[Linrad] Re: Duplex

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Alberto,
>
>     just open the Windows mixer by double clicking on 
> the small loudspeaker icon in the tray are.
Oooh! There is no little loudspeaker. There is another icon
and when I click it I just get the master volume control.

Now I discovered I can right-click on it and get a menu from
which I can select something with some similarity to
what you show on your web page.

Not much joy however. 
http://www.sm5bsz.com/ac97.jpg

On the Linrad waterfall, the bottom half is before I pressed
the mouse to start the output. The upper half with a much higher
wideband noise is with the output running. I have a tone generator
connected to the microphone input and sweep it across the selected
frequency.

The loudspeaker signal is at 20.5 kHz (with h high pitch for the BFO)
and the noise disappears and becomes replaced by the signal as the signal
passes the baseband filter.

The signal level is low, about 8 bits only for the output.
The noise is not really the noise from the baseband but
a heavily distorted signal. The third overtone is at about
13kHz on the scale. If I select 8 bit output, the effect is the same as
switching off the output if I make the level low enough to stay
within the same bit all the time.

It all looks like software bugs to me. Under Linux the behaviour is
a little different, but not acceptable.

After reading a little on the Internet I find it better to
get some more soundcards:-( It seems to me that the hardware
is fine but that the softwares are not correctly written.
Distorted audio seems to be a common problem among gamers
and I find such problems on the AC97 with some settings.
(I tried every combination of everything - I think)

Anyway, what you see is a (buggy?) simulation of something
else and there is no information given to you:-((

Another example. On my laptop I tell Windows I want 48 kHz
and surely that is what I get into Linrad. I can see from the
frequency response and aliasing that the sampling is actually 
at 16 kHz. Maybe the hardware is 48kHz and Windows decides
for mr that 16 kHz is more appropriate and downsamples.
If it does, it also upsamples again for me.

When I switch to the line input, the sampling speed becomes
48 kHz all the way from the A/D converter into Linrad.

Maybe we could have a look when we meet in Florence:-)
I guess there will be several laptops around with different
versions of AC97.

   73

 Leif  / SM5BSZ



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