[Elecraft] K3 Questions

[Corboy-Poteet]

David. let me pose a question: if you converted the digitized voice
signal to mp3 or ogg format, is this similar to (or the same as) a
freq domain data stream?  The data compression from CD wav file to mp3
is around 10 to 1; you are certainly not storing a digital copy of the
sound wave.  Voice compression may not be so good but still should
result in the need to transfer considerably less data in order to
assure a useful voice recovery on the receiving end.

Mike  W5FTD





> Stuart Rohre wrote:
>> In the basics of digitizing the signal you have to clock the conversion at 
>> least twice the highest frequency you want to reproduce in the voice (or 
>> audio) signal.

> That's only at the input to the encoding chain (and technically it is 
> twice the bandwidth, not twice the highest frequency).

> However, I would imagine all digital modes that would be used for 
> communications, rather than broadcasting (and for that matter, also 
> those used in modern broadcasting systems) don't send time domain data.
>   One way or another they send frequency domain data, often in the form
> of just the formant frequencies used in a model of vocal tract resonances.

> The critical rate for these systems is the syllable rate, not the 
> frequency of the highest component.  I seem to remember that the 
> military were using 2400 bits per second codecs maybe a couple of 
> decades ago.    I suspect that was partly do do with how fast they could
> encrypt.

> Mobile phone codecs tend to be vocal tract model based, although they 
> use more than 2400 bps so that the voice sounds reasonably natural (but
> try them on modem tones or even music!).

> To get much better than 2400 bps, I think you would probably have to 
> recognize phonemes, which is basically the continuous speech voice 
> recognition problem.  I think that might get you down to about 300
> bits per second.