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Old 04-21-2013, 8:27 AM
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Unhappy Vendors work to improve digital voice quality for fire communications

Two-way radio manufacturers are working diligently toward technology solutions, but for the foreseeable future a combination of best practices and training are the best way to combat the problems being encountered by firefighters when they use digital radios in very noisy environments, according to speakers at the recent International Wireless Communications Exposition in Las Vegas
Vendors say they are working on digital radio noise problems | firefighting communications - FIRE CHIEF article | Communications content from Fire Chief
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Old 04-22-2013, 8:22 AM
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The problem of background noise isn't limited to fire communications but is inherent with all digital communications. Transmit a single audio stream and digital has no problems but mix several streams together and it becomes very hard or impossible for the listener to discriminate between the signals. This is caused by the lack of redundancy with digital, analog's high redundancy furnishes the listener with the clues needed to pick out and follow a single stream from many. Digital will always have this problem as long as the bandwidth is held down to just a few kHz.

Digital radios manufacturers do not supply truly effective noise-cancelling microphones. The best way for manufactures to limit the problem with background noise is to eliminate the noise. If you don't pickup the noise then you won't have to use software to eliminate it. Get a hold of the Bose folks and hire them to design a truly effective noise cancelling mic.
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Old 04-22-2013, 11:41 AM
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Well... the issue is more mathematical than not. Two analog signals get together and heterodyne. They add together. Since our brains are the "vocoders," we can kind of pick out things, or at least recognize that two people are talking at the same time and ask one to standby and the other to say again. If one signal is stronger, a "capture effect" happens and the stronger signal covers the weaker signal completely (one of the reasons aviation sticks with AM).

In digital, there is that summing of two signals, too. What happens, though, is that a machine is attempting to reconstruct the signal and not someone's brain. Machines don't have that flexibility, unless there's an algorithm coded to do so. So, when a stream of data (and it's not purely 1's and 0's, in P25 phase I its four positions relative to zero, with each position representing a 11, 10, 01, or 00 in the bitstream) is sent, the result is destructive. The machine doesn't read it and stays muted instead. There is capture in digital, but Jack is right about that effect decreasing as bandwidth decreases. You saw this in simulcast systems, where one particular manufacture widened the P25 phase 1 signal to use less simulcast sites for capture. That doesn't fit the mask for narrowbanding, though, and some digital systems had to severely reconfigure to meet the mandate.

Digital DOES have forward error correction, and, for the 9,600 bits per second that are conveyed, about half of them are for embedded signaling and forward error correction.

There are workarounds for this limitation. 1) Training. Digital radio is not like analog, and some agencies make the mistake of assuming it is. Not stomping on other transmissions is not always common sense (especially if that's how the analog equipment has been used), it's learned. 2) Programming. You can program a digital radio to inhibit from talking over another digital signal from the same system. If the other user has an immediate emergency, they can quickly re-press their PTT button (also programmable) and talk uninhibited. But that has to be understood and set up by the vendor and system manager, and trained-on by the users.

Noise cancelling (phase cancellation, like Bose does) mics are in development for several of the manufacturers. I've heard them working and the results are better than when everyone started using digital. The question should probably be: "Why was digital ever released into production without putting it through its paces with real end-users, instead of just testing in a laboratory and then declaring great success?"
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Old 04-22-2013, 2:12 PM
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Full bandwidth digital (like 44.1KHz PCM in the red book CD mastering) sounds as good as analog.

the problem is the god awful compression.

it plain sucks.

Wanna hear worse? Today's cellphones. Horrible muffled and garbled audio, as the carriers try to squeeze every bit of voice bandwidth down to make room for data.

I'd take AMPS anyday over this compressed swirling toilet bowl. At least I can understand what someone is saying.
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Old 04-22-2013, 3:48 PM
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Originally Posted by MTS2000des View Post
Full bandwidth digital (like 44.1KHz PCM in the red book CD mastering) sounds as good as analog.

the problem is the god awful compression.

it plain sucks.

Wanna hear worse? Today's cellphones. Horrible muffled and garbled audio, as the carriers try to squeeze every bit of voice bandwidth down to make room for data.

