[ICOM] Bad TX audio on 775

[Art]

Please don't use the word 'compandering' when discussing amateur 
radio transceivers. It is a completely different matter to use 
compondering and to the best of my knowledge, there is no amateur 
radio commercially made gear that uses compandering. Compandering and 
compression are not the same, not even remotely so.

Compandering is a very extreme form of compression, but it goes way 
past what compression actually is.

In amateur radio, we boost the middle voice band frequencies as they 
convey the bulk of the intelligibility and for communications 
quality, we can live without dc to 400 Hz and 2500 Hz to 5000 Hz. 
Using compression sacrifices some fidelity and does make the 
transmitted bandwidth slightly narrower than a non compressed signal. 
This gentile massaging of the bandwidth needed to transmit a readable 
signal is called compression, and is NOT called compandering.

Compandering is a completely different ball game. To use 
compandering, the 'normal' 300 to 3000 Hz audio frequencies are 
'converted' to different frequencies and then transmitted (over a 
narrower bandwidth channel). At the other end, the received signal is 
un-compandered and converted back to it's original 300 to 3KHz 
communications quality audio. For instance.........

These days we have DSP. DSP can take the 300 to 3000 Hz audio input 
and convert it to 300 to 400 Hz audio. Of course, this audio would 
not be usable to the human ear. But, the advantage is that the same 
audio information can now be conveyed by a 100 Hz bandwidth 
communications channel so LESS NOISE or interference is present. The 
receiving end takes the 300 to 400 Hz stream and converts it back to 
300 to 3 KHz so it can be listened to by a human again.

Early compandering efforts in the 70's were a dismal failure, and 
Motorola (who invested millions in it) finally abandoned all efforts 
to use it. In those days, they simply didn't have the DSP technology 
that we have today...so it didn't work. They tried to use analog 
methods to achieve compandering-you can imagine how crude it was::> 
However, they still hold the patent(S)::>

Today amateurs with stand alone DSP units or PC's with soundcards can 
experiment with compandering, but I am unaware of any commercially 
made amateur radio that uses true compandering. Please correct me if 
I'm wrong, it has happened before::>

In the meantime, please don't use the term 'compandering' if you 
really mean 'compression'. To do so would be like comparing a camp 
fire to a nuclear explosion...they just ain't the same::>

Regards,

Art









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