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Old 26th February 2014, 08:22 AM   #181
syklab is offline syklab  Hong Kong
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I just got a BBB delivered yesterday and have been looking around on how to get I2S output from it, I haven't seen any new release from Volumio which might address the I2s payback for BBB yet, is it coming soon? Any hint from expert?
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Old 26th February 2014, 11:43 AM   #182
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Quote:
Originally Posted by ChrisMmm View Post
Russ, if I understand correctly others have observed 44.1khz being upsampled to 48khz by the current drivers as a result of a restriction of the BBB board clocks, thus unable to produce bit-perfect I2S signal from a typical CD based input file.

Do your investigations show a possible solution to that?
I can't think of more ways so say yes. It is just a matter of making it practical.

It all about which ALSA drivers are loaded/used - and how mpd is set up.
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Old 26th February 2014, 12:21 PM   #183
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Hello people, i'm developing an acoustic analyzer unit based on the BBB with the "Audio Cape", my intention is to replace this cape for a better audio quality. I'm struggling very hard to make ASoC to recognize my custom ADC as a soundcard (i'm currently working with the ti pcm1803a which doesn't have I2C control interface).

Looking forward for reading your progress with the BBB!
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Old 26th February 2014, 06:24 PM   #184
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Originally Posted by Russ White View Post
I can't think of more ways so say yes. It is just a matter of making it practical.

It all about which ALSA drivers are loaded/used - and how mpd is set up.
Thanks Russ. I assume that once the drivers are developed the solution will aply to more than just MPD? I use Squeezelite, to date, with USM DACs, as long as the drivers are loaded SL seems happy.
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Old 26th February 2014, 07:06 PM   #185
mjock3 is offline mjock3  United States
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@ syklab see post #54 of this thread there is some good info on element 14 on this.

Mark
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Old 26th February 2014, 07:37 PM   #186
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Quote:
Originally Posted by syklab View Post
I just got a BBB delivered yesterday and have been looking around on how to get I2S output from it, I haven't seen any new release from Volumio which might address the I2s payback for BBB yet, is it coming soon? Any hint from expert?
Its already possible to get music out of the BBB via I2S, I have had it running using the latest Debian Wheezy OS using FFMPEG. Also had music using Volumio tho I did have a problem with distortion on one channel. However there are issues with resampling to 48khz (and possibly other issues) which need addressing before its a fully working solution. As above a few people looking into it on different forums. Rune Audio also looking to get a new relase with I2S support but I don't think they will have the 48khz issues sorted. I wish I could contribute but I am hitting the limits of my knowledge!

I also have a Raspberry Pi running fine via I2S but really want to get the BBB going - better platform or our needs.

Puting my hopes on Russ to get this one sorted
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Old 27th February 2014, 11:23 AM   #187
miero is offline miero  Czech Republic
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BBB has 24.576MHz oscillator only. It allows to generate 48000Hz and its multiples. See the figure 45. in the BBB_SRM.pdf.

It seems that cape could add another oscillator for 44100Hz frequencies and route it to the same pin.

And switch between them via oscillator OutputEnable control pins.
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Old 27th February 2014, 12:54 PM   #188
tunasto is offline tunasto  Netherlands
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BBB is supposed to play 32bit/128khz over SPDIF.
Formula for oscilator freq is:

32bit * 2 channel * 2(slots) = 128

128 * 192khz = 24.576 Mhz

For I2s, there is no 2 slots only one, so formula is 64 * fs, which is 32bit/384khz with 24Mhz oscilator


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Denis
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Old 27th February 2014, 07:04 PM   #189
glt is offline glt  United States
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Quote:
Originally Posted by miero View Post
BBB has 24.576MHz oscillator only. It allows to generate 48000Hz and its multiples. See the figure 45. in the BBB_SRM.pdf.

It seems that cape could add another oscillator for 44100Hz frequencies and route it to the same pin.

And switch between them via oscillator OutputEnable control pins.
It seems that way. Also the processor only has two integer coefficients for clock division, so there is no way to generate the 44.1K clocks from the on-board clocks.
A cape with two clocks, clean power supplies and connectors for I2S would be a good starting point... (and the drivers that would take advantage of these clocks)
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Last edited by glt; 27th February 2014 at 07:07 PM.
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Old 27th February 2014, 08:01 PM   #190
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Thanks, that greatly improves my understanding of the issue.

Looking at the RaspberryPi I see 2 oscillators with frequencies 25.000 and 19.20 stamped on them. So, unless these aren't the actual frequencies, how would that be working?
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