[arm-allstar] DSP & RPi2

[David McGough]

Hi Dave,

All the code to run usbradio is included in the RPi2 release. However,
while better than on the BBB, I'm "luke warm" about the performance. With
my "mix" of settings, I hear a rather large number of pops and clicks
(AKA: choppy audio), as compared to usbradio on a fast PC. These problems
are in addition to the other typical usbradio audio artifacts Doug has
mentioned.

I agree with you that there is a huge need for high-performance DSP
capability (PL/DPL encode/decode, Squelch, filters, compressors/limitors,
etc.). I -personally- need this capability for projects I'm working on.

So, a fix is in the works, via a new channel driver. I won't get deep into 
the details, but, I will mention that it implements a modular, 
multi-processing approach. This allows it to take more advantage of the 
new multi-core CPU's that are now so prevalent (and the trend of the 
future).

For now, simpleusb works quite well. And, the latest code includes full
flat-audio (de-emphasis and pre-emphasis--thanks Jim!) support, and a RX
audio delay feature to chop off squelch tails. I will mention that some
users (including ME) have noticed a variable audio delay between RX and TX
audio, when used in duplex=2 mode (a repeater). This problem seems to show
up when the node is actively linked to some other node.  I've got a
work-around for this issue and it will be included in the next release.

These are FUN little boards!

73, David KB4FXC



On Tue, 28 Apr 2015, David Kavanagh wrote:

> Hi All
> 
> I was wondering if someone may be able to advise if anyone has had 
success as yet in getting DSP up and running on the Pi2? I have heard of 
some people having "choppy" audio and yet some apparently have it running 
fine.
> I would love the facility to change/swap CTCSS and other details simply 
thru the software and the better quality audio that also comes with the 
USB Radio driver and use flat audio into the URI/software.
> 
> I see there is the usbradio.conf file there to be played with but do we 
have any facility to try this on the current version? Would changing the 
rpt.conf to usb/radio allow the driver to be utilised or are there other 
dependancies to be installed? Is there a tune "helper" facility available 
to assist in setting the audio levels in the software etc - I have had a 
look around however I am unable to find it as yet.
> 
> After all - that's what its all about - trial and error or "crash management" 
> 
> Look forward to your replies.
> Dave
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