P25 audio quality

[fmalloy]

In many places the audio was pristine on the mobile radio, but was horribly garbled on the scanner.

Good to know, thanks.

So with digital seems the whole playing field changes. With analog, I guess it's much more straightforward to design a radio receiver, and trunking was as complicated as it got. With multicast, it challenges the already complex DSP, decoding, and error detection/correction a radio has to do.

Still, your cell phone is a digital radio, and the sound quality (relatively speaking) and signal reliability are there, and doesn't require "professional equipment" costing thousands. How does it manage to handle signals that come from multiple towers? Seems to handle it a lot better, wouldn't you say?

Some links for thought:

Simulcast, multicast or hybrid Solutions | P25 Best Practice

Perceived shortcomings of P25 | P25 Best Practice

 

[ofd8001]

Still, your cell phone is a digital radio, and the sound quality (relatively speaking) and signal reliability are there, and doesn't require "professional equipment" costing thousands. How does it manage to handle signals that come from multiple towers? Seems to handle it a lot better, wouldn't you say?http://www.p25bestpractice.com/specifying/perceived-shortcomings-of-p25/

Just guessing, I'd say a cell phone is more "pointed" in what it supposed to do, versus the "broad brush" of a scanner.

Plus when you build, probably, millions of something versus hundreds/thousands, the cost of doing so drops dramatically.

The articles you referenced are interesting and for whatever its worth, they make good sense to me.

It was definitely a wierd thing to experience when you could be standing next to someone with a digital radio and listening to them saying something, but it didn't come over your radio until a couple of milli-seconds later. That's the delay in digitally processing the voice.

 

[fmalloy]

It was definitely a wierd thing to experience when you could be standing next to someone with a digital radio and listening to them saying something, but it didn't come over your radio until a couple of milli-seconds later. That's the delay in digitally processing the voice.

Yep. The voice has to be sampled and filtered/compressed/encoded/digitized for transmission. Error correction codes have to be calculated and added. Everything has to be packetized and processed, and modulated over the signal. Then the receiver has to detect this data, decode it, process it, and apply the error correction for all the bits that got lost/mangled over the airwaves, and then do digital-to-analog conversion and try to somehow reconstruct the audio with some level of fidelity.

Digital audio can provide fantastic quality when storing audio on medium like CDs, tape, and silicon memory. It's also great when you have a strong, single source signal like a satellite. For simulcast local public service radio with moving mobile units, not so much.

Wondering what was so broke with analog that this whole mess had to happen.

For some things, simpler is better.

 

[kayn1n32008]

Good to know, thanks.



So with digital seems the whole playing field changes. With analog, I guess it's much more straightforward to design a radio receiver, and trunking was as complicated as it got.

Trunking does not complicate it per-se, trunking just dynamically assigns channels out of a pool of available frequencies. It allows for a more efficient use of limited resources. With analogue trunking, you are still just listening to analogue transmissions. Even analogue simulcast systems(trunking or conventional) will sound ok, as long as you are with in the engineered coverage area.

With multicast, it challenges the already complex DSP, decoding, and error detection/correction a radio has to do.

I believe you are referring to simulcast, the difficulty scanners have with LSM(Motorola simulcast) is that rather than use C4FM modulation, like a conventional, or multicast trunk system uses, LSM uses CQPSK instead. To properly decode CQPSK you need a receiver that output I&Q data, rather than using a discriminator tap that is just fine for C4FM, heck you can even decode DMR, NXDN and even Provoice formats using a simple discriminator tapped scanner. CQPSK a is a different modulation, and a different wave form, and does not decode very well using a discriminator tapped receiver.

Still, your cell phone is a digital radio, and the sound quality (relatively speaking)

And uses a channel MUCH wider than a LMR voice channel.

and signal reliability are there,

Because it is in the telco providers best interests to provide the coverage their consumers demand. Where as first responders get that ever the politicians decide to fund... While we all want the Cadillac system, that gives 100% portable on belt, interior of building coverage 100% of the time, the reality is that most governments cannot afford to provide it. So usually they buy the 95% mobile, primary highway coverage 95% of the time Volkswagen Beetle system. They then blame the lack of portable on belt coverage on the vendor, and end up, in the end, paying for the 'extra' infrastructure to give them the coverage they actually wanted in the first place.

and doesn't require "professional equipment" costing thousands.

But your phone is not designed to take the beating that a public safety user will impart on their LMR equipment.

