SPDIF recording format

[hypercube]

My soundcard doesn't have any SPIDF input connector. So I can't test my idea.
anybody can explain to me how SPDIF stream are recorded on PC ?

if you play a AUDIO DTS CD and record it with your PC via SPDIF, what is the recording result ? a WAV with DTS inside ?

if you play a LaserDisc with AC3,does AC3 inside WAV ?

is it possible to rip the stream in IEC60958/IEC61937 format ?

[daphy]

Salut Hypercube,

nice to see you back, it´s been a long long time since you were here on this board :(

I can´t answer your question exactly but I did an interesting test:

I recorded a DTSWAV CD digitally (SPIDF) with an old DAT Recorder (which only supports 2.0 PCM streams.

The result was a DTS DAT recording 5.1.
-> so I´ll guess a PC input SPIDF should behave the same way :rolleyes:

[hypercube]

salut daphy,

>nice to see you back, it´s been a long long time since you were here on this board
yes, I don't have enough time to do all I want to do :D For instance, I'm making 5.1 muzic. It's amazing !

If I have enough time, I will implement MP2 Multichannel decoding in Hypercube Transcoder, because MP2 Multichannel is obsolete.

back to this thread: did you ever record via SPDIF ?

[daphy]

it´s a pritty long time ago I connected a DAT player via SPIDF (or coaxial) with the digital input of my former sound card - AFAIR(ember) :p it worked with the program I chosed to record.
Maybe I should do a test but it´s (as always) a question of time :(
My latest card, an audigy4 pro has both connections (coaxial and SPIDF) on the extra board, so it should be possible to manage this without to much effort - we will see :rolleyes:

If I have enough time, I will implement MP2 Multichannel decoding in Hypercube Transcoder, because MP2 Multichannel is obsolete.
BTW: you want to implemet something you self called obsolete :confused:

[hypercube]

>you want to implemet something you self called obsolete
yup. encoding is obsolete now. :)

so how to retreive 5.1 PCM from previous encoding ? :-)

[mic]

SPDIF is a 2 channel digital transport to carry one or two channels of audio. But it also can carry DD AC3 and such, because digitally, it's just like any other data stream.

PC audio hardware can pass it through to software, or handle it direct, & most with spdif input will do stereo as this doesn't require decoding. When you use multi-channel, you usually have the option of pass through to software decoders working with the drivers, or pass through to spdif out to connect with external hardware like stereos.

Hardware like the Soundblaster Audigy line have hardware decoding I believe, though it's best available using their software player to record [the audigy line can tap into the feeds before they hit the speakers]. Most I think are like Soundblaster in limiting your abilities to grab the digital signal intact.

There are a few cards that can handle it, passing the spdif stream without going through the DAC(s), and then it's possible to record that signal. I went through notes and posted one of the cards I thought worked this way a while back - think it was Turtle Beach Catalina - and there's a couple of good threads here from 2003 I think. I know the steps to modify the results into a legal ac3 were posted -- I don't think it went into DTS so would have to work on that part.

If I remember correctly, from a cable box etc. the multichannel audio was sent as frames to keep sync with the video, and recorded with the extra dead time between pulses -- that had to be removed. Don't know how it would work with other sources, & I think a separate thread dealt with Laserdisc -- don't think it was possible there.

Again, hope that this might help :)

Edit: adding on...
If your card has a CD digital in (usually on card board itself), this will often work as co-ax spdif in. If you start putting things together, many sources apparently that have spdif co-ax out provide a sub-spec signal level. And if you or someone you know is so inclined, there is some good info on various spdif homemade covertors at driverheaven.net

[Rockaria]

I don't have any experiences with the 'bit-accurate' sound cards bypassing the capture device and performing the live DD decoding/capturing with exact bit rate, but have some experience capturing the soundstorm-encoded(or raw passthroughed) ac3 streams through ttl-connected spdif-in and the soundstorm capture device.

It seemed to me the capture device is enforcing the spdif-in stream to be 44.1k pcm stereo. The graphedit only allows to save the capture stream to 44.1k wave through wavedest ds filter. Soundstorm is known to transmit 48khz pcm or ac3 spdif signal.

Below are the threads related.

spdif capture using professional cards (http://forum.doom9.org/showthread.php?s=&postid=338286#post338286)
my soundstorm spdif-in capture test (http://forum.doom9.org/showthread.php?p=645320#post645320)

[johnman]

I have experimented a little with digital recording a long time ago, and IIRC some cards can record the input bitidentical and some cant, and sometimes it depends on the sampling rate.

My old card worked on 48 khz so it could only record the stream bitidentical if it was on 48khz. All other samplerates would be resampled to 48 khz. Some soundcards can record bit-identical @ all usual samplerates, but i have never had one of those, so i dont know to much about them. I believe one of those expensive terratec cards can do this (i believe the teratec universe ??).

There is also i minor issue with recording from minidisc and some other devices. It had a bit which caused some soundcards to not record the stream. I believe it was something like SCMS.

I think when you record a stream in a true bitidentical way, you get just the raw sample data without any wav header. So if its a ac3 stream, you get ac3, and the same for dts. But this also might depend on the software you use. But im just guessing here :).

[hypercube]

thanks for this informations. I wanted some SPDIF rip because I discover that AC3 in AUDIO CD (encapsulated in a WAV) are in the same format as SPDIF.
My idea is to try to make AUDIO CD with other bitstream: MP2 for example.
just for the fun !
And you know what ? it does not work. :p
May be my code is buggy, but I'm pretty sure that it was impossible, finally.

[Rockaria]

Other than MP2! :)
If the purpose is to write music on a CD playable on a dvd player, mp2 is already serving in vcd and svcd formats..
But certainly these formats are not audio cd which requires 44.1khz 16bit 2ch wav written in 1411kbps to be decoded.

Maybe still it's possible because the dvd player has the mp2 decoder(for the vcd and svcd format)?
But decent DVPs cost around $40~50 these days..