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, it is still under repair and the web hosting company has to fix something or I end up replacing them! 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 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:

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:

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6 thoughts on “Four weeks of Comb Stereo tests via WRMI!

  1. Andrew (grayhat)

    Tom, would it be possible to use the “audacity” sw (maybe with some plugin) to listen live (and record) the transmission with “comb stereo” ?

    1. TomL

      Not sure but I am fairly certain you have to run the live audio through the CSDecoder that Daz & Niall have provided in the instructions on It would seem more reliable to me to record the live broadcast to a mono MP3 file and then running that through the Virtual Audio Cable and CSDecoder. I could imagine something going wrong on the computer during a live recording, might as well record it as an IQ file first, but that is just me.

      1. Andrew (grayhat)

        I see, well I was trying to understand if it may be possible to perform the decoding in real time, in such a case it may then be possible to use (say) a RaspberryPI and an SDR dongle to put together a small autonomous receiver prototype

        1. Tom Servo

          I’m sorry, I misunderstood your initial question. You can decode live with comb stereo, it is not very processor intensive. You’ll need to select the virtual audio cable as your audio output source in the SDR software, and have the CSDecoder set up to take input from that virtual audio cable and output to your sound card, speakers or whatever you have.

          It’s not the easiest thing to get set up, but it’s the same process you’d use if you were decoding digital modes like FT8, MFSK32 or DominoEX with an SDR and Fldigi.

          1. TomL

            Thanks Tom Servo for filling in my gaps in knowledge. The older I get, the less patience I have for the small Linux computers and I only worked with a Windows laptop. Since the Virtual Audio Cable tends to take over the audio routing, it should work live to whatever the CSDecoder is pointed to. has a couple of test files to try (as well as their live Wednesday night 1 hour program). I guess the SDR software would be just another source input, just like a file, or a CD player.

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