How does it manage to handle signals that come from multiple towers?

It doesn't, it listens to one sector of a cell site at a time. And when certain criteria are met, the call will be handed off to the adjacent site.

Seems to handle it a lot better, wouldn't you say?

See above

Some links for thought:

Now that I replied to this post, I will take some time to read the documents you linked to.

Do realize that you can NOT compare public safety LMR to that cell phone you are carrying in your pocket. To completely different technologies, for different missions, funded in completely different ways.


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[fmalloy]

While we all want the Cadillac system, that gives 100% portable on belt, interior of building coverage 100% of the time, the reality is that most governments cannot afford to provide it

Cost is always a major factor, which brings us to my original question - what exactly are the benefits of P25 to public safety, then?

It's not cost, it's not simplicity...what is it?

 

[kayn1n32008]

Cost is always a major factor,

Yes it is. Too bad it is politicized, and sadly it is our first responders that suffer as a result.

which brings us to my original question - what exactly are the benefits of P25 to public safety, then?

I'm not sure I can actually quantify that.

Uniform audio with the coverage area. Clean audio with the coverage area no static. Having everybody on one band. When dealing with incidents that require resources from a wide area, when you are all using the same system, you do not need to have radio caches. This also reduces the overlapping infrastructure.

While the city I live in uses EDACS, the same thing applies. We have all city services using the same network. For a city of 1million people our network uses 20RF pairs, if each talkgroup required 1 repeater pair we would need, probably, 2-300 repeaters. Trunk systems are much more efficient users of already scarce RF spectrum.

I personally prefer digital radio to analogue, I like not having to constantly having to change volume levels with varying signal strengths. I also do not miss the static, and hiss of weaker signals. While I do not use P25, I do use DMR in an industrial setting, where the system owner has properly engineered, and just as importantly properly funded, their system. The system was installed by competent technicians, that have tuned the system to function best. All subscribers are using current firmware, and have AGC properly set up. While it is a UHF a system, it has superior coverage to the VHF system it replaces.

I think the biggest issue with noise cancelling technology/AGC/DSP, is user education, in how to use the technology, how to properly talk into the mic/radio to maximize the technology inside.


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[jim202]

One thing you have to remember about trying to compare a cellular conversation to a public safety digital conversation is what type of a system the public safety system is using and how far away the tower is. In the cellular system the tower your using is probably no more than 3 or 4 miles away unless your out in the country. The cellular system is using a dedicated channel that is not re-used until you get 2 towers away.

The public safety system is probably running a simulcast system. This means you have maybe 3 or 4 towers that could be heard at the same time in some locations, all using the same channel. More likely just 2 or 3 towers. Anyway, the digital data stream in a simulcast system is designed to provide coverage in the overlap area between multiple sites. The timing of the data stream from each of the towers is critical. It takes a good receiver to decode the data when you get into the overlap area. The choice of which vocoder being used in the receiver, adds to part of the reception problems that you hear people complaining about.

The best you can do in a simulcast system is to try to limit the reception of multiple towers. In a base setup, this is easy to do with directional antennas. However out in the field in a vehicle or hand held use, your SOL in trying to limit the problems. Best you can do is move a couple of feet and try to find a hot spot for one of the towers.

Will better vocoders solve the problem? Maybe, but don't expect to see it happen in any scanner in the near future. It would mean the vendor would actually have to do some research to find the better choice of what is on the market. Plus it would cost a little more. In looking at it from the vendors side of the picture, it probably never happen. The scanners cost way too much now. Adding more to the cost of the scanner will only turn the customer away from buying it.

 

[ofd8001]

Will better vocoders solve the problem? Maybe, but don't expect to see it happen in any scanner in the near future.

I believe the x36 scanners and the HP2 are using different vocoding technology.

My 536's are much better at decoding our local P25 simulcast system than my x96 scanners.

 

[fmalloy]

Will better vocoders solve the problem? Maybe, but don't expect to see it happen in any scanner in the near future. It would mean the vendor would actually have to do some research to find the better choice of what is on the market. Plus it would cost a little more. In looking at it from the vendors side of the picture, it probably never happen. The scanners cost way too much now. Adding more to the cost of the scanner will only turn the customer away from buying it.

Sad, really sad.

The hobby is about radio and listening to your local Public Service agencies and keeping connected to what's going on.

Now, we have to worry about CQPSK and digital coders and simulcast and ultra-directional antennas and interference and P25 settings.

