Digital Audio Question

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jimmyjon

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Can somebody help me figure out what this audio is that is coming over my local police frequencies.

I currently have a RTLSDR setup with SDR# most of the auto that comes through the police frequencies is analog voice but every now and then I get something that sounds like digital voice. But when I send the audio to DSD+ it does not decode the audio.

Here is a snippet of the audio.

Zippyshare.com - DSDPlus-Raw-Input_2014-10-04@171535.wav

Thanks
 

Ghstwolf62

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Could privacy or encryption be enabled on it?

That would pretty much screw picking it up.

I have Nexedge out here and the DSD+ doesn't say anything about privacy or encryption being active yet it is. All DSD+ shows in the RAN and NX96 plus of course TGs, names and RIDS.

Not sure how Mototrbo shows up in it since I don't have any near by I can pick up right now.
 

jhampton2000

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That does not sound like MotoTRBO to me at all. The closest I would put it to is Nexedge 9600, but the 'tail' on the end of the transmission makes it sound like it is trunked (I've not come across NXDN9600 Trunked before to give you a definitive answer).

So from what you describe, you are hearing this on a frequency that you don't expect - right? And since DSD+ isn't decoding it, I'd say it ISN'T being transmitted on the freq you are tuned to, and that it's intermodulation from a nearby frequency. The signal could be of such poor quality DSD+ can't touch it. I'd try and find what freq it's actually on, tune to that, and see if that decodes ok.

Encrypted P25 will decode in DSD+ but it mutes the audio. Encrypted Nexedge and MotoTRBO will also decode, but the audio will come through as scrambled. The event log of DSD+ shows the channel to be Enc for TRBO, but doesn't for Nexedge.
 

jimmyjon

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That does not sound like MotoTRBO to me at all. The closest I would put it to is Nexedge 9600, but the 'tail' on the end of the transmission makes it sound like it is trunked (I've not come across NXDN9600 Trunked before to give you a definitive answer).

So from what you describe, you are hearing this on a frequency that you don't expect - right? And since DSD+ isn't decoding it, I'd say it ISN'T being transmitted on the freq you are tuned to, and that it's intermodulation from a nearby frequency. The signal could be of such poor quality DSD+ can't touch it. I'd try and find what freq it's actually on, tune to that, and see if that decodes ok.

Encrypted P25 will decode in DSD+ but it mutes the audio. Encrypted Nexedge and MotoTRBO will also decode, but the audio will come through as scrambled. The event log of DSD+ shows the channel to be Enc for TRBO, but doesn't for Nexedge.
I do agree with you, now that I have listened to other sample files that it could be Nexedge9600. I will have to pay close attention to when these transmissions happen to see which frequency that they are coming in on since they the transmissions don't occur all the time.

And another question does the frequency file have to be filled out for dsd+ to decode the audio correctly?

Thanks
 

jhampton2000

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- does the frequency file have to be filled out for dsd+ to decode

No this has just been added to help with trunk tracking. Its just a lookup file...it doesn't impact decoding.
 

jimmyjon

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- does the frequency file have to be filled out for dsd+ to decode

No this has just been added to help with trunk tracking. Its just a lookup file...it doesn't impact decoding.
Ok thanks, and you were correct about the transmission being NEXEDGE. After further digging in the frequency database I found that Emission types to be both types of NEXDEGE transmissions.

Now I just have to see if DSD+ can decode them.

Do you have any tips for getting DSD+ to decode them properly?
 

jhampton2000

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>Do you have any tips for getting DSD+ to decode them properly?

In my experience, for best results you'll have:
- Good clean signal strength
- Tune to precisely the right frequency (noting that NEXEDGE users sometimes use a + or -3.125khz offset against the freq you migth think is in use, especially NXDN4800 systems)
- A good sound card capable of 96kHz+ sampling
- for DSDPlus use the -fN function for dedicated NXDN9600 decoding, or -fn for NXDN4800

Can't help much with recommended SDR settings....I'm sure others can help here
 

slicerwizard

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jimmyjon;2****04 said:
Yes I have audio filtering checked
Well, there's your problem!

Don't use squelch or filtering on digital signals.



2****04? Where'd that come from? Is there something extra evil about 2 6 6 6 ?

Let's see: ****

Damn, there is. So does **** get turned into four asterisks everywhere? Now what would be special about ****?

2661
2662
2663
2664
2665
****
2667
2668

0666
1666
****
3666
4666
5666
6666
7666
8666
9666

So... 2 6 6 6; for when 6 6 6 just isn't evil enough.
 
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