Tag Archives: Comb Stereo

Reminder: Comb Stereo Broadcast via Radio Gum Tree–June 18, 2021

A quick reminder that the rebroadcast of Radio Gum Tree Episode 2 will take place tomorrow: June 18, 2021 at 9:45 EDT (or June 19, 2021 at 01:45 UTC) on on 5850 kHz. You can find the program notes for these Test broadcasts at this web site address: www.radiogumtree.com/?p=54

Many thanks for putting together this Comb Stereo series, TomL!

For more information, check out TomL’s initial announcement.

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More Comb Stereo Broadcasts via Radio Gum Tree June 18 & 25, 2021

Many thanks to SWLing Post contributor, TomL, who notes:

Episode 2 of Radio Gum Tree will be rebroadcast this coming Friday night June 18, 2021 at 9:45 EDT on on 5850 kHz in case anyone missed it. Episode 3 should be on June 25.

You can find the program notes for these Test broadcasts at this web site address. I will not be archiving the broadcast on the internet due to music copyright concerns.


Many thanks for putting together this Comb Stereo series, TomL!

For more information, check out TomL’s initial announcement.

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Four weeks of Comb Stereo tests via WRMI!

Many thanks to SWLing Post contributor, TomL, who has put together a four week series of Comb Stereo tests that will be aired on WRMI. Here’s the full announcement:

Starting this Saturday June 5 at 01:45-02:00 UTC (Friday 9:45pm EDT), I will be conducting a four-week series of tests using Comb Stereo. The broadcast will be aired on WRMI on 5850 kHz and will only be 15 minutes long. It will feature two minutes of “CNN” news by a computerized voice (sorry, I am doing this on-the-cheap!). Then, what follows is about 12.5 minutes of music encoded with Comb Stereo.

For you, the listener, to hear the Comb Stereo, you will need to record the broadcast to your digital recorder or SDR software and then play it back through your Windows PC using the instructions at the bottom of this announcement. I welcome feedback regarding such things as, 1 – I heard the broadcast and recorded it, 2 – I tried to setup my Windows PC but could not get the CSDecoder and Virtual Audio Cable to work, 3 – I got those things to work and opinions about what the stereo sounded like.

To repeat, you will not hear stereo unless you send your recorded audio file through the CSDecoder.

Do not expect FM Broadcast quality since Comb Stereo is a rudimentary form of creating two-channel sound. For instance, you may hear the stereo separation waiver a bit, or the sound stage image may wander, or a slight hollow sound at times. Sure, OK, but this is also a chance to hear stereo from a shortwave broadcast. So let me know your thoughts by sending feedback to [email protected] and I will tally up the results and post the findings here on the SWLing Post Blog.

Many thanks to Daz and Roseanna at Radio Northern Europe International for making the Comb Stereo available and to WRMI for the use of their transmitter.


P.S., please don’t mind the look of the web site at www.radiogumtree.com, it is still under repair and the web hosting company has to fix something or I end up replacing them!

RadioGumTree.com is a personal, eclectic look at Radio, Music, the Universe, and Beyond. For feedback or questions, please write to [email protected]. For program notes, please visit the Blog section of radiogumtree.com for more details.

The broadcast itself will not be archived on my web site due to copyright concerns.

For Radio episodes that are encoded in Comb Stereo, go to this web site for instructions on how to install the Comb Stereo decoder: https://rnei.org/stereo/

For an example of a guided user install of CSdecoder and the needed Virtual Audio Cable on your Windows PC, go to this blog post: https://swling.com/blog/2021/05/guest-post-listening-to-comb-stereo-on-shortwave/

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Guest Post: Listening to Comb Stereo on Shortwave

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:

Comb Stereo on Shortwave

by TomL

Comb Stereo is an old technique being implemented over shortwave by the main sound engineer (Daz) at Radio Northern Europe International (RNEI).  It ONLY works on Comb Stereo broadcasts which currently are RNEI, This Is A Music Show (WRMI), and one of the KBC broadcasts.  It works in real-time or for SDR recorded files, too.  It does NOT need a special HD/DAB+ radio.

A number of pluses for Comb Stereo on shortwave compared to digital:

“The bandwidth is the same as mono – So the SNR should be about the same as mono.

Selective fading doesn’t affect the comb bands much, so the balance is largely unaffected by selective fading notches.

The Comb Stereo artifacts are much like typical music effects of echo, chorus, fast reverb or room reflections.”

