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Digital Voice Formats Discussions regarding different digital radio voice formats, including AMBE, IMBE, VSELP, GSM, CELP, MELP, and others.

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Old 03-03-2014, 3:31 PM
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Default Difference between IMBE and APCO-25?

I have seen different threads talking about IMBE and APCO-25 digital voice formats. What is the difference between the two? Where are they used?
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Old 03-03-2014, 4:19 PM
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APCO 25 is the name for a set of standards. That standard happens to use the IMBE vocoder which is another way of saying a digital voice synthesizer.
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Old 03-03-2014, 4:30 PM
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Thanks for the reply. So .. would it be safe to say that just because a radio makes use of the IMBE vocoder does not make it a P25 radio? But if a radio was P25 compliant it would have to use IMBE for the vocoder?
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Old 03-03-2014, 4:49 PM
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Quote:
Originally Posted by human8472 View Post
Thanks for the reply. So .. would it be safe to say that just because a radio makes use of the IMBE vocoder does not make it a P25 radio?
That's correct. The ProVoice implementation uses the IMBE vocoder, but is certainly not P25 compliant. It uses different modulation schemes, error correction, etc that is covered under the P25 standards.

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Originally Posted by human8472 View Post
But if a radio was P25 compliant it would have to use IMBE for the vocoder?
For Phase I (FDMA) usage, correct. Phase II (TDMA) uses the AMBE+2 vocoder since it works better at a lower bitrate.
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