[op25-dev] Why can't I hear fire tones?

'William Becks' wllmbecks@gmail.com [op25-dev] op25-dev at yahoogroups.com
Sat Jun 16 23:33:19 UTC 2018

It’s obvious that the software vocoder in OP25 does not decode all/some tones as does the DVSI hardware solution used commercially.

For your information, the simulcast question was to query why his scanner was having difficulty with missing transmission as virtually all consumer grade scanner receivers have great difficulty with simulcast systems.     If you’ve been following the thread, the users wants/desires the tones that are not being decoded/reproduced by OP25.   That is why he needs to seek another solution.   Maybe you have the skills to rewrite the vocoder code for o25.  That would be nice!





From: op25-dev at yahoogroups.com [mailto:op25-dev at yahoogroups.com] 
Sent: Saturday, June 16, 2018 5:20 PM
To: op25-dev at yahoogroups.com
Subject: RE: [op25-dev] Re: Why can't I hear fire tones?



I don't see how anything in your replies is helpful.

- They are definitely tone frames. Tones run through the vocoder 
are irrelevant and OP25 would handle them just fine anyway.

- Why should the user seek other solutions? The system is sending 
IMBE tone frames and any decoder thrown at it should handle it.

- And how does simulcast have anything to do with this? It doesn't.

To the OP: You need to record the raw signal (I/Q data or FM 
demodulated audio) so someone can analyze it. Then the decoder logic 
can be updated to accommodate tone frames and you'll get your audible alerts.

At 04:19 PM 16-06-2018, 'William Becks' wllmbecks at gmail.com [op25-dev] wrote:
>What exactly are you trying to determine about the tones?  They 
>appear to be “Alert” tones sent by the dispatch operator ahead 
>of the voice message. I don’t think they actually serve as a 
>signaling function as would commonly be found in analog paging systems.Â
>I believe that someone has already stated that there are only a 
>handful of specific tones or tone combinations that are provided for 
>in the P25 vocoder. Any other tones or tone combinations 
>transmitted into the speech input of the vocoder quote likely will 
>not reproduce and exact replica as the source tone(s) primarily 
>because the vocoder is designed to encode and compress speech.
>Bill, WA8WG

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