You can read about it here on Daz’ web site: homepages.ihug.com.au/~daz2002/tech/CombStereo/

You can also read Roseanna’s comment on the SLWing.com blog post: https://swling.com/blog/2020/04/rnei-now-broadcasting-in-comb-stereo/

An enhanced version is broadcast on WRMI for the RNEI time slot on Thursday morning (01:00 UTC) on 5850 kHz.  It sounds very good and is not a pseudo-stereo like in my previous article, Music on Shortwave.  For one thing, pseudo stereo is not real two-channel encoding and shifts vocals to one side, depending on which channels are chosen for high and low filters, which might get annoying after awhile.  What seems amazing to me is that I have been able apply some minor noise reduction in Audacity and the Comb Stereo stays perfectly intact.  It also still works after converting the WAV file to MP3 and sounds much like a regular FM broadcast.  Furthermore, it does not require a special patented transmitter or receiver chip.  It is compatible with regular mono transmitters.

If you want to try it, go to the RNEI web site; download and install the two files listed (VB Audio Cable and CombStereo Pedalboard x64):


It is slightly tricky to setup and use or you will not hear anything (most Windows systems default to 48000 Hz these days).  Right-click on the lower-right taskbar Sounds settings.  Make sure to setup Properties – Advanced in both the VB-Audio Virtual Cable (Playback and Recording) and your output speakers (Playback) to 24-bit 44100 Hz processing.

Now run the app Pedalboard BAT file which corresponds to the broadcast you recorded (in this example “Start Comb Stereo for WRMI.bat”).  Set the Options – Audio Settings:

Since the VB-Audio Virtual Cable takes over your volume output, adjust the volume of your Speakers in Windows’ Sounds – Levels (or you can adjust the volume in the sound player you are using, too):

Play the mono WAV or MP3 file and you should be hearing stereo!

When you are done, close Pedalboard2 and then disable the VB-Audio Virtual Cable for Playback and Recording to get your Sounds back to normal:

I cannot demonstrate what it sounds like unless you have the VB-Audio Virtual Cable and the Comb Stereo app setup and working properly.  Here are snippets from recent RNEI broadcasts captured by my noisy porch antenna:


Here are links to the artists’ YouTube videos for comparison:

Kari Rueslåtten – https://www.youtube.com/watch?v=SFN4O3YrUG4

Ani Glass – https://www.youtube.com/watch?v=T63QS9enT-A

What is nice is that I can create a space-saving MP3 mono file and this setup will decode the stereo when run from the computer (sounds really nice on a stereo system with a subwoofer).  Unlike digital, this analog-friendly stereo seems mostly immune to fading, has a minimum of digital artifacts, and will not go silent and “drop out” like digital does for long, annoying periods of time.  It is not perfect stereo but audio players with features like Stereo Widener or Windows Sonic for Headphones can overcome some limitations.  Perhaps content providers should consider Comb Stereo for all their shortwave radio shows since it is perfectly compatible with mono AM transmissions!

Enjoying the Music,


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Radio Northern Europe International update and May 2020 broadcast schedule

Many thanks to SWLing Post contributor, Roseanna, who shares the following announcement from Radio Northern Europe International:

Hello everyone,

Last broadcast was pretty successful with many wonderful reception reports and some people sending in decodes of the stereo which is amazing to hear!

A reminder to go to https://rnei.org/stereo/ to learn how to decode the stereo, it is real stereo over a mono shortwave transmitter!

RNEI show 4 is half dedicated to Eurovision entries so the first half of the show is an entery from each Nordic country and after that we take a trip to some Faroese and Irish traditional musics before ending with our favourite Eurovision entry from this year and the final song containing the MFSK 32!

TIAMS has made another 30 minute express music show for after our broadcast for you to enjoy!

Click here to continue reading the announcement and view the full RNEI schedule.

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RNEI now broadcasting in Comb Stereo

Many thanks to SWLing Post contributor, Roseanna, who shares the following announcement from Radio Northern Europe International:

Hello everyone,

The show is finished, transmitter time booked and pre-processing done so it’s time to announce RNEI #3 & TIAEMS April 2020 to all of you!

Before we continue, we need to announce something pretty special and unique about this and future RNEI broadcasts:

RNEI is now broadcasting in Comb Stereo. It’s a standard we made and it’s a really nice addition to having a mono only broadcast. It’s easy to decode and it doesn’t degrade the mono signal!

For more information about the system and how it is decoded please see https://rnei.org/stereo/

RNEI #3 features 30 minutes of our favourite music from all over Northern Europe; Sweden, Finland, Norway, Denmark and Iceland this show. I’ve really enjoyed choosing the music and putting it all together, I really hope you enjoy listening to it.

We will also have the playlist sent in MFSK32 embedded into the final song, very similar to show #1 (we’ve worked extra hard to make it as hidden as possible which was a massive challenge this time, it’s in 2 parts during the final song with an RxID at the start of the final song).

Just like last month, TIAMS has been kind enough to join forces and make us a 30 minute express version of his show which I have loved listening to and I’m sure you will love it too![…]

Click here to continue reading the announcement and view the full RNEI schedule.

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