Crosstalk Cancellation/Ambiophonics: Updated CTXMatrix Lite with standalone processor & 60° speaker angle support.

Significant changes in the UI from the previous CTXMatrixBeta release.

I want to remind 2-channel "immersive sound" lovers about the potential for using stereo crosstalk cancellation (XTC) / ambiophonics playback to enhance the 3D soundstage. You might have already heard of uBACCH in the audio magazines and on forums - why not try a similar effect for free (or through a small coffee donation)?!

You might recall, last year STC contributed a post on CTXMatrixBeta DSP for Windows. Well, it's great to see that he has continued to develop the software with updated user interface and abilities, this latest edition renamed CTXMatrix Lite, currently at version 1.3. It now includes a standalone processor which I'll spend some time discussing in this post, along with the 64-bit VST3 plugin as shown above that can be used in JRiver, Audirvāna and DAW software like Reaper.

Furthermore, there is now a VST3 plugin for Linux. Since I primarily use Windows for my music listening and processing, I'll stick with the Windows variant here with the hopes that some of this will be applicable. In my discussions with STC, he's aware of interest from Mac OSX users.

Perhaps the most important update in the last few months is that there is now improved support for standard ~60° stereo speaker angle (typically, the recommendation is 20-30° in ambiophonics). As a result, one should have a much better experience with the effect on most set-ups. In particular, hopefully more desktop computer music lovers will give this a listen without needed to move the speaker position and explore what you might be missing in your existing music library.

[If you run a miniPC streamer in the sound room like I do, CTXMatrix can easily be used like with HAF X-talk Shaper DSP discussed a couple years ago.]

IMO, the standalone processor is a nice addition to the package and will allow you to use whatever music player you wish by piping the audio into it through a virtual input/output loop. A free virtual loop driver to try is VB-CABLE. Download it, run the appropriate setup file (like "VBCABLE_Setup_x64.exe"):

Click on "Install Driver" and you should now see a device called "CABLE Input (VB-Audio Virtual Cable)" which you can point audio software like foobar2000 to use as the playback device:

Now run and configure the CTXMatrix Lite standalone app to accept the VB-Cable input, and configure output to whatever audio playback device or DAC you're using through the Settings window:

When you're sure you have no unpleasant audio feedback and ready to listen, unclick that "Mute audio input" box. For the other settings, I typically standardize my computer workstation at 48kHz these days; no need to futz around. Feel free to increase audio buffer size if needed.

Alright, now make sure to take some time to run through the calibration procedure as discussed here (the procedure was also touched upon in my previous post). Given the numerous variables involved including audio hardware, set-up geometry, and individual characteristics (eg. one's unique HRTF), getting the calibration right is essential for accurate-sounding tonality and spatial cues. It's an important bit of initial investment.

These calibration values work well for my ears on my
computer workstation with Emotiva Airmotiv B1+ speakers,
slightly toed-in. Speakers 55-60° angle from main seating position.

For convenience, let me copy over a chart from STC's documentation showing the approximate expected calibration values based on angle between where you're listening and the two speakers:

You'll get a taste of the effect if you start with the "baseline" dB and sample delay (smp) values. Best to calibrate of course while using those numbers as guide.

Once calibrated, in foobar (or whichever player you're using), go enjoy some music with crosstalk cancellation turned on!

"Balance" knob is an improvement from the previous individual L/R trim controls. I like having the "Center" knob to anchor the central image a bit better on some albums that might sound too diffuse (default is at 0). Use the level meters to make sure there's no clipping especially if you boost volume with "XGain".

In the same way as with foobar, I can point to the VB-Cable output as a Roon playback device:

With VB-Audio Virtual Cable, you'll typically see 2 outputs installed and listed in Roon, choose whichever has been mapped to your CTXMatrix setup; in my case it was the second.
For more see VB-Audio manual.

Good to have the "Bypass" button available to turn off DSP easily
since not everything will sound good with XTC engaged.
Hey Roon, why don't you guys implement XTC natively in your Muse DSP?
Among other obvious wish list items.

I was shocked by how different, in a good way, "Angel [Mad Professor Remix]" on Mezzanine: The Remixes (2006) sounded with ambiophonics processing! Likewise, acoustic albums like "Venus" off John Coltrane's Interstellar Space (1967) sounded like I was listening in a much larger space than just sitting in front of my computer in the home office thanks to the expanded room reverb "air".

