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SDRunoPlugin_drm

The drm plugin for SDRuno is - as the name suggests - a plugin for decoding drm signals, as they are transmitted on shortwave.

DRM, Digital Radio Mondiale, is a form of digital radio. Transmissions are relatively scarce here in Western Europe, but is seems that elsewhere there is an increasing interest.

For DRM signals there are different Modes and Spectra, here is Western Europe transmissions can be received in Mode B, with a spectrum of 10 KHz. Other spectra are 4.5, 5, 9, 18 and 20 KHz.

Different Modes have different measures against fading in the signal.

The picture shows a reasonable signal on 9760 KHz, a transmission of the Radio Rumenia International, in Mode B, with a spectrum of 10 KHz. The waterfall clearly shows the effect of fading on the signal, the signal can be decoded however.

The picture shows that the receiver is tuned to 9760 KHz, that the samplerate is already reduced to 62.5 KHz (the decoder will do the further filtering an reduction to 12 KHz).

The decoder is - apart from GUI issues - a mirror of the decoder of the drm-receiver

There are no controls on the widget, as soon as the plugin is activated it will start reading in samples and trying to decode DRM.

A DRM signal is in one of 4 modes, Mode B is the one being decoded here. The spectrum is "3", telling that the qwidth is 19 KHz, symmetrically around 0.

The different labels in the widget give information on the reception. The name of the receiver service is "SNR Tiganesti E1".

On the right hand side of the widget, there are four labels, since the transmission can be decoder they are all green. From top to bottom

• the time sync label. DRM is transmitted using an (C)OFDM technique, what is important is that there is a time synchronization so that the receiver "knows" where segments in the incoming sample stream start;

• the FAC label. A DRM transmission contains data in the so-called FAC, i.e. Fast Access Channel. The FAC data is encoded as 4QAM, which is relatively easy to decode (given that the time synchronizaarion is OK). FAC data is concerned with structuring the data;

• the SDC label. The SDC, Service Description Channel, contains - as the name suggests - the description of the service, its name, how it is encoded, etc.

• the AAC label. The service is encoded in the Main Service Channel, and usually encoded as an AAC stream.

For each of these labels it holds that "green" means that processing is without errors.

The bottom line of the widget gives some quality indicators in a more quantitative way. From left to right:

• the quality of the FAC signal, expressed as number where higher is better;

• the quality of the SDC signal, expressed as number, higher is better;

• the quality of the AAC decoder, expressed as number, higher is better.

On the second to bottom line, we see the spectrum (3), the Mode (B), the encoding of the MSC (QAM16) and the way the audio is encoded (AAC).

The remaining labels give an indication of the frequency and time offset of the received signals. All labels are equipped with a tooltip telling the function.

Note that this version - other than previous versions - uses the fdk-aac library for audio decoding. The fdk-aac library supports both AAC and xHE-AAC encoded data.

The plugin is - as other plugins - developed under MSVC. Note that the plugin uses some additional libraries (dll's):

• libfdk-aac-2.dll, for the decoding of the AAC data

Note that running this dll requires two additional dll's

• libgcc_s_dw-1.dll
• libwinpthread-1.dll

Copies of these dll's is in the "the-dll" folder