[arm-allstar] Distorted audio (sampling?)

[Alessio Sacchi]

Hi all,

I am new to the forum and (relatively) to hamvoip. I come here for help
after a long journey. Last spring I decided to pick up a project I started
in 2014 for my local club. I procured myself 5x URI back then for the
project. I was running TLB back then, so this year I tried OpenRepeater,
ASL, then finally landed here as I couldn't get more that 1 port to work
without distorsion with ASL. I have to say I have faced several challenges
with hamvoip but I was able to get out of it just using documentation and
forums. So congratulations to all of you for enabling folks like me to get
to a successful setup alone.

I finally decided to move my node up to the repeater location last Saturday
and move it to "production".  The node is running 1.5rc6-10 on a PI 3B. I
have 4 ports running: Echolink, a 70cm duplex=2, a 50MHz duplex=1, a 1296
MHz duplex=1 via DMK URI. I am using simpleusb.
In my setup, Echolink, 50 and 1296 are connected to my 70cm port at all
times - the desired behavior is for my users to get out on all other ports
regardless of where they come in. It works fantastically with distinctive
courtesy tones and short tails.

I have minor configurations things I will need your help later on, but one
thing is really impacting usage and adoption. We are experiencing
occasionally distorted audio when audio comes from radio ports.

I believe the issue manifests randomly (or at least I have not found any
periodicity) but has the same "form" when it happens.  I have uploaded some
recordings here on dropbox
<https://www.dropbox.com/sh/jbmsbhuh2ebqi7l/AADXRBT9IVz8IbHittoqLW_na?dl=0>
.

Look at the filename for time reference t the issue in each file. As you
will notice, the issue manifests in a fade up and fade down form all of the
times. I am tempted to describe it as progressive packet loss when
sampling. I was able to confirm this happens only when sampling from URI's
- a signal getting in from Echolink will be repeated on all output ports
just fine at all times. It also happens on all ports - meaning your signal
may be affected regardless the of the audio getting in from either one of
the 3 radio port. However - and oppositely to what I just said - I have
just heard one case where the voice beacon was similarly distorted.

I questioned myself whether the PI load was too high. It doesn't seem to be
the case. asterisk is using just above 70% CPU in the worst case scenario.
I did try to remove load - for instance by disabling recording which I am
sending to a mounted exfat USB stick on the 4th USB of the PI. I also tried
to unlink 23cm and 6m from 70cm to reduce the I/O toward USB, but no luck.
I did not try to remove the 2 ports physically yet as you can imagine being
a remote site.

I read through the forum and found out some important work on variable
audio delay was done recently. I would be curious to know if the problem
this was generating had a similar behavior - and most importantly how many
ports this was tested on. I have the feeling 3 radio ports are too many for
a single PI - or at least that it is not a common scenario to many, hence
not much tested by the community. Very curious.

I also read an interesting post around audio distortions and PI power
supplies. In my setup, I have a 220Vac to 5Vdc wall plug in adapter bought
off amazon just after a 1500VA APC UPS. I wonder if ripple on this power
supply might be responsible for this issue. Or any other type of spurious
emission picked up from the 5V line.

Core dumps: I do see one generated ~24+ hours after I first booted the
system up on the hill. No other since, so it has been stable for 4 days
although I have been restarting asterisk manually a few times to apply some
configs.

I guess it's enough for now :) Looking for your valuable inputs.

73s and thanks.

Alessio IZ4EFN