to mono keeps those low waveforms in phase.  The stylus rides up and down instead of wildly back and forth.  This became part of the vocabulary of mixing, especially in more commercial forms of music.

I think there's the secondary detail that having the lows in mono gets that signal onto two speaker cones instead of just left or right.  This is helpful if the audio system is a little challenged.

When those old recordings began to be repurposed for CD, things were occasionally taken in the opposite direction.  Whatever phase differences still remained at lower frequencies could be exaggerated in the effort to restore some of that spaciousness.  Needless to say, you had to be really careful.

when doing mix/masters for my band The Shea the vinyl plant told me that everything under ~120Hz needs to be mono to prevent vinyl cutting problems. so yeah it can be important.
and i made it a habit now (even if i only mix for digital release) to keep bass in check by mono-ing it. frequency depends on the instruments. most of the times i do around 90Hz.it sounds cleaner, more compact to me.

Thanks for all the replies. I'm still toying with Basslane Pro and trying to see what else I can do with some of the other stuff out there. Basslane Pro definitely has a lot more you can do with it than Monofilter or Ozone Imager. So far, it's a lot better for me than Goodhertz mid-side. These I used only in mastering. I took BP off my sub-mix auxes and used the Fusion stereo imager plugin instead. Then used BP on the mastering with MDWDRC2. It can radically change your master, the widening function does a lot and I don't think it's making it any worse. This after I had already treated it with Fusion with minimal use of the stereo imager section. Best stuff I've done so far. When I was using the monomaker on Amek console from PA, I had the stereo imager on a lot. At this point, I would say BP is far better than those PA functions. But I'm just using presets now since the limitations of the trial version would force me into writing things down or taking pictures like I have to do with Fusion. I'm not sure I would want to convert a lot of frequencies to mono without also expanding the image some. A lot to learn here...

This.  Exactly.  Take a listen to "Glass Onion" by The Beatles in headphones.  If they could cut low end that way in the 60s then they can do it now.  Vinyl companies like to try to make things easy for themselves.  

Respectfully, let's just a moment for some math/s questions

1. Low end is what? 20-100hz?
2. Any higher?
3. Ok what is the wave length of a 20hz wave?
4. How about a 30, a 40, a 50 and so on . . . ?
5. Stereo on anything below 50hz stays stereo for (about 15 milliseconds) how long? (before it goes omnidirectional)
6. What happens to it then?
7. Is there a possibility of phase cancelation with two competing sources of the same program material?
8. Is it better to let every room the material is heard in choose how the bottom will bloom, or should you decide for yourself?
9. And why is your answer to 7 better?

Answer the old geezer's questions and then let's talk to Vicious Bliss again.

I sometimes go the opposite way and try to make the bass guitar have some stereo width by sending some signal to a Roland Dimension D or similar effect
albeit high passed to some degree to stop it sounding muddy.

1. Low end is what? 20-100hz? 2. Any higher?
Close enough

3. Ok what is the wave length of a 20hz wave?  4. How about a 30, a 40, a 50 and so on . . . ?
Trick question.  Wavelength depends on the medium.  But the calculation is easy if you think in frequency terms.  The period for a complete cycle comes from dividing 1000 by the frequency in Hz.  So a 20 Hz sine wave will have a period of 50 ms.

5. Stereo on anything below 50hz stays stereo for (about 15 milliseconds) how long? (before it goes omnidirectional)
No reason for it ever to go omnidirectional (which isn't quite the right term).  A signal of any frequency is likely to lose its sense of direction over time, but that doesn't mean it's the same in all channels. See the next answer.

6. What happens to it then?  7. Is there a possibility of phase cancelation with two competing sources of the same program material?
Phase cancellation is unavoidable in a real space.  The distance to any reflecting surface is unlikely to be a perfect multiple of a wavelength, so the bounces will cause some cancellation.  But the key thing is that there are thousands of cancellations going on all at once.  The average frequency response in a decent space will remain remarkably consistent.  This sort of very common phase cancellation has another name: reverb.

8. Is it better to let every room the material is heard in choose how the bottom will bloom, or should you decide for yourself?
I think not.  It's always best to mix in a neutral room. Proper calibration in the listener space is pretty rare, but whenever it does happen, the response should be in the rough neighborhood of what the mixing space gave you. Outside of that, there's not really a way to compensate at that late stage in the chain.

9. And why is your answer to 7 better?
Because it's a truthful answer ;-)

In my first response on this thread, I wasn't intending to render an artistic opinion on low-end mono. That's up to the discretion of the mixer and/or producer. I just wanted to give some context on why vinyl mastering engineers prefer it. They're simply trying to make a disk work on the broadest set of turntables they can. It's true that a number of recordings from the 60s had stuff spread all over they place. But it's also been made clear by George Martin (and later Giles Martin) that the intent was mono and the labels forced them to spread stuff around--even when it didn't make a whole lot of musical sense. I had a Parlophone pressing of Sgt Pepper back in the day and it hopped around on every turntable I tried it with. I'm quite sure it was the LF stuff going out of phase and kicking the stylus out.

The artistic choice to do this can be an interesting one. Normally, given what I do, I prefer that natural width that can come at low frequencies. But just a few days ago, I had a concert to master with kick drums in a chamber music piece. Two drums, played by two players were both on the same side of the soundstage. It sounded horrible. So I used the multiband imager in Ozone to mono-ize the LF and get most of the drum energy back in the center. Not natural in this context, but absolutely necessary. You'll sometimes hear a lot of hooey about us classical guys being purists of some sort. We just want to seem like purists ;-)