Many people with large classical or jazz collections will have hundreds of mono recordings from the 1950s and earlier. These are often wonderful performances, but mono isn’t always the greatest listening experience, even using Roon.
This works by creating additional L + R surround channels from the mono mix, applying digital delay and phasing, then remixing the 4 channels back to 2 channel “ambient stereo” for headphone listening. Works like magic! Every mono recording is now enhanced with stereo width, although of course you don’t get the “soundstage” from genuine stereo. And you can adjust apparent room size (I used 25ms delay for classical), “wetness” of the mix etc. as you require. Example of the signal path is shown below.
Use the mixer to create the additional virtual surround channels. To retain the existing main mono mix, I also swapped R and L - otherwise had issues with cancellation effects on mix down.
Now the two new virtual channels need a high pass filter (150hz, slope of 12db per octave). Note that this is JUST for the surround channels - you want to leave the original mono mix alone.
Now you need to add delay. I chose 25ms for large scale classical music, but YMMV. Smaller rooms and jazz clubs probably need 10-15ms. I am still experimenting with this. I really don’t like the “swimming pool” effect when the reverb overwhelms the main mix, as with the early digital delay processors.
Finally, you need to mix your two virtual channels back into the main mix AND invert the phase on one of the rear virtual channels - this creates the stereo ambience. It also allows you to use Dolby Surround if you want to play your mono albums on the main system.
For the final mix, I currently mix the two virtual channels back in at -6db (so 25% as loud as the original main mono channels), but -10db is also subtle but quite effective.
I found with this identical chain, the sound “pulled” strongly to the right channel, so I wound up reducing the final mix (right > right) to -9 to counteract, which then sounded “balanced” to me.
Interesting. One of the complexities of the original chain is that I had to swap L and R channels at the start of the mix. When I was experimenting with different settings, I had a similar issue, although I can’t remember the exact cause. However the processing chain I showed on the screenshots is providing me with balanced volume in L and R channels, and I have lowered the surround volume to -10db and reduced the delay to 20ms for more realistic ambience. Also swapped back the L and R channels in the final mix.
Hi John. I think I may have found the issue. Mono recordings can either be encoded as single tracks or as identical stereo tracks. All my early testing was on mono CD rips which had been encoded as identical stereo tracks, and this worked fine. As soon as I tested a single mono track, I got the exactly the same problem that you reported - it is either fully R or L. However, this is easily fixed by adding an extra mix stage at the start of the chain which feeds both channels. Screenshots with the additional mixer settings are shown below. Good luck!
Agreed. It would also be really helpful to have Roon provide some standard “presets” which help the non technical Roon user get the most from the product. This could include basics like Mono as well as Ambient Stereo, and some more headphone settings apart from Audeze. Perhaps a future Roon release will include more user-friendly functions (we hope).
@danny Is this worth adding somewhere in the Roon Knowledge space? Would also love to see preset DSP buttons for Mono, Ambient Stereo etc. as part of the future UI roadmap. Still loving the Roon product - this approach enhances user experience using existing core functionality.
