DSDPlus Explain this graph

[bobruzzo]

I am monitoring a P25 simulcast system. Using DSD Plus/Fastlane. It seems to be working ok except for some garbled audio. I took a screen shot of the GRAPH displaying while program running. I dont understand this graph. I have everything set to the freq of 853.5125 which is CC for NORTH ZONE. But why is that freq not showing up in MIDDLE of the white hi lighted area in middle of pic? I thought that would be where the main freq would be centered so you can set the bandwidth. I did try to set the correction by typing upper/lower case letter "P" to either raise or lower correction. I am not sure how to set GAIN...its about 49.6 not sure if thats too much or too little. I also have screen shot of whole screen for reference. Using rtl-sdr dongle with vertical 800 mhz antenna. Like I said everything appears to be working except for the occasional garbled audio. The NORTH site towers are all withing 5 to 8 miles from me so I am sure signal is strong enuff.

 

[air-scan]

I am monitoring a P25 simulcast system. Using DSD Plus/Fastlane. It seems to be working ok except for some garbled audio. I took a screen shot of the GRAPH displaying while program running. I dont understand this graph. I have everything set to the freq of 853.5125 which is CC for NORTH ZONE. But why is that freq not showing up in MIDDLE of the white hi lighted area in middle of pic? I thought that would be where the main freq would be centered so you can set the bandwidth. I did try to set the correction by typing upper/lower case letter "P" to either raise or lower correction. I am not sure how to set GAIN...its about 49.6 not sure if thats too much or too little. I also have screen shot of whole screen for reference. Using rtl-sdr dongle with vertical 800 mhz antenna. Like I said everything appears to be working except for the occasional garbled audio. The NORTH site towers are all withing 5 to 8 miles from me so I am sure signal is strong enuff.

In your FMP24 window there is white and green spectrographs. White is frequency. Green is the audio portion of that frequency. Frequency is displayed on the left side to have room for the audio spectrum in the middle. DSD+FL will automatically set 9.5khz bandwidth on the P25 Control Channel and switch to 12.5khz bandwidth on a voice channel. To change your gains click on the top white area of FMP24 and g/G is the keyboard shortcut for rf gain control. g is gain down shift+G is gain up. try 28 setting. P25 towers are pretty strong if your in the middle of the 25 mile radius of the entire system.

 

[bobruzzo]

In your FMP24 window there is white and green spectrographs. White is frequency. Green is the audio portion of that frequency. Frequency is displayed on the left side to have room for the audio spectrum in the middle. DSD+FL will automatically set 9.5khz bandwidth on the P25 Control Channel and switch to 12.5khz bandwidth on a voice channel. To change your gains click on the top white area of FMP24 and g/G is the keyboard shortcut for rf gain control. g is gain down shift+G is gain up. try 28 setting. P25 towers are pretty strong if your in the middle of the 25 mile radius of the entire system.

OK thanks. I set gain to 28. What other factors will produce garbled audio? I thought SDR would eliminate that, as opposed to listening on regular (sds200, bcd996p2) scanner. Some people say weak signal but the towers are not far from here. Maybe there are some other fine tuning I can do to get clearer audio?

 

[air-scan]

OK thanks. I set gain to 28. What other factors will produce garbled audio? I thought SDR would eliminate that, as opposed to listening on regular (sds200, bcd996p2) scanner. Some people say weak signal but the towers are not far from here. Maybe there are some other fine tuning I can do to get clearer audio?

In the DSD+ FL windows click on Decoder and uncheck Shaping filter. That might work. Also tweak a bit more on the ppm. FMP24 is always going to autocorrect regardless of your ppm setting.

 

[bobruzzo]

In the DSD+ FL windows click on Decoder and uncheck Shaping filter. That might work. Also tweak a bit more on the ppm. FMP24 is always going to autocorrect regardless of your ppm setting.

OK I did read somewhere to disable filters which I did...audio a little better now. I see how FMP24 DID auto correct bandwidth! How do I tweak PPM? Is PPM the setting where you adjust the offset?

 

[air-scan]

You can go into your batch file for FMP24 that you use and add the argument -a0 (a and a zero) which turns off the auto ppm correction. then save it. then reload the whole thing then you can tweak on PPM. PPM is set in .1 steps.

OK I did read somewhere to disable filters which I did...audio a little better now. I see how FMP24 DID auto correct bandwidth! How do I tweak PPM? Is PPM the setting where you adjust the offset?

 

[bobruzzo]

You can go into your batch file for FMP24 that you use and add the argument -a0 (a and a zero) which turns off the auto ppm correction. then save it. then reload the whole thing then you can tweak on PPM. PPM is set in .1 steps.

OK I got that, thanks but how do I adjust the PPM manually?

