SDRTrunk P25 Sound Quality

[scottct1]

My local police and fire will be moving to Digital P25 early next year. I am the person who puts their scanner feed online here.

I have been working with the police department on this switchover and they put up a simulcast of our fire department from the analog to the new P25 system for me to test thins out and make sure I can pickup and rebroadcast them when they move over.

I have setup a computer with SDRtrunk and can pick the test feed up. My antenna seems to be ok, I am gettin a power level of around -20.0 with a peak of -11.5. (As shown in SDRtrunks Channel / Power screen.

I have 3 SDR dongles hooked up and all appear to be working.

The issue is the sound quality. I am new to listening to digital scanners but to me the sound quality is hard to understand.

Here is a sample... audiotest.mp3

Is this the way that things are supposed to sound using SDRtrunk?

I don't really want to spend $700 on a SDS-200 but will if there is a dramatic increase of sound clarity one one.

Is digital radio supposed to sound like this? is it a SDRtrunk issue, is it just the way P25 is supposed to sound, or shall I bite the bullet and buy a SDS200? I wanted to use SDRtrunk to not only send audio to Broadcastify, but also wanted to add the feed to their feeds service as well.

Thanks for any advice you can give.

 

[RaleighGuy]

@scottct1 have you tried other decoders? I use Unitrunker V2 and Trunking Recorder to feed to Broadcastify and it seems to be doing good for years now.

You might try others and see how they sound before deciding to make the jump to a SDS200.

 

[ChrisABQ]

We have cities still in the process of switching over to full P25 system, but before they do, they are "patching" the older system to the P25 system. This exactly what the patched calls sound like as they are not native to the system. Once they move over to the system, the audio will be much better. SDRTrunk is the easiest and best sounding software to use.

 

[wgbecks]

I have been working with the police department on this switchover and they put up a simulcast of our fire department from the analog to the new P25 system for me to test thins out and make sure I can pickup and rebroadcast them when they move over.
---
The issue is the sound quality. I am new to listening to digital scanners but to me the sound quality is hard to understand.

How does the fire departments audio sound when listening to them direct? I am a regular user of OP25, SDRTrunk and a few other applications and don't think the mushy audio is due to the software application.

On the surface, it sounds to me like the audio level from the analog system is hitting whatever device that its tied to at the console a
bit too hard and is exceeding the encoding capability of the IMBE encoder on the P25 side.

Perhaps you might speak with the systems radio technician as ask if the analog audio feeding the patch can be lowered somewhat
to clean up the digital compression that seems to be taking place?

For a comparison, I am attaching a short audio clip recorded with OP25 from one of my feeds.

 

[scottct1]

FD Audio sounds fine on the analog feed.

BTW I should add this is a P25 Phase 2 system.

I added a neighboring town which is is on the same system and most of what I am hearing I can't tell what they are saying.

 

[dave3825]

BTW I should add this is a P25 Phase 2 system

Thats rules out Unitrunker

My antenna seems to be ok, I am gettin a power level of around -20.0 with a peak of -11.5. (As shown in SDRtrunks Channel / Power screen.

You might be overloading. Can you post screenshots of the spectrum and the settings in the tuners tab? Like whats posted below?

The issue is the sound quality.

How is the PPM looking in the tuners tab on each dongle?

 

[Project25_MASTR]

Given the MDC data burst at the beginning of the sampled audio, it's clearly analog patched audio over to P25. Depending on how this patch is set up and the audio sources for the two systems, this can have some wonky results. Best way to tell is to wait and see for P25 subs to get onto the system and listen to how native P25 (i.e. not analog patched to P25) audio sounds.

 

[scottct1]

Thats rules out Unitrunker


You might be overloading. Can you post screenshots of the spectrum and the settings in the tuners tab? Like whats posted below?



How is the PPM looking in the tuners tab on each dongle?



View attachment 152763

Tuner one is showing -0.05

Tuner two is showing -2.063


I have placed a test feed online to one of my own servers. http://music.satelliteguys.us/SCANNER

In this feed I have the test feed, but also added a live feed to another town that is also using the same system and has been on that system for years.
Who knows, maybe this is what Digital is supposed to sound like and I am not use to it. But if I can do anything to make it sound better I am all for it. I would rather now spend $700 for a SDS200 but if it provides the best sound quality then I am all for it.

Thanks for the advice and help!

 

[dave3825]

I am gettin a power level of around -20.0 with a peak of -11.5. (As shown in SDRtrunks Channel / Power screen.

Can you post a screenshot of the that tuners gain settings with that tunes spectrum showing?

Tuner one is showing -0.05

Tuner two is showing -2.063

once you get them as close to zero, try uncheck the auto adjust.

 

[Ubbe]

When one of my biggest customers where transition from analog trunked to digital I had to use a patch module that Motorola supplied to me, I believe there was 8 or 12 of them and each one connect to a TG at both sides. The immediate problem where the audio quality. I could choose to use automatic gain control or not but without it there was too much variations in the audio level that the digital system didn't like. Digital are much more sensitive to audio levels. But the AGC compressed the audio too much and will then strip off the highest frequencies making it sound muddy and mushy and difficult to understand, much like the audio in that P25 sample. In a $100 home studio audio compressor it adds a high frequency EQ boost to compensate when it compress the sound but this radio systems patch module AGC didn't had that basic function.

I had to modify that patch and insert capacitors in series with their inputs to get rid of the powerful low frequencies and at the same time it lowered the general audio levels into the AGC circuit to reduce the compression level. It gave a huge improvement in sound quality, almost impossible to tell if it was a patch from the other system or a call locally within the system.

How the audio ends up being heard are up the the engineers who proactively listen to the system and adjusts levels and make modifications if something isn't working to their satisfaction. If the patch only are going to be in use for a week or two then the engineers might just install it according to instructions and be done with it. But for a year long patch or permanent it will be important that it holds the highest possible quality both in audio and functionality.

/Ubbe

 

[scottct1]

The patch is temporary for the next few weeks. They are having issues with their new radios and are waiting for a firmware update. So they are looking at sometime in Q1 of 2024. I just want to be ready for them.

The patch is just for testing no PD or Fire member has a new radio yet which can access it. Its basically me and the radio techs so far who are accessing it.

I moved the antenna outside this weekend and it seems to have helped a bit, I don't seem to be missing, many (any) calls like I was earlier.

As I mentioned above I added the fire department from the town next tewn over which is using the same digital system / setup (same system just different talkgroups) and I put up an Icecast server as a test which you can hear at http://music.satelliteguys.us/SCANNER

 

[PPRCN1]

As others have mentioned, if it's patched, all bets are off. Can you get a hold of a radio and do some audio testing on a test TG? I have had SDR-Trunk running for several years now on a Phase I P25 system, and the audio is just fine. I actually host the system at one of the simulcast RF sites - with no antenna connected to the SDRSPY radio. Also, make sure your decoder is set to LSM rather than C4FM if it's truly simulcast.

All that said, Phase I audio sounds closer to FM to my ears than Phase II.