I'd take AMPS anyday over this compressed swirling toilet bowl. At least I can understand what someone is saying.
I thought it was just me. I was an early adopter of AMPS cellular, but with digital cellphones, the extent of most of my conversation is to tell people to either call me back at my home or office. Same thing from my work-issued cellphone. I won't get one for myself. When I am forced to talk to someone, between saying, "What?" and "I can't understand you!" I am also messed up by latency where I start talking during a pause and the other guy has already started talking again. Wish I could teach these pinheads to say, "Over" and then stop talking when they've gotten their thought out (a completely separate issue about people liking to hear themselves talk...).

I have used P25 extensively, and I continue to use it. Aside from the "gollywobbles" in the sounds it doesn't know how to process, the noise issue, and one that's not mentioned frequently - wind noise, it sounds pretty good under controlled conditions. I have one radio with the AMBE vocoder but have not yet gotten to try it a noisy environment.
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Old 04-22-2013, 4:24 PM
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Quote:
Originally Posted by MTS2000des View Post
Full bandwidth digital (like 44.1KHz PCM in the red book CD mastering) sounds as good as analog.

the problem is the god awful compression.

it plain sucks.

Wanna hear worse? Today's cellphones. Horrible muffled and garbled audio, as the carriers try to squeeze every bit of voice bandwidth down to make room for data.

I'd take AMPS anyday over this compressed swirling toilet bowl. At least I can understand what someone is saying.
That's why my work still uses a motorola cellphone from 2003 it has no such thing as data on it so it only relays on voice channels. Sounds like traditional landline on it. Not no garbled talking like your under water.
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Old 04-22-2013, 5:30 PM
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Two P25 radios out there that work great in noisy environments, EF Johnson VP600 and 900. With teh design of these radios EF Johnson specifically looked at the Digital Fireground use problems.
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Old 04-22-2013, 6:40 PM
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You wanna hear BAD, Listen to P25 Phase II.. Another Forced Failure !!.. Talk about Compression
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Old 04-22-2013, 11:27 PM
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You wanna hear BAD, Listen to P25 Phase II.. Another Forced Failure !!.. Talk about Compression
Are you listening on a scanner or through an actual radio?
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Old 04-22-2013, 11:32 PM
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Two P25 radios out there that work great in noisy environments, EF Johnson VP600 and 900. With teh design of these radios EF Johnson specifically looked at the Digital Fireground use problems.
I have one of the 5100 radios with the version 6 firmware and the AMBE vocoder. Never did try it yet. Would you know if one unit alone would show improvement, or is an entire fleet needed?
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Old 04-22-2013, 11:34 PM
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Quote:
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You wanna hear BAD, Listen to P25 Phase II.. Another Forced Failure !!.. Talk about Compression
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Originally Posted by 902 View Post
Are you listening on a scanner or through an actual radio?
I'm wondering the same thing, and while I don't like to assume anything, if I had to guess I'd guess a scanner.

Our Phase II system sounds great on the APX series (6000/7000 portables, 6500/7500 mobiles, 7500 series consolettes and the MCC 7500 consoles). In fact, it sounds much better than expected, very loud and clear.


As for fireground communication...stay the hell away from digital, especially when it comes to interior ops. Analog only, I don't care what the salesmen, lab rats and tech geeks keep pushing. Maybe at some point digital will be reliable enough for fireground ops, but we're not quite there yet, especially when it comes to the current P25 and *shudders* MOTOTRBO standards.
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Old 04-23-2013, 5:36 AM
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I have one of the 5100 radios with the version 6 firmware and the AMBE vocoder. Never did try it yet. Would you know if one unit alone would show improvement, or is an entire fleet needed?
The unit being transmitted on, but this is mainly in their Next Generation VP600 and VP900(dual Band) models.
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Old 04-23-2013, 6:53 AM
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Originally Posted by Chauffeur6 View Post
I'm wondering the same thing, and while I don't like to assume anything, if I had to guess I'd guess a scanner.

