[Arm-netbook] A10 and all things audio

[Mark Wilczynski]

> Date: Fri, 13 Jul 2012 11:20:02 +0900
> From: lundman at lundman.net
> To: arm-netbook at lists.phcomp.co.uk
> Subject: [Arm-netbook] A10 and all things audio
> 
> 
> 
> Mele A2000 / Allwinner A10 Android 4 ICS, Mele image.
> 
> 
> After fixing the networking and video playback, I took my mele home to test 
> as a mediaplayer.
> 
> Alas, the sound has some issues. I am mostly interested in audio 
> pass-through, ie, send the audio stream to the avr/amp or tv directly. More 
> than 2 channels generally. Thus, I did not try the RCA plugs. Since we are 
> not talking about decoding audio, just pass-through, the license changes 
> regarding DTS does not apply.
> 

Welcome to the mailing list lundman!
As we discussed on IRC, the a10 seems to have some timing/clock problems when it comes to video.  Maybe audio suffers from the same problem and your AVR has trouble locking-in on the sampling frequency of the signal.  Did you test with stock Mele android 2.x image?  Back when I still had my a10 tablet running android 2.x, it didn't have any audio issues on my TV (stereo PCM only) except for a/v sync problems on some files.  Never tried hooking the tablet to my AVR.  HDMI only supports a very small subset of audio frequencies - I always stick to 48 Khz.
I just remembered a discussion I had with another list member about the video timing issues here:
http://permalink.gmane.org/gmane.comp.hardware.netbook.arm/2420

Maybe adjusting that master clock would be useful?  Maybe there is a similar clock for audio somewhere.
I'm pretty sure nobody has ever gotten audio pass-through to work on any a10 device.  But it should not be difficult to pass standard ac3/dts inside the PCM signal (assuming you can first fix the problems you're having with PCM).  You just need to wrap the compressed audio frames in some spdif headers(8 bytes) and pad the frames to cover the same number of PCM samples that are inside the compressed data.  For example - a AC3 frame will have 1536 samples (also 1536 bytes at 384 kbps).  So you need to make sure it's transmitted over the 6144 bytes that make up 1536 stereo-16-bit PCM samples.  8 byte header, 1536 byte AC3 frame, 4600 bytes zero padding.  If I remember correctly you also need to byteswap the payload following the header so it's big-endian.  You would need to feed that directly to the audio hardware as if it was plain PCM data - not sure if any of the android audio players can play raw pcm?

 		 	   		  
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