[arm-allstar] New Channel Driver Code in Debelopment

[Patrick Perdue]

SVXLink operates at 16 kHz.

Yes, I can definitely hear a clear difference, even on FM, at least with 
some radios. Yaesu comes to mind. Those radios tend to cut off closer to 
5k than 4, so listening to a Yaesu over SVXLink sounds more like 
simplex. Granted, I've only actually heard this in recordings of SVXLink 
demonstrations.

With the pervasiveness of Baofengs though, I don't know how many would 
actually notice if the sampling rate were increased 2x, and the filters 
adjusted accordingly. Even most analog repeaters I've come across are 
*at least* as limited as 4 kHz, and usually more. I've heard examples of 
better, but it's pretty rare now.

I say all this as someone who is in favor of using 16 kHz audio as a 
backbone for FM via VoIP, at least in theory. Most probably wouldn't 
notice or care, and it would make the most difference when linking 
well-tuned repeaters together, which is exactly how SVXLink is being 
used, though I don't think it's very popular in the U.S. for that 
application.

HamVoIP does support G.722, but I think this is mostly for compatibility 
reasons, and won't actually do anything to increase the frequency 
response when using radios due to a well-done implementation of low 
pass/anti-aliasing on the simpleusb driver, among other things. Having 
used ASL, which doesn't have as good implementation in comparison, I 
definitely do appreciate that. Maybe if everyone is on a VoIP phone set 
to G.722, you'd notice.


On 4/29/2022 5:37 PM, "M Lech via ARM-allstar" wrote:
> While we're at it, can we implement 16KHz sampling instead of the crummy
> 8KHz sampling ? I'd think I'd died & went to heaven to have the audio
> bandwidth matching our RF links. For me this is huge. The hardware has no
> problem doing it, so why don't we? Thanks in advance!
>
> 73,
> Matt W6XC
>
> On Fri, Apr 29, 2022 at 9:27 AM "Dave Petrie via ARM-allstar" <
> arm-allstar at hamvoip.org> wrote:
>
>> Hi David, just curious if you made any progress with the new channel driver
>> code in development so that chan_simpleusb can send and receive CTCSS like
>> usbradio does. Here is what I found that led me to ask the question.
>>
>> On 9/5/21 11:41 PM, David McGough wrote:
>>
>> Hi Jim,
>>
>> CTCSS generation isn't currently in the chan_simpleusb code. However, it
>> is in new channel driver code in development.
>>
>> All the original usbradio related code and features are in HamVoIP. So,
>> that should work, if you can tolerate the sporadically glitchy sounding
>> audio.
>>
>> How quickly do you need this?  I can probably get you info on the new
>> channel driver in a few days.
>>
>>
>> 73, David KB4FXC
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