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| LMR digital voice codecs vs background noise http://interceptradio.com/bbs/viewtopic.php?f=20&t=9616 |
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| Author: | Hooligan [ Sat Aug 27, 2022 12:38 am ] |
| Post subject: | LMR digital voice codecs vs background noise |
An animal shelter I volunteer at is needing to replace their beat-up old radios, currently using analog-mode on some licensed UHF simplex frequencies at about a 2 acre campus. My first idea was to switch to 900MHz Spread Spectrum and save the FCC license fee, but in trying /v\ DTR-700s & DLR-1060s in the loud environment of the kennels area resulted in received poor audio intelligibility due to the vocoder not handling the combination of the desired human voice with the undesired loud barking in the near background. While that's also an issue with analog NFM, those voice transmissions are about 90% readable. I'd really like the shelter to join the 21st Century and get digital voice radios, though I'd want the radios to also have analog mode so that some other municipal analog freqs & FRS can also be programmed-in for mutual-aid/disaster interop. I'm hoping TRBO DMR does work, as some other municipal agencies are using UHF DMR simplex channels that I'd like to have programmed into the shelter radios for mutual-aid events. So now I'm starting to look at DMR flavors and will test TRBO soon, since I already have a /v\ SL300 I use at the shelter in analog mode, as well as an XPR7550e. I suppose for the heck of it, I'll test out P-25 too, though I'm not aware of any small, relatively inexpensive P-25/analog handhelds. So just wondering, does anyone have some objective (if I wanted subjective, I'd post this to RadioRetards) data on which commercial digital voice vocoder standard filters-out both sudden brief and persistent unwanted, high dynamic range (barking dogs, gunshots... et al) background audio the best? I remember years ago, the fire services had an issue with the alarm beeps from SCOTT Packs cutting-out P25 voice audio transmissions, until the P25 codec was improved. I'd love for the shelter to go with /v\ SL-300s but if the TRBO analog/digital codec doesn't perform well, I'll try NXDN flavors and maybe for the heck of it, I'll try P25. Worst-case scenario is we'll stick to analog mode, though I'd still push for analog/digital radios so that a secondary channel could be secure digital, and we'd have interoperability with some other agencies in the city that use UHF simplex DMR. |
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| Author: | Rich [ Sat Aug 27, 2022 9:32 am ] |
| Post subject: | Re: LMR digital voice codecs vs background noise |
Hooligan wrote: Worst-case scenario is we'll stick to analog mode, though I'd still push for analog/digital radios so that a secondary channel could be secure digital, and we'd have interoperability with some other agencies in the city that use UHF simplex DMR. That is actually a best-case scenario. Digital is not an upgrade, it is a downgrade. Digital sacrifices quality and intelligibility for narrower bandwidths and easier transport. |
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| Author: | nickcarr [ Fri Sep 02, 2022 11:14 am ] |
| Post subject: | Re: LMR digital voice codecs vs background noise |
NXDN9600 might be a good option but doing it cheap would be very unlikely. I think NXDN4800 might work but it's very narrow -- and that would rely upon expensive hardware for the best NR. P25 can work wonders on APX radios but even with APX1000s it wouldn't be cheap. (The APX CPS has a ton of configuration options for audio.) Phase II offers excellent noise reduction but at cost. (There is a Phase 2 P25 repeater firmware floating around that allows conventional operation -- so a trunk system wouldn't be required.) What about the DTR solution using wired headsets? What about Zello using either smartphones or the $200 android walkie talkies? Zello has software NR that might work OK. If they have a WLAN then the quality should be decent... |
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| Author: | Hooligan [ Mon Sep 19, 2022 5:36 pm ] |
| Post subject: | Re: LMR digital voice codecs vs background noise |
I tried TRBO & it actually worked well, so it's likely we'll go with analog/TRBO radios, maybe Motorola SL300s, though I'm writing the RFP to be brand-agnostic. The RFP states that for any digital vocoder besides TRBO, we'd need to have two demo radios shipped to us for testing. So I'd be happy to test NXDN if a vendor wants to loan us some. DTR won't work because DLR failed miserably, and we'd rather use RF simplex than tie-up personal smartphones/wear down our batteries, etc. using Zello or some other Push to Talk over Cellular. |
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| Author: | chpalmer [ Tue Sep 20, 2022 6:12 pm ] |
| Post subject: | Re: LMR digital voice codecs vs background noise |
Rich wrote: Hooligan wrote: Worst-case scenario is we'll stick to analog mode, t That is actually a best-case scenario. Digital is not an upgrade, it is a downgrade. Digital sacrifices quality and intelligibility for narrower bandwidths and easier transport. +1 |
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| Author: | nickcarr [ Tue Sep 20, 2022 6:26 pm ] |
| Post subject: | Re: LMR digital voice codecs vs background noise |
chpalmer wrote: Rich wrote: That is actually a best-case scenario. Digital is not an upgrade, it is a downgrade. Digital sacrifices quality and intelligibility for narrower bandwidths and easier transport. +1I would agree, but only if cost is a factor, otherwise digital is the way to go. MotoTRBO and NXDN are relatively affordable. If money is no object then go with P25 and APX hardware. Zello would be hard to beat. It would take a minimal hardware (PoC) investment and the monthly cost of operating a WLAN. Configured properly it could work quite well. |
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