Our Phase II system sounds great on the APX series (6000/7000 portables, 6500/7500 mobiles, 7500 series consolettes and the MCC 7500 consoles). In fact, it sounds much better than expected, very loud and clear.


As for fireground communication...stay the hell away from digital, especially when it comes to interior ops. Analog only, I don't care what the salesmen, lab rats and tech geeks keep pushing. Maybe at some point digital will be reliable enough for fireground ops, but we're not quite there yet, especially when it comes to the current P25 and *shudders* MOTOTRBO standards.
I agree with nothing beating analog. Unfortunately the ones who push the digital initiatives are usually the ones who came up through the ranks driving a desk. I struggle with this mindset most days, as some of these people are heavily invested and seem to have spent some of that investment money on PR people.

ETSI DMR (that turbo stuff without picking on any one manufacturer or set of "channel partners") seems to be surging in some parts of the country where there are aggressive sales. It wouldn't be "bad," per se, if several points can be addressed: 1) it dominates airtime, especially when one of the TDM slots is used for SCADA or AVL fleet management; 2) it thwarts interoperability, but remains popular probably because either the implementation costs for the interoperability standard are artificially inflated or DMR costs are artificially subsidized. Once a waveform is developed, I can't see one device, like a repeater, costing $14,000 and another costing $3,000 simply because of the waveform that passes through it. The airtime is the major issue, especially on VHF, since the channel occupancy patterns are not the same from pre-DMR to post-DMR.

And, if P25 Phase II ever breaks away from trunked infrastructure and loses the control channel so it can be a stand-alone conventional, it would "look like" DMR... but, of course, with an incompatible data protocol.

Okay, all that said, I never used DMR. Does it sound compressed?

And you guys left out iDEN. Direct Connect sounded horrible.
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Old 04-23-2013, 7:43 AM
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Been playing with DMR/TDMA for awhile now.
It's not the best and around noise it's useless.

It's very compressed and sounds like your talking out of your nose (yes newest firmware on XPR's).

The analog transmit audio is very compressed too.
Not natural sounding at all, with noise in the background it's unintelligible at times.

I think NFPA 1221 (not sure of the number) they don't recommend digital on a fireground but people still do it.

But being told to push DMR is something I will not do to public safety.
$650 for a DMR radio or $330 for an analog radio with half the size and cost.

Digital is good for somethings but has it's limitations.


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Old 04-23-2013, 7:46 AM
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DMR reminds me of iDen Direct connect.
Sounds almost the same when it loses signal too!
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Old 04-23-2013, 8:11 AM
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Working constantly with many agencies around the country, I find that the default mic gains in most radios are set way too high. When you can hear people talking in a normal voice some 5 to 10 feet away from the radios, the only conclusion is that the mic gain needs to be reduced.

You can also hear the same thing from probably 90 percent of the dispatchers. If you listen to the Boston fire department dispatchers, you can hear all sorts of things going on in the background. As many of the dispatchers like to talk some 3 to 5 feet away from the desk mics, this just adds to the problem.

Radio shops just use the factory defaults all the time and don't bother to reduce any mic gains. So put the blame back where it belongs. If the radio vendors continue to have so high of mic gain settings, then the radio systems will continue to sound like crap.

We can't fix stupid, but we can sure complain and put the pressure back on the source to fix such a simple problem. Reduce the mic gain settings. Most of the radios on the market do have the ability to turn this mic gain setting down. it just needs to be done at the time these radios are made and tested on the production line.

People need to get use to the problem of talking so far from the mic. Ever seen a police officer or a person in a fire truck leave the mic on the dash hangup clip and just reach over and key the PTT? We can't fix lazy, but we can fix the high background level most radios transmit.

Working with a radio in a real high noise environment is a whole different problem. When you add a digital radio into the mix, things go to pot very fast.
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Old 04-23-2013, 8:29 AM
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If the equipment requires more attention from the end user than push-talk-release-listen, then it should not be in the field with first responders.
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Old 04-23-2013, 9:43 AM
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If the equipment requires more attention from the end user than push-talk-release-listen, then it should not be in the field with first responders.
Agreed 100%. We should not expect first responders and LEO to be radio savvy operators like hams or even knowledgeable radio techs. First responders and LEO have too much to deal with in emergency situations without the added worry of how they are operating their radio. This is why most LMR/PS radios are very "dumbed down" when it comes to user accessible features. PTT, volume, on/off, and channel up/down is all that is needed for the end user.

