Re: OT: seeking simple digital interface which can pass AC-3 _input_
Re: OT: seeking simple digital interface which can pass AC-3 _input_
- Subject: Re: OT: seeking simple digital interface which can pass AC-3 _input_
- From: Stephen Davis <email@hidden>
- Date: Thu, 30 Aug 2007 12:40:19 -0700
Yep, to test I use "afrecord -f AIFF -d BEI16" and then look at the
resulting file. In my live test, I ask the input side of the output
unit for 16-bit big-endian data.
When I look at the resulting file for AC-3 data, the first part of
the SPDIF AC-3 sync preamble is 0xF872 - 0x4E20 (wrong, it's supposed
to be 0x4E1F) but the rest of the data works out -- type = AC-3,
length = 1536 bytes, etc.. Then, I find the AC-3 header 0x0B77 and
confirm that the bit rate, sample rate, etc. are valid but the
following CRC check fails. I didn't keep looking into it after that.
stephen
On Aug 30, 2007, at 11:51 AM, Jeff Moore wrote:
When you are testing the data you are capturing, have you checked
for endianness? Some devices will bring the data in little endian,
some will bring it in big-endian. It should be indicated by the
format flags in the ASBD for the SPDIF stream.
On Aug 30, 2007, at 11:41 AM, Stephen Davis wrote:
Does anyone here have any recommendations for a simple s/pdif
digital interface (USB or FW) that can accept a digital bitstream
as input and *not* mess up the data? I have a MotU Traveler which
I love but it specifically states that it will not pass AC-3/DTS
data properly and I'm fine with that so I picked up an M-Audio
Transit USB in the hopes that it would but it doesn't either. The
sync header and some of the data make it through but liba52 gets
CRC errors on every packet. I've verified that the same code
works on a MacBook Pro with its built-in optical in. Maybe the
Transit USB *should* work but I need to configure the device
differently???
I've searched around but have yet to find anyone specifically
claiming that digital bitstream input will work properly on their
device. The built-in optical ins on the Macs all work but this is
for an old PPC mini that doesn't have one.
Apologies for the off-topic post but figured some of the folks
here probably know...
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