The dispatcher and unit sound like two 90's voice synthesizers talking to each other. Yeah, no noise, no static. The real life drama and emotion is pretty much gone and filtered out, digitally. Well, I guess that's great if you're a LEO and those $3,000 Motorola radios work well for you. That is what it's all about anyway.

I suppose everything is going to be encrypted eventually, and the whole hobby is going to die out anyway as a result.

Sorry to sound so negative, but this is the reality.

 

[ratboy]

I just want just once for someone that says P25 sounds so great to cough up some evidence of that. Upload a file .. but I think we all know that can be faked, so that is not even definitive proof.

From my experiences P25 sounds like crap compared to analog. I think it is cause they are just used to it .. but to someone that is new to it and has an open mind .. tells it as it is, it sucks.

I spoke to one of my friends a long time repeater technician .. his words much like my thoughts "any digital format is going to sound like **** compared to analog". I agree .. I have yet to see any proof otherwise.

Hey, there are people who think the Sirius/XM radio in their cars sounds good, too. It doesn't. It sounds pretty bad, at best, and sometimes, just awful. Digital voice can sound ok, at best, but most of the time, it sounds pretty bad. Analog almost always sounds a lot better.

 

[fmalloy]

Hey, there are people who think the Sirius/XM radio in their cars sounds good, too. It doesn't. It sounds pretty bad, at best, and sometimes, just awful. Digital voice can sound ok, at best, but most of the time, it sounds pretty bad. Analog almost always sounds a lot better.

Digital can sound good, very good. But, you need a reliable transmission medium with a large enough bandwidth so that the sampling and error correction are sufficient and you don't drop too many bits due to weather, terrain, etc.

The problem is, Public Service radio is lousy - low power, unreliable, simulcast issues, bandwidth cut down to a minimum, TDMA...

Sirius is satellite, so a good signal comes beaming down from above blanketing the entire country. You don't get that with public service towers and the error rate is crazy. So the audio sounds like Stephen Hawking's synthesizer or Daft Punk's vocoder.

for Public Service, analog works. You get some static, some noise, but its intelligible. Your brain can still hear the details. And to be honest, marginal analog signals have much more audio detail than a strong digital simulcast signal, where you've got digital bits coming from all directions and it can't be sorted out.

To summarize: digital audio is extremely high fidelity - when the medium is consistent and reliable and of high bandwidth. It's not meant for weak, vulnerable simulcast signals.

 

[kayn1n32008]

Sad, really sad.

What is sad is that Uniden decided to use an inferior method to get data to the decoder. They did this knowing that CQPSK a is starting to be widely used.

The hobby is about radio and listening to your local Public Service agencies and keeping connected to what's going on.

Sure is, and as such the network owners are going to implement the technology that makes sense, not the technology that works best for scanner users.

Now, we have to worry about CQPSK and digital coders and simulcast and ultra-directional antennas and interference and P25 settings.

I guess, what would make sense is if the scanner manufacturers would design a receiver to properly receive and decode CQPSK. Blame the scanner manufacturers.

The dispatcher and unit sound like two 90's voice synthesizers talking to each other.

I guess. But remember you are listening with an inferior receiver. Designed to to much more than listen to a single mode, and band.

Yeah, no noise, no static.

Sure is, and with modern noise cancelling technology, a lot nicer to listen to. Voices are easier to understand when all that other crap is gone.

The real life drama and emotion is pretty much gone and filtered out, digitally.

It makes users easier to understand.

Well, I guess that's great if you're a LEO and those $3,000 Motorola radios work well for you. That is what it's all about anyway.

Bingo. That IS what it is all about. It's about the users, and thier ability to clearly communicate. Not how a system sounds to a scanner listener.

I suppose everything is going to be encrypted eventually, and the whole hobby is going to die out anyway as a result.

Likely. And it is a different topic, that I will not comment on here.



Sorry to sound so negative, but this is the reality.[/QUOTE]





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[fmalloy]

Well, today I heard what P25 is supposed to sound like.

First, I put the famed RS 800MHz antenna, which I just got yesterday, on the 436. This improved the P25 signal reception and the number of calls received, and also improved reception of analog systems (150/460MHz, etc.) across the board. And, it's shorter than my previous antenna. However, the P25 audio, which came through more often, was still very garbled and choppy.Unintelligible, really.