What gets me is all of the small towns that are going digital, not because they need to but that's what they were sold. One small town not too far from me used to have 5 analog VHF channels. PD dispatch and private ch, tact channel, Fire dispatch, and city common. Instead of just going narrowband on their old channels, they are now on a digital trunked system with full time encryption. Total overkill.
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Old 04-23-2013, 10:10 AM
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Originally Posted by TRNcommLLC View Post
Been playing with DMR/TDMA for awhile now.
It's not the best and around noise it's useless.
Bummer John. Thank you.
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Originally Posted by jim202
You can also hear the same thing from probably 90 percent of the dispatchers. If you listen to the Boston fire department dispatchers, you can hear all sorts of things going on in the background. As many of the dispatchers like to talk some 3 to 5 feet away from the desk mics, this just adds to the problem.
Very early in my career, I worked as a paramedic in a system that used a T1600 DC remote with a paddle mic. The dispatcher would sit with the mic at hand distance, about 3 feet away from it. The room was in an old hospital with marble walls and this was before CAD, so there were punch cards and clocks. The room was an echo chamber and punching cards sounded like banging 2x4s on the desk. It's a miracle that people could hear where the calls were. Next generation of console brought a Kustom Procomm with the compression set so high that it was "ringing." The AGC made it louder in between words. Ever since then, I've been very fussy about audio. When I was running my own operation, I outlawed the desk mics. Everyone had to use headsets. People got used to them and they sounded great in the field. Subscriber equipment had to have the mic gains turned down and AGC increased by a factor of 3 (nobody can really say if that's dB, VU, arbitrary figure, whatever in CPS) for the P25 XTS/Astro Spectra radios.
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If the equipment requires more attention from the end user than push-talk-release-listen, then it should not be in the field with first responders.
Amen! Unfortunately, most agencies don't have an in-house radioman and many vendors stop optimizing a system with only very basic features and no "value added" (even if it's embedded features that have already been paid for and came ready to use in the equipment). "Oh, that's not in your spec!" Subscriber equipment especially has to be programmed to be intuitive so its users can operate it flawlessly if they are in trouble, not just programmed.
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What gets me is all of the small towns that are going digital, not because they need to but that's what they were sold.
Radio is a black box. It's even more prevalent with IT people getting tasked with maintaining a radio system. Many police officers know their weapons inside and out. They can take them apart and put them back together again in seconds. Many firefighters can calculate the pressure they need to get a certain pressure at the tip of the nozzle on the 18th floor. Many paramedics can describe the pharmacological actions of most drugs they're allowed to administer. Every one of them looks at their radio like its magic. But their radio is more likely to be the thing that saves their behind when they need help. You'd figure more people would want to learn about them and be more participants than take the ride someone is willing to take them on. Anyway, how else can a salesman meet his margin except with digital? There's nothing sexy about just reprogramming the old stuff to 11K2F3E and being done with it.
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Old 04-24-2013, 6:58 AM
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If the equipment requires more attention from the end user than push-talk-release-listen, then it should not be in the field with first responders.
Why do you think basic radio operation is beyond the ability of LEOs or First Responders? You wouldn't put a LEO in the field without some training on how to use his weapon so why are you against basic communication training? Every tool requires some training to be able to use it effectively.

That said, proper design and installation is just as important. Our county sheriff runs the dispatch center for all fire and police agencies in the county. They use a purpose-built dispatch center that is not an echo chamber yet most of their dispatches are difficult to understand due to background noise. They either don't supply or don't require the use of headset mics. Couple that with mic gains cranked up to maximum and conversations, phones ringing or the dispatcher at the next position is as loud as the dispatcher sitting in front of the mic. They all deal with the problem on a daily bases and I don't understand why they put up with it.
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