On 22/04/2019 11:27, The Natural Philosopher wrote:
On 22/04/2019 09:18, mm0fmf wrote:
The issue with DAB is it is an old crappy codec that doesn't compress
the audio as well as modern codecs do. In order to maximise profit,
signals are encoded at very low bit rates and strangled bandwidth to
squeeze more in. So you get the worst of both worlds perfectly
reproduced crap audio and no way to in-situ upgrade to better codecs.

Someone calculated that intelligible speech could, if tokenized, be sent
down a 50bps channel. I.e imagine reduing it to text or sylalables
sending that, and re synthesing a voice at the other end.

I have done it on military systems at 600 bps[1] using a LPC-10 vocoder.
Its far from telephony channel quality, and loses pretty much all
character to the voice, but it is surprisingly intelligible so long as
the speaker is trained to speak with discrete pauses between words.

[1] which could then be sent with FEC and crypto layered on top over
even poor quality HF channels using a radio modem. With frequency agile
transceivers, it made a robust comms channel that was pretty much
undetectable let alone recoverable to the wrong people, and nicely
skirted round most ECM systems as well.


--
Cheers,

John.

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