Voice quality / Delay for APCO-25 Digital

[KAA951]

Our state just activated the first tower site of its wide-area interoperability network (800Mhz). This was my first night actually using the site and comparing it to the Motorola Type II trunked system that I normally use.

The voice quality on the digital system was poor compared to what I am used to on analog systems. Is this normal? Also, there was a delay of a second or so in re-transmission, which really messed with me when I forgot to turn my portable radio off and used my mobile radio. Is the delay part of the digital process or part of the trunked system?

 

[N_Jay]

Our state just activated the first tower site of its wide-area interoperability network (800Mhz). This was my first night actually using the site and comparing it to the Motorola Type II trunked system that I normally use.

The voice quality on the digital system was poor compared to what I am used to on analog systems. Is this normal? Also, there was a delay of a second or so in re-transmission, which really messed with me when I forgot to turn my portable radio off and used my mobile radio. Is the delay part of the digital process or part of the trunked system?

Delay comes in from both the digital radio system as well as the interoperability network and sometimes delay is added to assure there is no clipping.

 

[SCPD]

Also, there was a delay of a second or so in re-transmission, which really messed with me when I forgot to turn my portable radio off and used my mobile radio. Is the delay part of the digital process or part of the trunked system?

Both.
There is delay in the transmitting mobile. Another delay in the repeater. Yet another inside the receiving mobiles.
Using rough figures - if each step takes 300 milliseconds, you're looking at 9 tenths of a second in total delay.
-rick

 

[FuelForFire]

Both.
There is delay in the transmitting mobile. Another delay in the repeater. Yet another inside the receiving mobiles.
Using rough figures - if each step takes 300 milliseconds, you're looking at 9 tenths of a second in total delay.
-rick

That seems right on to me. Our system is has just under a one second delay. It takes a little getting used to, especially because it make the radios much more prone to feedback.

The voice quality is dependant on a number of things including firmware versions of the radios and DIU's in addition to AGC settings.

Mike

 

[car2back]

the County Jail where my agency's Comm center is located uses an APCO digital 800 repeater for their ops..... I rarely Tx on their freq, but it seems to have a minute or so delay, but I have never really noticed any feedback problems.

 

[brucewarming]

Here in WV there very near operational with the digital. In the testing stage the fire dept. had guys trying out the hand helds and they were having orientation problems with being close enough to see the other guy talking and his mouth didn't match the audio. Voice quailty also seems to fault with quick movments of the handheld. Time outs also seem to be a problem, but could be set higher in the radio. Walmarts is less than 3 miles from the local tower, you can stand at the door and see the tower on the mountian, and when inside the store, loss of signal!

 

[grem467]

the County Jail where my agency's Comm center is located uses an APCO digital 800 repeater for their ops..... I rarely Tx on their freq, but it seems to have a minute or so delay, but I have never really noticed any feedback problems.

a MINUTE delay??

every astro system ive had experience with has never had more than even a second delay,

 

[N_Jay]

a MINUTE delay??

every astro system ive had experience with has never had more than even a second delay,

Its a perception thing.

1/4 to 1/2 a second of audio delay is often perceived at "Seconds" of delay.

Never heard anyone complain of minuets before. (His life must be going by like a rocket!)

 

[Bentley]

I agree about the voice quality...(apco-25 vs. mot type II) I think the motorola type II system is MUCH clearer than the Digital transmissions. I just purchased a pro-96 today...and I am quite dissapointed with the quality of sound from apco-25 tx's. Barely understandable!

 

[grem467]

on our system its the exact opposite, the digital audio sounds worlds better than analog, but then again im using an XTS5000 with current firmware.

when i had a digital scanner on the system it did sound horrible.

the problem that keeps happening is people keep saying how bad digital is and questioning it, but dont stop to think about the differences between the radio equipments DSP/Host and a scanners DSP. It goes back to my analogy of someone hooking up a high def Dish Network receiver to a small black and white TV, then saying "why would ANYONE go with this"

 

[kikito]

the problem that keeps happening is people keep saying how bad digital is and questioning it, but dont stop to think about the differences between the radio equipments DSP/Host and a scanners DSP.

I think is highly dependent on the particular system more than anything. Our local system couldn't sound any better on any brand of digital scanner just as it does on the "real" radios. That doesn't mean other systems will be the same.

Then you have all the other factors to deal with aside from digital, operating band (VHF/UHF/700/800MHz), "modulation styles" (C4FM, LSM/Simulcast), poor implementation, etc. And then there's the interference factors that even system radios suffer from and the main drive behind rebanding, etc.

In other words, our local VHF digital system works great, that doesn't mean a similar 800MHz system in Oklahoma is going to work just as good. Regardless if you're using a "real" radio or a scanner.

 

[Bentley]

Maybe thats the problem...I'm using a pro-96 with an old version of firmware...any idea how to upgrade to the latest version?

 

[Hindscountyman]

our digital system sounds as good as talking on a landline. cant really ask for a better quality sound...

 

[bsfan1877]

Poor audio signal

here in Rhode Island, some local Fire and PD have switched to the Apco 25 800 meg trunk. I purchased 2--ye 2 Uniden 996XT---state of the art brand new scanners. I am 12 miles south of Providence in warwick. I am having much difficulty in receiving Prov Fire clearly--sometimes garbled--sometimes not bad. I purchased a spider multi band antenna which I installed in my garage rafters--with shielded coax--not much better. Is there an audio adjustment in the radio that I havent found yet to try? The manual on the CD is like an encyclopedia. I've had scanners for 30 years. This is baffling me!!!

 

[greenthumb]

Look guys, you're also comparing this on scanners, which traditionally have inferior speakers and audio filtering circuits vs. a commercial grade transceiver. And I can guarantee that even in commercial grade transceivers, audio quality can vary widely between manufacturers, and even from one manufacturer's models to another.

Using a good quality commercial transceiver that has been properly designed, P25 digital can sound every bit as good as analog FM.

 

[N9JIG]

Our local statewide P25 system has a patch on the VHF police interop channel and there is a UHF patch to that nearby as well. Traffic from the VHF side patched to the UHF repeater has a perceptible latency, and the latency of the VHF traffic patched to the statewide P25 system has a slightly longer latency.

Hear all three at the same time and it gets really freaky, the latency between VHF and UHF is about half a syllable, and the latency between VHF and P25 is over a full syllable, so you hear the voice coming at you 3 times.

When a local system started using an Astro digital system I had a system radio for a while and after getting used to it the digital audio sounded great. It did take a while to get used to it however and during the transition it was difficult to understand at times. Later, when I got a couple of digital scanners and monitored the same traffic the audio was much more difficult to understand.

That same comparison extends to our statewide P25 system, on the system radios I have heard it sounds crisp and clear, but the audio on scanners sounds clipped.

 

[slicerwizard]

hI purchased a spider multi band antenna which I installed in my garage rafters--with shielded coax--not much better.

You bought a multiband antenna to monitor a distant 800 MHz system on deaf Uniden gear? And it's mounted indoors / maybe 10 feet high? I think I see your problem. Next time go with a hot GRE receiver and a band-specific antenna and let it see the horizon.

Look guys, you're also comparing this on scanners, which traditionally have inferior

It's okay - the posters have had 3.5 years to get over it.

 

[gmclam]

P25 digital can sound every bit as good as analog FM.

LOL. Didn't they just switch from analog FM to P25?