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Surround decoder for encoded digital audio (AC3, DTS, AAC) with Beagle Bone Black
Surround decoder for encoded digital audio (AC3, DTS, AAC) with Beagle Bone Black
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Old 20th March 2019, 07:06 PM   #11
janho12345 is offline janho12345  Germany
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And here it comes, another stupid question.

In the schematic there is one i2s data line to the dac.
Why not 4 data lines? The BBB is able to output 4 i2s data.
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Old 20th March 2019, 07:24 PM   #12
mushroommunk is offline mushroommunk  United States
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And what is the EEPROM used for? Doesn't BeagleBone have plenty of storage?

I know I know, you're updating the project page, patience people.
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Old 20th March 2019, 08:46 PM   #13
halfgaar is offline halfgaar  Netherlands
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Quote:
So, basically the setup is that you receive S/PDIF and feed into a DIR9001 to get I2S. That signal is fed into the Beagle where it is decoded (AC3/DTS) and the result is output to a 8-ch DAC.
Ffmpeg autodetects the codec, so AAC should also work. Unfortunately, DTS True HD and Dolby Atmos and stuff require more bandwidth than s/pdif offers, so that's off the table (although I smell a new project coming, if not for ******** HDCP ).

Quote:
You use I2C to select what DAC to output to. Neat!
This is pretty common in DAC world. Sound cards do it internally to control volume, muting, anti-pop, sample rate, etc. Because of SOCs (system on a chip) ARM systems emerging, ALSA designed ALSA-SOC that allows direct interfacing of DACs through IS+IC, without drivers having to re-code the same DAC in slightly different ways.

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I think that you would do the community a great service if you were to amend the instructions for the software so that those of us who do not speak Linux with complete fluency could follow
I made the designs public because I indeed want to help people out, but I did realize it unfortunately isn't so plug-and-play. For instance, the ALSA-SOC layer imposes restrictions that the hardware doesn't have, so I hacked a driver that will never be accepted for inclusion in the kernel.

At this point I think knowing how to cross-compile software and drivers is somewhat unavoidable. I have an image file of the EMMC with the software installed that anybody is welcome to use, but that requires my exact schematic.

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And here it comes, another stupid question.
I think think this project invokes a lot of questions, it's fine . I also invite you to look at the git history on Github of both the schematic and code. I like explaining the 'why' in git history, and what I learn.

Quote:
In the schematic there is one i2s data line to the dac.
Why not 4 data lines? The BBB is able to output 4 i2s data.
The pins can only be muxed in certain ways, and there was no way I could use 4 data lines. I needed pins for two master clock in, frame clock in/out, bit clock in/out, data lines, etc.

It's a theoretical bummer, because I now use time multiplexing, and therefore need the 512 times clock recovery option on the DIR9001. That makes the maximum sample rate 48 kHz. I haven't been hit by it yet, but HD audio is off the table from the start (although I don't believe in HD distribution of audio).

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And what is the EEPROM used for? Doesn't BeagleBone have plenty of storage?
The beagle bone 'cape' manager scans a certain Ic port for autodetection of device ID for automatic driver loading and reading pin mux settings for checking compatibility with other cape boards.

Quote:
I know I know, you're updating the project page, patience people.
The original post was a year ago, so that shows how fast I am . I'm actually working on instructions for the cross compilation of ARM source; already quite some work.

Last edited by halfgaar; 20th March 2019 at 08:55 PM.
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