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PostPosted: Fri Jun 09, 2017 7:30 pm 

Joined: Thu Jan 15, 2015 11:19 am
Posts: 17
Hi all,

now with ST 8.40 I have a running ST with Jack on Rpi 3.

I'm using AGC, multiband 1 and singleband, nothing else.
Jack is set to 4096/4 on a Focusrite Scarlett 2i4 USB sound card.
I played with lots of ST settings for sound card and CPU, but there are always very short click sounds in the output.
It seems that the clicking is less when I hide the GUI of ST.
Overall CPU load is around 50 %.

Anyone else who has this problem? Or any ideas how to solve it?

I need to use Jack because I will add a few Jack clients to the chain later for control and visualisation.


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PostPosted: Sat Jun 10, 2017 12:17 am 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 8949
Is Jack running in realtime mode? If so, try a higher number of buffers. I haven't tested this sound card yet, and I don't know if the same numbers work on all sound cards.


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PostPosted: Sun Jun 11, 2017 11:08 pm 

Joined: Thu Jan 15, 2015 11:19 am
Posts: 17
Jack is running as root with the RT flag set, so yes, it is realtime
I was able to reduce the clicks by doing the opposite:

Now I have the buffers at 512 / 3, and when I close/minimize the GUI and also remove all other USB devices, the clicks are almost gone.
So I expect this is a sound card issue. I also realised the 2i4 needs 500 mA to operate and I don't have a power supply strong enough for that and additional processor load, so the little yellow spark becomes visible indicating problems with the power supply. No big problem though as I'm going to use a different audio device in the final system.

I haven't yet tested output from an internal audio source and playout via HDMI. Will report my findings here.
Meanwhile all other experiences with audio devices, Raspi3 and ST would be welcome.


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PostPosted: Wed Jun 21, 2017 7:46 pm 

Joined: Thu Apr 27, 2017 3:54 am
Posts: 5
You didn't mention your distribution or kernel version but there are known issues with USB timing on Pi3 and noise as it shares the same bus as the Ethernet adapter.

For best results you should make use of the on-board i2s with adapter cards from hifiberry or others of your choosing. You'll get 192kHz/24-bit that way which is suitable for FM MPX as well if ever that becomes your intention :)


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PostPosted: Wed Jun 21, 2017 10:49 pm 

Joined: Thu Jan 15, 2015 11:19 am
Posts: 17
It already came to me that USB may not be the best option for sound as almost everything on the pi seems to run on USB.
There were some Wolfson audio cards that also had analog inputs. I want to build a stand alone processor with line out and network input straight into jack, but would very much welcome the option of having line inputs as well. It doesn't need FM capability. The Wolfson is no longer available. Do you know of any i2s devices with ADC + DAC onboard?

I'm running latest raspbian with Pixel GUI and it has a 4.9 Kernel.


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PostPosted: Thu Jun 22, 2017 9:54 pm 

Joined: Thu Apr 27, 2017 3:54 am
Posts: 5
I did find this one:

https://www.amazon.com/dp/B01HBC8CJ0

Disclaimer: I have not used it and it looks light on the filtering just from the pictures.

It has enough resolution for good audio without FM so sounds like it would meet your requirements. Other than that since the i2s headers are exposed easily enough you can also hook these on to the many 'development kits' available from the manufacturers. The TI and Wolfson chipsets have pretty good support in the kernel.


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PostPosted: Sat Jun 24, 2017 12:32 am 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 8949
96 kHz, so not usable for MPX unfortunately :(

If you don't need FM, it looks like a good option.


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PostPosted: Tue Aug 15, 2017 5:07 pm 

Joined: Thu Jan 15, 2015 11:19 am
Posts: 17
Ok, so I've continued to experiment with the Pi3 and my USB sound card.

I've found that while there is any more than 15 - 20 % CPU load that the output starts clicking on USB. It doesn't need to be ST, a simple cat /dev/urandom causes crackling, too.
Testchain is: VLC playing a 440 Hz sine straight into the outputs. Start the /dev/urandom output and it starts clicking immediately.

If anyone can try with a different USB sound card, that would be nice.

BTW, StereoTool does not behave while there are no standard jack capture ports available. That makes using any "playback onhain isly" devices hard to use.


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