Since April 2020 our broadcasts have been encoded with Comb Stereo.

Before you read on, if you are currently listening to us, start a recording if possible so you can decode the stereo version later!

What is Comb Stereo?

Comb Stereo is an analogue stereo standard we have designed and programmed for sending stereo information over a mono only medium (like Shortwave). It was all started on the 30th of March 2020 with this conversation between Roseanna and Daz:

Our sound engineer, Daz, has a good technical explanation on his page here about comb stereo if you’d like to learn more!

A visual example: red = right and green = left.

Some examples of Comb Stereo

Here is Clouds by MBB encoded in Comb Stereo – This is a mono WAV.
Here is that exact same audio after being decoded with V7f6.
A clip of RNEI show #15 broadcast from WRMI with the V7g12 Comb Stereo Decoder

Decoding Comb Stereo

There are three main ways to decode Comb Stereo. In this tutorial we will cover option 1 and 2 in the chart below. Option 3 is quite simple but you may need to google for your audio software’s manual!

Downloading a VST Host with the decoder:

This guide assumes you have VB Audio Cable or similar installed if you are using an SDR, if you do not, you can download it here.
Step 1: Download our package of Pedalboard2 complete with the comb stereo decoders included.
Download CombStereo Pedalboard x64

Please note that the combing method was changed to v7 on 2020.04.08 and sadly is not backwards compatible. If you desire a decoder for older encoders please email us.

After you have downloaded and unzipped the file you’ll be greeted with a readme and 2 bat files.

We always recommend for you to read the readme.txt, but in simple the decoder will use your default audio in and output device. If you require it to be changed you can click on Options -> Audio Settings and change them in output & input

And that’s it, you’ve set up the decoder to work in real time!

If you want to test it and haven’t yet recorded or heard the show, you can download the mono file on this page, play it through your media player, tell your media player to output to the virtual audio cable and enjoy 🙂

Troubleshooting

  • If you are having any unpleasant effects with the decoder try sliding the bypass slider to “on”. This bypasses the decoder. If the unpleasant effects did not disappear when you turned off the bypass there is a chance your virtual audio cables are re-sampling poorly. We use VB Audio Cable and noticed this effect!
    To solve it, open the VB Audio cable control panel and set the sampling rate to 44.1KHz. Next go into windows sound settings and set the sample rate to 44.1KHz on both the virtual sound cards input and output. Doing this means any re-sampling is done by windows rather than the virtual audio cable software. It worked as a fix for us and hopefully will for you too!
  • Digital modes aren’t working properly after decoding? This is normal. Luckily, you can have your audio port or Virtual Audio Cable feeding both fldigi and a VST Host at the same time 🙂