 

[air-scan]

OK I got that, thanks but how do I adjust the PPM manually?

once again p/P for ppm adjustment. p lowers ppm shift + p increases ppm same as you have done before. make sure you don't forget to click on fmp24 first to bring it into the fore window.

 

[bobruzzo]

once again p/P for ppm adjustment. p lowers ppm shift + p increases ppm same as you have done before. make sure you don't forget to click on fmp24 first to bring it into the fore window.

OK got it thank you very much!

 

[air-scan]

OK got it thank you very much!

Glad I was able to help!

If you have a equalizer of some kind that came with your computer see if there is a preset in it called treble, or treble boost. That usually also helps with muffled audio. I heard to much bass give that effect before. I also turned down my subwoofer box bass volume control all the way down.

 

[bobruzzo]

Glad I was able to help!

If you have a equalizer of some kind that came with your computer see if there is a preset in it called treble, or treble boost. That usually also helps with muffled audio. I heard to much bass give that effect before. I also turned down my subwoofer box bass volume control all the way down.

I was looking for that "enhancement" section for sound in windows. I dont think I have a "sound software" program like the kind you get when you install audio sound card. Apparently I am only using the basic Windows "high definition audio device" but not sure it is adjustable. My Brother built this PC for me so its pretty bare bones as far as sound/video. Just using the stock on-board audio/video. I do get a little more bass than desired listening to sdr.

 

[air-scan]

I was looking for that "enhancement" section for sound in windows. I dont think I have a "sound software" program like the kind you get when you install audio sound card. Apparently I am only using the basic Windows "high definition audio device" but not sure it is adjustable. My Brother built this PC for me so its pretty bare bones as far as sound/video. Just using the stock on-board audio/video. I do get a little more bass than desired listening to sdr.

SDRTrunk is less 'bassy' using a different codec library called JMBE. DSD+FL uses mp3 encoder.

See if my video is too bassy as well. This will let you know if your system is truly to bassy. I have B&O equalizer for headphone output set to treble boost.

 

[bobruzzo]

SDRTrunk is less 'bassy' using a different codec library called JMBE. DSD+FL uses mp3 encoder.

See if my video is too bassy as well. This will let you know if your system is truly to bassy. I have B&O equalizer for headphone output set to treble boost.

You have really nice audio, not overly bassy at all. How would I get and configure/use that JMBE library?

 

[air-scan]

You have really nice audio, not overly bassy at all. How would I get and configure/use that JMBE library?

Only works on SDRTrunk. I think that OP25 uses it as well.

 

[slicerwizard]

Ouch. FMP24's green display is not audio. It's the RF spectrum zoomed in around the signal you're tuned to. That's why the Z key toggles it on/off.

DSD+ doesn't use mp3 to decode digital audio. It uses the LAME encoder DLL when you tell it to create MP3 recordings.

The OP's PPM error is about 1 kHz at 850 MHz, which FMP24 seems to be compensating for. I'm not convinced that disabling FMP24's auto fine tuning and going with a fixed PPM value will help anything, especially if the dongle's drift changes due to environmental factors.

 

[boatbod]

Only works on SDRTrunk. I think that OP25 uses it as well.

LOL
You do know that op25 was able to decode xMBE audio long before SDRTrunk existed? The audio decoders (and there are two of them) in op25 were written from scratch in c/c++ by some very smart individuals. It's possible the JMBE library was derived from their work but they are most definitely not the same.

 

[air-scan]

LOL
You do know that op25 was able to decode xMBE audio long before SDRTrunk existed? The audio decoders (and there are two of them) in op25 were written from scratch in c/c++ by some very smart individuals. It's possible the JMBE library was derived from their work but they are most definitely not the same.

I didn't know the history behind it. I didn't know the two may be different.

 

[boatbod]

I didn't know the history behind it. I didn't know the two may be different.

sdrtrunk is java based
op25 is c/c++ & python based.
They both run on Linux (sdrtrunk is cross-platform) but other than that they are completely different. There are advantages and disadvantages to both, so it really depends what you want to do once you have them running. op25 makes a great streaming server but has a weak user interface. sdrtrunk has a nicer user interface but is a bit heavy on cpu usage.

 

[air-scan]

sdrtrunk is java based
op25 is c/c++ & python based.
They both run on Linux (sdrtrunk is cross-platform) but other than that they are completely different. There are advantages and disadvantages to both, so it really depends what you want to do once you have them running. op25 makes a great streaming server but has a weak user interface. sdrtrunk has a nicer user interface but is a bit heavy on cpu usage.

They both do a good job for their intended purpose. Thanks for the information.

 

[dave3825]

You can go into your batch file for FMP24 that you use and add the argument -a0 (a and a zero) which turns off the auto ppm correction. then save it. then reload the whole thing then you can tweak on PPM. PPM is set in .1 steps.

iirc, auto center tuning can be enabled/disabled while FMP24 is running: While focused in FMP24, press A to toggle auto center tuning on and off.