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How fast are decodes

Luke Berndt <lukekb@...>
 

I have a system setup to record a trunked radio system. At times I am recording 3-4 P25 voice channels. I am doing the decode in software but it needs a lot of CPU. I am interested in using the USB dongle. I was thinking of capturing the raw streams and then passing them through the dongle. How much faster than real time is the decoder? How many simultaneous recordings could I have going on and still keep up? Would it changes with p25 phase 2?

Sent from my iPhone

myyahoo@...
 

You would need a dongle per stream, the dongle can only decode one stream at a time.

Given the price of dongles, you might want to try a hybrid approach, and offload a stream or two and do the others in software?

- Richard, VE7CVS

"John D. Hays" <john@...>
 

Luke,

Richard is correct, the AMBE3000F chip in the ThumbDV is a single stream vocoder.  It only vocodes the audio stream, not the P25 (or other transport) protocol.

Since it is a USB device, you can plug in several which will each appear on their own "COM" or "tty" device to the OS.   Plug in as many as your computer / OS / USB busses can handle for parallelism. Each appears as a 230.4 kbps serial device.

Your software will need to remove the AMBE stream from the P25 protocol (for each channel), buffer it into packets and send it to the ThumbDV, for each packet of AMBE it will return a packet of PCM encoded audio back (and visa-versa).

It will not decode IMBE (P25 Phase 1), only P25 Phase 2.

On Thu, Feb 5, 2015 at 11:52 AM, myyahoo@... [UniversalDigitalRadio] <UniversalDigitalRadio@...> wrote:
 

You would need a dongle per stream, the dongle can only decode one stream at a time.

Given the price of dongles, you might want to try a hybrid approach, and offload a stream or two and do the others in software?

- Richard, VE7CVS


--


John D. Hays
K7VE

PO Box 1223, Edmonds, WA 98020-1223 
  

lukekb@...
 

Ah! That is good to know about IMBE vs AMBE. Right now I am using OP25 and it doesnt look like it is too tough to dump the packets at the right level.

How much faster than real time can it decode a packet? How long would it take to decode 10 seconds of audio? Would it be 10 seconds? I am trying to figure out how many recordings I could queue up and have it keep pace.

"John D. Hays" <john@...>
 

I don't have any data on speed of actual decode time.  These chips are usually used to handle one stream in slightly delayed real-time (e.g. they can keep up but there is a small amount of compute delay between input and output).  Also the ThumbDV is tied to a 230.4 kbps transfer rate.  I would plan on one ThumbDV per stream.

The DV3000 (GPIO version) can use trace-cut / jumper to increase the bps on the serial interface, but anything along that path is pure experimentation.


On Thu, Feb 5, 2015 at 2:53 PM, lukekb@... [UniversalDigitalRadio] <UniversalDigitalRadio@...> wrote:
 

Ah! That is good to know about IMBE vs AMBE. Right now I am using OP25 and it doesnt look like it is too tough to dump the packets at the right level.

How much faster than real time can it decode a packet? How long would it take to decode 10 seconds of audio? Would it be 10 seconds? I am trying to figure out how many recordings I could queue up and have it keep pace.




--


John D. Hays
K7VE

PO Box 1223, Edmonds, WA 98020-1223