[Elecraft] K3 RX Audio

[David Woolley]

Tree wrote:

> http://www.kkn.net/~tree/160/3b7cQSO.mp3

MP3 is probably not a good choice for critical evaluation of the audio 
of a DSP based system, as it involves heavy additional DSP to  produce 
it.  In particular, MP3 works by limiting close in dynamic range 
(because the ear cannot hear weaker sounds close to a strong one), so 
weak signals which are close to strong ones will be reproduced with 
worse resolution, or lost.  (It's a bit more complex than that as it is 
done on frequency blocks.)

It's also a block based encoder and, although I'm not sure, it is 
possible that it loses phase information and fakes wideband noise.  (I 
presume it must retain low frequency phase information, for stereo to 
work, but I don't know if it encodes I and Q in all frequency bands or 
whether it falls back to just power at the higher ones.)

Even if it retains phase, I wouldn't expect it to reproduce multi-tone 
or, in particular, noise like digital modes well, and if you can hear 
subtle DSP artefacts in the K3 you can probably hear those resulting 
from MP3 encoding.

Unfortunately, doing an extra A to D / D to A pair is inevitable, given 
there is no digital output, but it needs to be done at a carefully 
chosen sample rate.
-- 
David Woolley
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