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Old 10th August 2017, 10:50 AM   #291
Ivo is offline Ivo  Netherlands
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Oh, and a question about the kernel hacking. I see that in the kernel, the bitrate is also defined. We change the samplerate and number of channels, but not the bitrate. Can we also change that and what would be the right code for that? Simply changing 16 to 24? Or is it more complicated than that? If you check the capability of the HDMI hardware, it says 24/192 is possible, but as far as I can tell the kernel as it is now puts out 16/192.
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Old 11th August 2017, 02:31 AM   #292
francolargo is offline francolargo  United States
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Originally Posted by Ivo View Post
The stuttering issue, and lower pitch, seems to be caused by the re-sampling process eating up too much processor resources. If I choose a different resampling algorithm that is lighter, it reduces or disappears. Perhaps there is also a conflict between Jack and VLC, in the sense that they have some real-time priority settings and this might not work too well. Maybe if I untick real-time in VLC, it would also help.
Thanks for the update! I imagine that VLC needs as much priority as it can get, so I would expect real time status to be most satisfactory. If you can increase the buffer size that might also help. Which program is initiating the resampling? If you can eliminate that processing you will definitely save CPU. With HDMI out, shouldn't any reasonable sample rate be acceptable? The LADSPA filters adapt to changes in sample rate without problem if run within ALSA's user space. If JACK is causing resampling (which I doubt), I would consider using Alsa instead, and just suffering through the process of managing the various streams.
Quote:

I have an extra pi now and am looking into setting a master-slave relationship in Jack between the two pi's. So that one pi plays the media into jack, jack transports it over the wired network to the other pi where processing is done. Jack then sends it back to the original pi and to the AVR over HDMI. That way, I hope the processing pi is most robust and the playing pi can be set to optimal re-sampling settings etc.
THAT would be very cool if you get it working! To my knowledge it would be a first...
Quote:
Right now, it simply works, but it is not usable enough for the family living room.
I know how the complexity of these systems seems to grow exponentially. I solved this in my system using a program called NetIO, which allows any iOS or android device to become a remote control. Then using python scripts, changing many operating parameters at once is as simple as a button click. I even use it with I2C to address my DAC chips and control volume at that point in the chain. With NetIO there would be no need to activate the system GUI. I have examples of script code for my BBB on GitHub, and there is a thread here Control of BBB-based audio appliances

Finally, regarding your other question, I have never tweaked a kernel so can not help.

Cheers,

Frank

Last edited by francolargo; 11th August 2017 at 02:35 AM.
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Old 11th August 2017, 09:19 PM   #293
Ivo is offline Ivo  Netherlands
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Originally Posted by francolargo View Post
If JACK is causing resampling (which I doubt), I would consider using Alsa instead, and just suffering through the process of managing the various streams.
Jack runs on a set sample-rate. My biggest reason for using Jack, is the graphic interface. I build loudspeakers and to "code" a crossover and EQ together every iteration is not the fun part of playing with this. The Hypex and MiniDSP interfaces are what you want if you are a loudspeaker hobbyist first. Jack is messy to get going on a pi (for my and my particular lack of knowledge and learning curve), but it sets up in minutes on a x86 linux computer and after that fooling around with channels connections and plugins is very intuitive and easy.

Jack also tightly controls synchronisation between channels and processes, even over network connections. It is actually used for instance in studio situations with small silent clients in the studio/control room and the big noisy recording/processing computer with hard disks and fans in a cupboard or the basement. It has that level of reliability and tight sync.

Really, after what I learned, next time I would advise somebody else to but an Intel NUC and run KXstudio on it. Everything ready to roll, Jack and plugins and plenty of computing power left to play and transcode media. But so far this has been so much fun and so educational. A hobby of its own.

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Originally Posted by francolargo View Post
THAT would be very cool if you get it working! To my knowledge it would be a first...
Error using jackd on RPI3 - Raspberry Pi Forums

Note you could go so far as to split all channels and have a whole pi per channel available for DSP. Or string a number of pi's to do more channels. Convolution with LOTS of taps. I mean that's absurd at some point, but this does open up possibilities.

Quote:
Originally Posted by francolargo View Post
I know how the complexity of these systems seems to grow exponentially. I solved this in my system using a program called NetIO, which allows any iOS or android device to become a remote control.
Very interesting. I'll check that out.

If the next version of Kodi does all that is planned, that would be great, has some very usable remote control apps.

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Finally, regarding your other question, I have never tweaked a kernel so can not help.
No problem, will keep looking.
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Old 12th August 2017, 02:31 AM   #294
francolargo is offline francolargo  United States
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Pretty interesting stuff! Your approach has quite a different focus from others I've seen involving the RPi. Both it and the BBB have the ability to input an external master clock. By selecting the appropriate frequency multiple, no resampling is necessary in the process of rendering different music files to real time. The sonic benefits of that are well recognized. The Botic kernel that I use switches between two different oscillators depending on the native frequency of the particular file being played. But you are gaining other attributes that suit your system, so why not? Proost!
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Old 29th December 2017, 06:55 PM   #295
Ivo is offline Ivo  Netherlands
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Just a very small update: there is a kernel hack at github for multichannel over HDMI *and* higher sample-rates and bit-rates. I recompiled with that and get fewer issues with xruns etc in Jack. DSP load is a bit lower as well, it seems. I see there are a few more changes here and there in the kernel, annotated stating it's necessary for higher sample-rates. I am guessing the simple hack really only facilitated the multichannel part and that a high sample-rate set in Jack (higher than 48kHz) could not be output over HDMI and had to be re-sampled again. The hardware is more capable than we think, but the software/firmware is not there yet. The hobby space. :-)

PCM sound on HDMI output: Support higher sampling rates up to 192 kHz, 24 bit depth, 5.1 channels by soundg33k * Pull Request #1834 * raspberrypi/linux * GitHub
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