RNEI’s Comb Stereo and how to receive it

From April 2020 our broadcasts are 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). Daz has put a pretty good explanation on his page here about comb stereo if you’d like to learn more!

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

An example of Comb Stereo

Here is Fresh Start by Joakim Karud in broadcast mono.
Here is that exact same mono audio after being decoded.

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!

Setting up VSTHost with the decoder:

This guide assumes you have VB Audio Cable or similar installed, you can download it here
Step 1: Download VSTHost which is available here.
You can choose the version best suited to your system if you want but for simplicity we are going to download vsthostx86.zip. After downloading you need to unzip the file and run the exe.

You will also need to download the decoder VST file which is available here – Note: The combing method has changed 2020.04.08 and sadly is not backwards compatible, re-download is required if you have v6 or below!
Chrome is known to moan at you for trying to download it because it is not a commonly downloaded file, this is expected behaviour.
Once you have downloaded the VST, put it some place safe and out of the way.
I went to C:/Program Files/ and made a folder called DazDSP to put it in for this demonstration. Another good place is the folder you extracted VSTHost to!).

When you first open VSTHost you’ll be greeted with a message and then you will be at a screen that looks like this

Step 2: Add the decoder VST.
Firstly we are going to click file -> Set Plugin Path and choose where the Decoder dll file is (In this example it’s in C:/Program Files/DazDSP/)

Step 3: Add the plugin to the chain by clicking File -> Plugins -> RNEI Comb Stereo Decoder.
You can optionally open advanced settings by clicking the green settings button on the Decoder!

Step 4. Select an input and an output.
Here you will chose which device is putting audio into the decoder (Your microphone port or virtual sound card) and which device the decoder is outputting to.
You need to select 44100 as the sample rate and, to reduce stutter, we recommend choosing the biggest buffer size you can and selecting devices with the DS prefix if possible. If all worked, you’ll hear a little pop of it starting up!

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 undesired effect has disappeared, turn bypass off again and try adjusting the width slider to lessen the comb stereo effect!
    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 max (96k). Next go into windows sound settings and set the sample rate to 192k on both the virtual sound cards input and output. Doing this means the 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 fldigi and VSTHost at the same time 🙂