[arm-allstar] 16KHz wide-band audio ---was: New Channel Driver Code in Development

[David McGough]

Hi Matt,


Thanks very much for your comments about the desire for wide-band audio
support.  I'm really conscious of and concerned about audio quality; not
quite to the level of fanatical...some who know me might disagree with 
that comment. LOL.
 
I fully agree that Hams are in a unique position with our FM gear, since
we CAN run wider FM deviation and still comfortably be within the FCC
regs.  You mention carry overs from bygone eras.  Asterisk was originally
designed to interface strictly with the PSTN, which, as we know, is
strictly an 8KHz world.  That's where this limitation originated.

Asterisk v1.4.x does have some hooks for 16KHz sampled audio, but not full
support. As an example, the G.722 CODEC is included in HamVoIP and works
for pass-through audio. It's also supports transcoding 8K<-->16K, of
course.  This is the only native 16KHz CODEC typically found in v1.4.x,
however.

The **BIG** stumbling block is that the current app_Rpt module uses the
Dahdi kernel module for mixing/bridging.  Dahdi (again being for PSTN
interfacing) is strictly 8KHz....This being said, eliminating the need for
Dahdi entirely is definitely on my To-Do list. This change would remove
the 8KHz choke-point and make porting the code to new platforms SOOOO much
easier, too!


73, David K4FXC



On Sat, 30 Apr 2022, M Lech wrote:

> David,
> 
> The majority of our infrastructure is in fact customized GE MASTR II
> stations in a form factor called the "uMASTR II" (micro). This is a 2RU
> shelf using the original R/T 'door' of a MASTR II station. Entirely
> replaced wiring harness, modded squelch circuit, modulator modification, a
> few idiot lights, and native controller interface among other options. They
> can mate with a rear-mounted PA up to 30W or separately mounted HPAs.
> 
> Other radios range from Motorola CDMs, Maxtrac/GM300s, GE Orions, GE Exec
> II and MVP, Motorola MSF 5000, Kenwood TKR-850, TKR-820, Spectracom MX-800
> and a Midland BaseTech II. Each type has been analyzed & an interface
> method developed meeting our specifications. We aim for what some call
> "simplex quality" system throughput. Care is taken for level, response &
> minimal distortion.
> 
> Overall the radios implemented have little trouble meeting our
> requirements. High-frequency compensation networks or comp mods inside the
> control systems are sometimes needed for true flatness. The alignment of
> these radios can have a real effect also. GEs benefit very much from a
> fresh IF alignment. Transmit wise, we have a mixture of Phase Modulated and
> (direct) Frequency Modulated exciters.
> 
> The 8KHz sampling is in my mind left over from the bygone era of low
> bandwidth Internet. Remember dial-up? We're not constricted by that any
> longer. Echolink has the same and worse problem of fidelity. It was
> designed for the dial-up era. Likewise, we're not using 486s for horsepower.
> 
> Realizing the current audio bandwidth is "good enough" for most, I realize
> it's maybe an uphill battle. As a wise man once said, "You can't be told
> yes if you never ask." Were coding in that environment a better honed skill
> for me, I'd jump in with both feet!
> 
> Short story, I'd love to see this highly successful medium be better yet.
> Not only for us, for everyone.
> 
> All that said, as Will Roger's once said, "Never miss a good opportunity to
> shut up!"
> 
> W6XC
> GRONK Radio Wild Man
>