DSDPlus Improving Audio Quality

[rkillins]

I am using DSDPlus FL v2.523 with two RTL-SDR dongles to monitor and track my local P25 Phase II public safety system. I think I have things essentially set up to do what it's supposed to do. I'm still learning some of the features of the app and how to utilize them to improve my understanding and experience using it on this system.

Can anyone share their experience, knowledge on how to better improve audio quality of monitored transmissions? Sometimes transmissions are choppy. Some transmissions, although legible, have a garble or wobble (not sure how to describe it). Transmissions for the most part have a higher pitch/reverb to the voice (normal for digital/). Anyway to adjust the sound quality to something a bit more "natural" less "robotic"? Perhaps I'm overlooking the purpose of some settings available to me.

We can't rule out the quality of the signal being received. Signal should be strong, but I realize that indoor telescopic antennae may not be the best to pull in digital signals.

 

[dave3825]

Its all about signal and PPM. Tune to the signal you listen to and post a screen shot of FMP24 on the voice channel.

 

[rkillins]

Thank you @dave3825. I appreciate your reply. Here's a pic of FMP24 signal on a P25 II voice transmission. Anything in your opinion from it that can help determine whether my audio can be improved, be more reliable?

 

[PDXh0b0]

Two dongles so you are running fmp24-CC.bat / CC.bat & fmp24-Vc.bat / VC.bat?

If so, open your fmp24-vc.bat with a text editor, add -b-12.5

Save as FMP24-VC(p25).BAT

Run fmp24-cc.bat , cc.bat, fmp24-vc(p25).bat, vc.bat

 

[rkillins]

Hi @PDXh0b0 ... yes two RTL-SDRs and running all 4 .bats. Everything is decoding and tracking properly, just crappy audio. Very muffled sounding today. Maybe to be expected and my expectations are too high. Not sure what to expect in comparison to audio on my SDS100.

My FMP-CC file contents:

FMP24 -rc -i3 -o20001 -b12.5 -g20.7 -P-1.6 -f866.9750

My FMP-VC file contents:

FMP24 -rv -i2 -o20002 -P-1.6 -g20.7 -b12.5

add -b-12.5

Are you recommending I change these to -12.5? vs the current -b12.5?

 

[PDXh0b0]

Hi @PDXh0b0 ... yes two RTL-SDRs and running all 4 .bats. Everything is decoding and tracking properly, just crappy audio. Very muffled sounding today. Maybe to be expected and my expectations are too high. Not sure what to expect in comparison to audio on my SDS100.

My FMP-CC file contents:

FMP24 -rc -i3 -o20001 -b12.5 -g20.7 -P-1.6 -f866.9750

My FMP-VC file contents:

FMP24 -rv -i2 -o20002 -P-1.6 -g20.7 -b12.5

Are you recommending I change these to -12.5? vs the current -b12.5?

Just the fmp24-vc.bat it will lock it too 12.5 instead of the 9.5 it normally uses. See if it sounds better for you

 

[dave3825]

Are you recommending I change these to -12.5? vs the current -b12.5?

If so, open your fmp24-vc.bat with a text editor, add -b-12.5

He is saying change to -b-12.5 (minus b minus 12.5 with no spaces)

FMP24 2.19 says:

Some scanner mode bugs have been fixed

-b-<bw> bandwidth locking command line option added

Example: -b-12.5

When this option is used, FMP24 ignores bandwidth hints from DSD+;
use this option to manually control bandwidth in -rc and -rv modes

Your using 2 dongles so one stays parked on the control channel and tells the other dongle where to tune for a voice call. The -b-12.5 will keep that dongle at 12.5 which might be going to 9.5 on voice call.

 

[dave3825]

And to add, your gain is set the same on both dongles. I have a few systems where voice channels are received at different levels than the control channel, and voice channels themselves are received at different levels.

I am out on Long Island. I can receive a trunked systems control from NYC enough for it to decode and show all activity. . When it switches to some voice channels, some of them are much weaker than the cc. Some produce voice and most others do not. They normally would be putting out the same wattage but since I am far away, some get degraded differently by the time they get to me.


What you also can try is play with the gain in the voice fmp24. Bump it up to where the signal peak reaches its highest point, and to just where the noise floor starts to rise.

 

[rkillins]

Thank you both for your support. I didn't know you could have a negative bandwith value. I've made that change as suggested, as well as experimenting with the VC gain value. I feel there may be some improvement to the quality, time will tell.

 

[dave3825]

I didn't know you could have a negative bandwith value.

While it looks like that, its not a negative value. It forces 12.5 to stay and not switch to something else. Different modulations use different bandwidth.

This is listed in FMP24.scanlist. With out inserting the - as you did, the tuner (FMPx) will change based on the modulation being detected in DSDPlus. So without the minus, when these are detected, it will switch to them.


.

 

[rkillins]

Ah, ok. That was helpful. Thank you.

 

[mtindor]

Depends upon what you mean by audio quality. Audio quality in DSDPlus is not quite as good as in SDRTrunk. Your signals look fine. 9.5 BW setting is fine for P25. Hell, I'm using SDRSHarp and an spyserver in South America to monitor a huge trunked system down there. I don't use SDRSharp plugins, but I did, they want to use 9.37 khz for the bandwidth. So that's what I have SDRSharp set to. Everything works gloriously. It's not like widening te bandwidth to 12.5 khz is going to make any difference in audio quality. At least that's my belief.

 

[PDXh0b0]

Depends upon what you mean by audio quality. Audio quality in DSDPlus is not quite as good as in SDRTrunk. Your signals look fine. 9.5 BW setting is fine for P25. Hell, I'm using SDRSHarp and an spyserver in South America to monitor a huge trunked system down there. I don't use SDRSharp plugins, but I did, they want to use 9.37 khz for the bandwidth. So that's what I have SDRSharp set to. Everything works gloriously. It's not like widening te bandwidth to 12.5 khz is going to make any difference in audio quality. At least that's my belief.

🤷🏼 it sound better to my deafening ears, but then 172 khz sounds better to me than 20p khz with broadcast fm

 

[mtindor]

🤷🏼 it sound better to my deafening ears, but then 172 khz sounds better to me than 20p khz with broadcast fm

We are talking digital signals here. The correlation just isn’t there when it comes to your ears or my ears and digital

Increasing your filter BW on the digital signal, pre-processed, is never ever going to be heard by your ears once the decoded audio is presented to you. If the digital signal is showing no errors in the decoding program at 9.5 kHz, then that is where it belongs

Try something like monitoring an IDAS or Nexedge48 signal at a 12.5 or 20 kHz bandwidth versus the suggested 4 kilohertz bandwidth you will see quite often that it is more difficult to decode because there’s so much noise included with the signal

Mike

 

[ultrajv]

You probably have a high noise floor due to indoor antennas Best to use outdoor antennas. Looking at your signal, its not strong enough.

 

[Benkasey]

The muffled quality you hear is because the digital systems like P25 use highly compressed bandwidth. It's like how the old POTS telephones sounded vs. HD Audio (like AM mono vs. FM). I haven't heard these transmissions on a commercial radio like the responders use, but it's probably better using their signal processors and codecs.

I find that the sound quality of SDR Trunk is somewhat better than DSD+. I have thought about ways to pipe the audio through a graphic equalizer to add more treble. Might be fun to experiment with AI to see what it could do.