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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 7th March 2018, 07:29 PM   #1
halfgaar is offline halfgaar  Netherlands
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Default Surround decoder for encoded digital audio (AC3, DTS, AAC) with Beagle Bone Black

(Almost) finished project. Digital 7.1 audio decoder for DTS, AC3, AAC, and all that FFmpeg will decode and fits on a TOSLINK bandwidth.

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Sources and design (all GPL v2):

Project page, to be expanded
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Old 7th March 2018, 07:30 PM   #2
Juergen Knoop is offline Juergen Knoop  Germany
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great!
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Old 19th March 2019, 05:04 PM   #3
mushroommunk is offline mushroommunk  United States
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I'm just considering this myself as well, running this between my tv and a soundbar I want to build.

One question, any particular reason you didn't use the pocketbeagle? From what I can tell it's cheaper but still has access to the MCASP on the chip for in/out and is the same processor.
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Old 19th March 2019, 07:08 PM   #4
halfgaar is offline halfgaar  Netherlands
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I wasn't aware of the Pocket Beagle. Did it even exist at the time? But for me it doesn't matter, because I had ample space.

I'd like to add a note BTW, that this solution doesn't work well for devices connected with HDMI to your TV. At least not my Panasonic Vierra. Audio passthrough just doesn't work, and all connected devices just output stereo PCM. It seems to be a DRM/HDCP thing; the TV tells the source device what to output in.

I'm still confused about it though, because this states that all the TVs they tested can pass through.
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Old 19th March 2019, 07:38 PM   #5
mushroommunk is offline mushroommunk  United States
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Pocketbeagle came out late 2017 I believe. For me I'm just considering cost, $25 vs $50.

I thankfully don't have any hdmi sources connected to the TV. Well, a blu-ray player we never use as we go to the theater. I mostly want it so I can get an actual center channel. My girlfriend loves her soap operas and watches them on the Hulu tv app, so this will work great. Can output from the app through toslink, pull out the L/C/R and EQ from there.

Do you have any notes on resource utilization? I'd imagine it's quite lite.
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Old 19th March 2019, 08:20 PM   #6
halfgaar is offline halfgaar  Netherlands
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Given the finishes I did to it, $25 wouldn't have made difference

I don't fully recall the resource use, but I think it was about 30% or so (if memory serves, that is about the same as playing an MP3 on a Pentium 100). I configured it to run my decoder software with real-time scheduling, because it was sensitive to skips. I never really understood why, because the whole audio system was driven by an external clock, so all output and input should have been impossible to desynchronize.
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Old 19th March 2019, 11:09 PM   #7
janho12345 is offline janho12345  Germany
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This sounds great, and I want to know more!

On the project page you write that the S/PDIF signal is received by a DIR9001. I don’t quite understand that, as I thought the DIR9001 can just receive 2 Channel PCM of S/PDIF and gives out i2s.
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Old 20th March 2019, 07:22 AM   #8
kipphebel3 is offline kipphebel3  Aland Islands
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Very Nice! Can you please add schematics in PDF-format on the project page? So that readers can get an overview picture without installing Eagle?

So, you receive the signal, process it in the BeagleBone and then output the individual channels through their DACs?
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Old 20th March 2019, 03:45 PM   #9
halfgaar is offline halfgaar  Netherlands
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Quote:
This sounds great, and I want to know more!

On the project page you write that the S/PDIF signal is received by a DIR9001. I donít quite understand that, as I thought the DIR9001 can just receive 2 Channel PCM of S/PDIF and gives out i2s.
The DIR9001 has an AUDIO output pin, which is high or low depending on whether it sees PCM or encoded data.

Quote:
Very Nice! Can you please add schematics in PDF-format on the project page? So that readers can get an overview picture without installing Eagle?
I could, but the project page needs a lot more that I haven't gotten around to yet. Allow me some time, and I'll see if I can manage something.

Quote:
So, you receive the signal, process it in the BeagleBone and then output the individual channels through their DACs?
In a nutshell, yes. Depending on the aforementioned AUDIO pin, I just write bytes to the sound device, or use ffmpeg to decode it.
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Old 20th March 2019, 06:29 PM   #10
kipphebel3 is offline kipphebel3  Aland Islands
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Quote:
Allow me some time, and I'll see if I can manage something
Sorted it. Latest version of KiCad can import Eagle directly. A schematic says more than 1k words

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.

This answers the question I had earlier. I guess I could use your design and have digital outputs instead.

You use I2C to select what DAC to output to. Neat!

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

PDF Schematic attached
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File Type: pdf Schematic.pdf (279.1 KB, 14 views)
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