[arm-allstar] How to adjust the audio characteristics for both TX and RX?

[David McGough]

Hi Irv,

The simpleusb (or usbradio) preemphasis (hi pass) and deemphasis (lo pass)  
settings adjust IIR digital filters in the channel driver code. These
filters have static, compiled-in coefficients, so there is no way to
adjust them other than just enabling or disabling them.

Your IDAS system has "speaker" audio input and output, so, you will
probably want to leave preemphasis=no and deemphasis=no on the AllStar 
side.

Some digital radios have audio equalization settings which can be tweaked 
a bit. I don't know if the ICOM radios have this capability. I know 
various DMR radios can be tweaked via the RSS software.

I don't expect you'll gain very much by trying to equalize the audio AFTER 
it has passed thru the AMBE+2 low-bandwidth CODEC used by most digital 
radios (like IDAS). The best plan is to try to adjust the settings in the 
radio proper....That, or go back to analog FM, which will comparatively 
sound fantastic!

73, David McGough




On Thu, 30 Nov 2017, "Irvin Fontanes via arm-allstar" wrote:

> Doug,
> 
> This is a private node. Just me as a user. It is used as follows:
> 
> -Rpi 3 connected to an arcom rc-210 on port 2
> -icom fr-6000 on port 1 running idas 6.25 khz bw
> 
> The setup is configured so that I talk into the fr6000 with an icom
> ic-f4261dt and it gets piped (in analog from the back of the db25) out to
> my other private node.
> 
> I know that the audio quality takes a toll when digitized and there's
> nothing I can do about it; however; I'd like to experiment with whatever
> code/script is called out when preemphasis=yes or no and deemphasis=yes or
> no is selected since when the audio gets converted back to analog (out of
> the fr6000's db25) it is missing some of the"highs".
> 
> So, could someone tell me which script is called out when preemphasis=yes
> or no and deemphasis=yes or no is selected? I would seriously like to
> experiment.
> 
> Thanks,
> Irvin
> 
> Irv,
> 
>  Pre and de-emphasis is a fixed equalization designed around FM
> communications standards. You cannot nor should you change that. Also using
> pre or de-emphasis just to tailor audio is not a good idea. It should be
> set correctly for the radio you  are using. There is currently no
> equalization capability in Allstar within its self it is basically flat. In
> the future there may be a way to do equalization in the IOpipe channel
> driver. If you have a circuit, transceiver etc. that has poor audio
> characteristics it is best to try and fix that rather than trying to
> correct it with SW. The other issue is every radio would have different
> characteristics and if you have a node that has multiple users you would
> just be chasing your tail trying to get things right for each user or radio.
> 
> 
> *73 Doug*
> 
> *WA3DSP*
> 
> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio
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