Digital vs Analog

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KC0KM

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I have question, about digital vs analog transmissions. I have noticed this not only on my scanners, but also with digital vs analog television as well. However, in this case I will use the scanners as the example. I have three primary scanners, one is a Radio Shack Pro-106, (a digital trunk tracking 3), second is a Pro-2051 (an analog triple trunking 3), and the third is a Bearcat 245XLT, (a HT trunk tracker 2). I scan the KCMO (digital) system on the 106, but I have also analog in it as well. One of these is MERS (Metropolitan Emergency Radio Service), which is primarily used by the local NWS/NOA office to give out weather reports to the are fire departments. They send out a "report" every morning, and sometimes (when I am awake) I am able to hear it. This is the problem/question. If I have the two analog radios on, they will be in synch, however, the digital radio is a few seconds (if not fractions there of) behind. The result is an echo or reverb effect. I have also noticed this on the flat screen (digital) TV, and the old analog TV as well, even though both are off the same feed, the analog is ahead of the digital audio.

My question is why? I simply do not know why or understand why the audio signals do not match up and are not in synch. Any ideas?

73 KC0KM
 

Ed_Seedhouse

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I have question, about digital vs analog transmissions. I have noticed this not only on my scanners, but also with digital vs analog television as well. However, in this case I will use the scanners as the example. I have three primary scanners, one is a Radio Shack Pro-106, (a digital trunk tracking 3), second is a Pro-2051 (an analog triple trunking 3), and the third is a Bearcat 245XLT, (a HT trunk tracker 2). I scan the KCMO (digital) system on the 106, but I have also analog in it as well. One of these is MERS (Metropolitan Emergency Radio Service), which is primarily used by the local NWS/NOA office to give out weather reports to the are fire departments. They send out a "report" every morning, and sometimes (when I am awake) I am able to hear it. This is the problem/question. If I have the two analog radios on, they will be in synch, however, the digital radio is a few seconds (if not fractions there of) behind. The result is an echo or reverb effect. I have also noticed this on the flat screen (digital) TV, and the old analog TV as well, even though both are off the same feed, the analog is ahead of the digital audio.

My question is why? I simply do not know why or understand why the audio signals do not match up and are not in synch. Any ideas?
Digital broadcasts have to be sampled and digitized, then converted back to analog at the receiver. This takes a bit of time.
 

marksmith

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I have a 996xt and a 536hp. I get the delay you describe when both are monitoring the same digital broadcast but not when they are monitoring a non-digital transmission. So I have determined that it is the digital decoding process of the radios that are different in my case.
 

scanchs

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I have a 996xt and a 536hp. I get the delay you describe when both are monitoring the same digital broadcast but not when they are monitoring a non-digital transmission. So I have determined that it is the digital decoding process of the radios that are different in my case.
+1

I have noticed the same echo/reverb effect between the HomePatrol-1 and the BCDx36HP series when they are receiving certain digital signals. They all play in unison when the signal is analog. I came to the same conclusion, that the digital decoding process is different enough between the HP-1 and the x36HP series scanners to create a slight delay that results in an echo/reverb effect when listening to them all together. The 436HP and 536HP play in unison, while the HP-1 creates an echo/reverb effect with either or both of the x36HP scanners.

ScanCHS
 

commscanaus

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This delay or echo as it is experienced is known as latency.
It is essentially the time taken to decode the digital bitstream and output the resulting audio.
Since this requires fairly precise timing in the decoding phase, two or more receivers will usually create the echo when receiving the same signal since their internal clocks will not be sychronised.

There is an inherent amount of latency with digital due the time taken to encode and decode the information, whether it be speech, video or whatever.

Listen to a digital radio broadcast at a game and see a touchdown scored and wait a couple of seconds for the announcer to call the play. Analog is definetly better for up to the second events!

Commscanaus
 
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