RDS decoding with MNM4SDR (VLC, VB-Audio Hi-Fi Cable and RDS Spy)

Short Introduction

This is detailed instruction how to decode RDS information broadcasted by an FM radio station. I am using MNM4SDR program to control demodulation and streaming from remote Raspberry Pi with DVB-T dongle as low-cost SDR. Much more information about it you can find at MNM4SDR web site. But all of this is possible because of other great software such as:

• VLC Videolan
• RDS Spy
• VB-Audio Cable

You can also use popular Virtual Audio Cable (it costs 35USD), instead of VB-Audio Hi-Fi cable, but I am going to work with VB-Audio (It is Donationware!). There are two versions of VB-Audio, the first one is VB-Audio Virtual Cable but it cannot provide 192000 Hz sample rate We need to feed RDS Spy, hence You'd better skip it and go for VB-Audio Hi-Fi cable.

"Wiring" diagram

VB-Audio Hi-Fi Cable

I've prepared this instruction on my Windows 10 Professional and I believe It is going to work same way on Windows 8.1 and Windows 7 but no guarantees. The legitimate question is why do we need virtual audio card at all? Because, RDS Spy requires 192kHz sample rate audio on its input but unfortunately many audio cards cannot provide it. This is how audio playback and recording for the VB-Audio Hi-Fi cable should be set.

Figure 1. Setting for the VB-Audio Hi-Fi Cable

RDS Spy

 RDS Spy must be configured as it is on the Figure 2. Select "Configure" from the main menu then "Select RDS Source" (Configure=>Select RDS Source) and press "Sound card" button then choose Hi-Fi Cable output and check Direct RDS/MPX (192kHz)

Figure 2. RDS Spy setting

MNM4SDR and VLC

 As MNM4SDR hasn't got built-in media player I use VLC for the purpose but you can use what ever player you want that support FLAC Free lossless Audio Codec. I've tested Smplayer also and it works but the switching output audio is, in my opinion, less convenient. As it is shown at Figure 3. It is important to select sample rate 192000 and stream rate 192000 on the MNM4SDR.

Figure 3. MNM4SDR, VLC, VB-Audio Hi-Fi Cable and RDS Spy running together

In order to decode RDS VLC Audio device should be redirected to Hi-Fi cable input as you can see at Figure 4. As soon as you select Hi-Fi Cable as audio device You are not going to hear sound any more but, hopefully RDS information is going to show up at the RDS Spy.

Figure 4. Switching Audio device in VLC

That's it, You can now decode RDS and then switch audio device back to the speaker and listen to FM radio station