jackd starting and RT Kernel for Wolfson

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jackd starting and RT Kernel for Wolfson

Postby puredyne » 19 Sep 2014, 20:15

Hello everyone,
In two days I will be introducing my first Raspberry.

Unfortunately it does not seem to work properly to play the audio and sound. In comparison to my Linux DAW, in addition to losing detail, dimension, dynamic and naturalness... Compared to my usual MPD@WS,via RME_HDSP@Jack, the SPDIF Out of the Wolfson PI also the full volume is reduced.

Unfortunately I have not managed to start jackd... could you please give me some advice?

I noticed that the RT Kernel for the Wolfson Card has an unusual setting... how did you set the timer frequency 100HZ? The Audio Kernel, Low Latency or Real Time, have always been set to 1000HZ.

Would kindly provide me with a link to the source and configuration file, to recompile and test the linux-rune-3.12.13-rt21_wosa.img with 1000HZ?

Code: Select all
# CONFIG_HZ_100 is not set
# CONFIG_HZ_250 is not set
# CONFIG_HZ_300 is not set
CONFIG_HZ_1000=y
CONFIG_HZ=1000


Furio
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Re: jackd starting and RT Kernel for Wolfson

Postby cmh714 » 19 Sep 2014, 21:46

for volume, ssh in and run alsamixer. the volume could be set too low or muted totally.

F6 chooses the sound card, arrows for volume and the "M" key for mute/unmute.

not sure I can help on the jackd, but have used it before on ap-linux
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Re: jackd starting and RT Kernel for Wolfson

Postby Midnight » 23 Sep 2014, 15:15

For audio playback you won't need low latency. So you neither need a RT kernel, nor 1000 Hz.
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Re: jackd starting and RT Kernel for Wolfson

Postby puredyne » 23 Sep 2014, 21:12

Midnight wrote:For audio playback you won't need low latency. So you neither need a RT kernel, nor 1000 Hz.

A Linux Player without a good RT Kernel & without a Jack sounds terrible. It seems obvious to me that only this combination can minimize the various jetter problems caused by the operating system.
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Re: jackd starting and RT Kernel for Wolfson

Postby Midnight » 23 Sep 2014, 21:23

I respect your opinion, but tell me more about these magic kernel facts :roll: :mrgreen:
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Re: jackd starting and RT Kernel for Wolfson

Postby puredyne » 23 Sep 2014, 22:27

are the same similar problems of a cd player, windows, osx, etc ... with the samples you can hear everything!
theories do not make sense. linux audio exists and it sounds better than records and tapes for over 10 years. not like or worse.
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Re: jackd starting and RT Kernel for Wolfson

Postby ACX » 24 Sep 2014, 00:32

Hi everyone,
I suggest you to take a look at the following interesting resources before starting a flame :)

About the real need of a RT kernel:
https://wiki.archlinux.org/index.php/Pr ... ime_Kernel
http://jackaudio.org/faq/realtime_vs_re ... ernel.html

About the real need of JACK in a simple playback application without multiple streams mixing:
http://wiki.gentoo.org/wiki/ALSA#JACK_A ... ection_Kit

Anyway, @puredyne: if you want to experiment a RT setup with JACK we'll be pleased if you decide to share your results with us. MPD already has JACK input plugin enabled since RuneAudio 0.1-beta.

About the 1000Hz issue, we have to check it (soon we'll publish all the configs).
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Re: jackd starting and RT Kernel for Wolfson

Postby puredyne » 24 Sep 2014, 09:59

Today, many are hoping to overcome the jitter problems with asynchronous technologies.

At the time... I lost the motivation to continue to spend time and money with USB.

I'm most interested to try a direct I2S connection.

I only found this old analysis: http://www.nexthardware.com/forum/cmp2- ... zioni.html
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Re: jackd starting and RT Kernel for Wolfson

Postby ACX » 24 Sep 2014, 12:22

puredyne wrote:Today, many are hoping to overcome the jitter problems with asynchronous technologies.

At the time... I lost the motivation to continue to spend time and money with USB.

I'm most interested to try a direct I2S connection.

Ok, you are focusing on a different problem now, as this involves a different type of jitter - the so called "interface jitter" (take also a look at this article which I tranlated some time ago and which explains it in a simple way).
Going I2S will solve some problems for sure - you are bypassing the interface jitter of the USB transport and the USB > I2S conversion. That's definetly the best approach expecially for the Rpi platform, with its well known USB/Ethernet issues.
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Re: jackd starting and RT Kernel for Wolfson

Postby puredyne » 24 Sep 2014, 19:18

OK, thank you for all the answers and the interesting links!

So I would start with the preparation of linear power supplies... and thinking on how to separate the sound card.

If someone could tell me on how to be able to start Jack, I'd like that. How I would love to see jack sample parameters.

A sentence of the last article sent me into paranoia.

"Possiedo un ricevitore con 200 ps di jitter che suona molto meglio di un altro con 50 ps, MA la loro risposta in frequenza è molto diversa.Quindi scegliere il valore di targa di jitter più basso non è garanzia automatica di suono migliore."

50 ps? I can think only of the Wolfson's transceiver.
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