Took the scanner into work, which is about 7 miles away and the result was quite different. Even though I'm deep in an office building with lots of metal girders where even cell reception is bad, I'm able to receive my local city and neighboring city's P25 phase II clearly. There's still a bit of that digital vocoder/robot sound, but at least it's clear and understandable, with no breakups or distortion with those short pops/clicks I get at home, which is guess are indications of uncorrectable errors and dropped data.

When i get back home will walk the neighborhood with the RS 800 and see what happens.

Ironic it sounds great at work, but not at home where I want to listen.

I guess I'm one of those "lucky" folks whose listening location has simulcast issues, with delayed digital data from multiple sources confusing the scanner. I like to take the scanner to multiple rooms in the house and am not real excited to mount a directional antenna outside and drill holes to run antenna cable. The wife wouldn't be too happy about that.

 

[sparklehorse]

I like to take the scanner to multiple rooms in the house and am not real excited to mount a directional antenna outside and drill holes to run antenna cable. The wife wouldn't be too happy about that.

In most houses the easiest place to bring coax in is to drill a hole through the bottom rail of a window. You'll only have a couple inches of wood to get through, and nothing else. Be sure to drill well clear of of the glass, and be sure you drill a large enough diameter hole to accommodate the BNC or other connector on the end of your coax. Drill at an upward angle from the outside so rain won't come in, and put a drip loop in the coax right before it enters the house. If you sell the house down the road it's an easy hole to fill in. The wife will be happy you're home enjoying your hobby.


G

 

[hemi]

My 436 is giving me fits on Motorola type 2 p25, audio cuts in and out, miss most of the conversations

 

[TxScanner]

I tried a 436 and hp1, both of which did ad you explained

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[cpetraglia]

P25 Reception

Here is the approach I took. I too am in the middle of a six tower P25 system in my own city of residence and got terrible reception at first with one scanner. This can get expensive. I now have a Yagi antenna out doors fed into a PSR800, PSR600 and a 996XT. All set on the same talk group going through a small mixer and to an exterior amp and speakers. All three radios behave differently listing to the same transmission. But with all three added toghether, I can listen comfortably. The only way you'll get great reception with a portable antenna is to get very close to one tower. I have a PSR 600 in my vehicle with an 800MHZ roof mount antenna. In my driveway I get crap. Drive south 3 miles and it sounds crystal clear all the time. The garbled problems are a direct result of simulcast distortion.

 

[MrAntiDigital]

With all the extra expense, the distorted signals, the limited reception, it's just not worth it anymore. They can go to P25, P225 or P325, I am finished with the hobby. It's just not worth the grief, or the expense to continue.

So I am not spending one more cent on any digital scanner of Phase 1 or Phase 2 or whatever else kind of pipe dream invention somebody comes up with.

I watched my brother spend hundreds of dollars, buy special coaxial cable, special antenna and he can't pick up a small city about 15 miles from his house that he used to hear loud and clear on UHF. And all he had to do was put in about 6 numbers on his scanner and it worked fine.

Now that same place has gone digital. He has spent hundreds of dollars trying to pick up just that one channel. But now he is very sorry he did it. For those who want to gamble with their money, go to a casino, you'll probably do better there.

For those PRO digital users who are happy with their systems, great. I'm just reporting it as I see it.

 

[MTS2000des]

The garbled problems are a direct result of simulcast distortion.

There is "simulcast distortion".

The problems are a direct result of these turdy scanners that aren't designed with the proper circuit needed to demodulate what you are trying to receive.

A radio with the right stuff would sound great, and you wouldn't need a Rube Goldberg arrangement of 3 scanners tuned to the same frequency/talkgroup.

Consumer digital scanners are garbage pail junk. That is the root problem.

 

[MONITORING247]

p25 systems clarity and in general

i agree a professional 2-way will always take it over a scanner from filtering to sensitivity in the 700/800 systems 0.8 mv is considered good p25 receive the p25 motorola units are down to 0.2 mv to receive the same system as you all know many are now making a yagi beam to help there scanners bring in clear p25 simulcast also the coax in the fire and police units are made for the least amount of signal loss and the mobile antenna are designed for p25 systems only... take into account all these factors and the scanner be it uniden, realistic, gre, whistler aor, are mere "toys" in the realm of professional safety radio. HAPPY SCANNING NOTE: we also need to take into account the distance of a p25 signal EXAMPLE : WHEN I WAS IN CHICAGO the p25 system was crystal clear as i drove out of chicago and got home the same system was garbled and unreadable this also must be taken into account.