Sometimes, studio productions like Michael Jackson's "They Don't Care About Us" on HIStory: Past, Present and Future, Book I (1995) can sound too much like you're wearing headphones with the music localized inside the head which I'm trying to avoid using loudspeakers. Fun experience I suppose for those who like that kind of effect, but I prefer to turn off ambiophonics with these kinds of recordings. Speaking of MJ, have a listen to "Thriller". The footsteps at the start should sound well-defined like they're walking across from right to left behind you; this is how it sounds in a multichannel rig with Atmos mix.

There are some albums that can really benefit from the ambiophonics DSP. For example, you might already have some QSound encoded albums (eg. Sting's The Soul Cages, Pink Floyd's Pulse, Roger Waters' Amused To Death, Paula Abdul's Spellbound), binaural ones (eg. Yosi Horikawa's Wandering, Jean-Michel Jarre's Oxymore binaural mix, Macy Gray's Stripped), or those intended to be immersive but downmixed like the stereo version of Justin Gray's recent Grammy-winning Immersed (2025, stereo DR9, multichannel/Atmos DR13) - check out the track "Tapestry". Listening through calibrated CTXMatrix likely will get you significantly closer to the intended surround effect these albums were aiming for.

Something else fun to try is to take multichannel/Atmos music downmixed to 2-channels and then run that through crosstalk cancellation. For example, the other night, I had a listen to BTS' new album ARIRANG downmixed from multichannel (higher dynamic range DR12 vs. stereo DR5). While not exactly the same as with surround speakers, you should still be able to appreciate the effect of the rear channel content with sound as if coming from behind your head (like in the track "SWIM"). Another multichannel album that surprisingly blossomed in CTXMatrix is The Cranberries' Everybody Else Is Doing It, So Why Can't We? (1993), check out "Dreams".

Finally, beyond music player software that can be configured, if you want all Windows audio output to go through CTXMatrix DSP, you can set VB-Cable as your output device in the System → Sound settings:

I'm told that CTXMatrix's Mode A/B/C settings are variations to the cancellation steps. I don't hear a big enough difference to have a preference.

As you can see, I'm enjoying Jon & Vangelis' "The Friends of Mr. Cairo" playing over YouTube in the Chrome browser, piped into CTXMatrix for the ambiophonics processing. Just as easily, I could be watching a movie with improved 360° soundtrack rendering.

Well done STC! Your DSP implementation of the RACE algorithm with ongoing improvements is a fitting homage to Ralph Glasgal's work bringing this to everyone. The plugin and standalone app has been stable over hours of listening and testing while doing work on my workstation computer. RAM usage not bad (~60MB max), and barely 0.1% CPU cycles at 48kHz during playback (AMD Ryzen 9 5950X machine).

Have fun music lovers and audiophiles! If you enjoy CTXMatrix Lite, go buy ST some coffee for his work. He might have saved you good money if you were thinking of purchasing the uBACCH plugin or even BACCH in general, as good as they might be and with advanced features.

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Let's end off with some new music.

As shown above playing in foobar, here's the recent track "The Mountain" (2026) by Gorillaz on the album of the same name:

The ending portion of the song (from 4:00 on) with the multiple overlapping voices saying "the mountain" sounds pretty cool with crosstalk cancellation turned on with each voice hanging in space with much greater width and depth.

As much as I love this album, my main complaint is that it's a sad, dynamically squashed DR5 stereo mix - even the 24/96 "hi-res" download is worthless when damaged like this! Given the complex layering of the production, it's a shame that the music is so unnecessarily robbed of breathing room, drowning out all the nuances. The louder portions are distorted, and low-level details get boosted to the point of just sounding gritty and fatiguing.

It's times like these when an audiophile needs to listen to the more dynamic multichannel/Atmos mix (DR10). 😏

Unfortunate dynamically compressed and distorted stereo mix above; HDTracks sells this as 24/96 "hi-res"! Do artists expect music lovers to buy badly damaged recordings?
I'll happily take the superior-sounding lossy 768kbps Atmos downmix any day - it's like a different recording sonically.

Happy Easter long weekend. Hope you're all enjoying some wonderful music!