[arm-allstar] Linear vs. Log audio plots

[Josh W4ZZK]

Doug/David,

The audio issues I was having in relation to this has been resolved.
Working A+ now.  Thanks for your great work gentlemen.

73
Josh W4ZZK

On Mon, Oct 2, 2017 at 5:29 AM, "David McGough via arm-allstar" <
arm-allstar at hamvoip.org> wrote:

>
> Hi Everyone,
>
> To give a little more background, by default, the "linear" TX level
> calculation is used only for the original CM108 (PID: 0x000C, original
> URI, some clones). Otherwise, the "log" calculation method is used.
>
> Several weeks ago a ham was having problems fine-tuning the TX audio
> at very low levels. He had a chip where the "log" level adjustment was
> getting applied, so, I forced the driver to use the "linear" method. And,
> then I forgot and left that code in there (oops!).
>
> For this application (i.e.: setting the deviation level of an FM
> transmitter), I think it makes more sense to leave the adjustment method
> "linear," however, that obviously will disturb audio levels for existing
> installations, where the driver originally selected the "log" method.
>
> BTW, if this application was to adjust the volume driving a speaker, the
> log level method (AKA: "audio taper") is preferred, since the human ear is
> a logarithmic device!
>
> Anyhow, now you can selectively force the simpleusb driver to use the
> method you prefer, rather than just accepting the defaults. This setting
> may also ease transition from original CM108 chips to other varieties,
> like the CM119A found in the URIx and Repeater-Builder RIM products.
>
>
> 73, David KB4FXC
>
>
> On Mon, 2 Oct 2017, "Doug Crompton via arm-allstar" wrote:
>
> > Dave did some plotting of the TX audio level changes using the linear and
> log methods. As expected they are quite different. The linear has better
> spread in the high and low extremes and the log in the center. I might
> point out that many of us are using the newer URI which by default would
> use the log method and would have little adjustment at the ends of the
> 1-999 range. The linear may be preferred but since this hack has been in
> the code for so long we are leaving it in as default but giving you the
> ability to select linear or log manually. Here are his comments and graphs.
>
> ------------------------------------------------------------
> ----------------
> Here are GNUplot graphs showing the linear and log modes of TX audio level
> adjustment. The log mode seems whacky to me, but, I verified that is the
> correct formula used in the channel driver!
>
> NOTE that the CM1xy mixer range is 0 to 152.
>
> Linear calculation (old URI cards and tx_audio_level_method == 1):
>
> https://hamvoip.org/photos/Gnuplot-TX-method-1-linear.png
>
>
> Log calculation (any non-cm108 adapter):
>
> https://hamvoip.org/photos/Gnuplot-TX-method-2-log.png
>
> 73, David KB4FXC
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