Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Software Dolby live encoding? (Read 10453 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Software Dolby live encoding?

Hi there,

I wonder if the following is possible:

If you have a soundcard that is connected digitally to an external Dolby Digital (or DTS) receiver but does lot support Dolby live encoding, couldn't you write a fake (software) windows driver for a virtual soundcard that encodes multi channel audio to Dolby Digital (or DTS) and sends this stream to the physical soundcard. The physical one then sends the signal via SPDIF to the external receiver in order to get digital multi-channel audio.

Is the above possible?

Software Dolby live encoding?

Reply #1 –
Quote from: bladecgn on
Hi there,

I wonder if the following is possible:

If you have a soundcard that is connected digitally to an external Dolby Digital (or DTS) receiver but does lot support Dolby live encoding, couldn't you write a fake (software) windows driver for a virtual soundcard that encodes multi channel audio to Dolby Digital (or DTS) and sends this stream to the physical soundcard. The physical one then sends the signal via SPDIF to the external receiver in order to get digital multi-channel audio.

Is the above possible?


Both Dolby and DTS encoding schemes are proprietary. One would have to either license the encoding technolgoy or purchase 3rd-party encoding hardware and/or software.

I'm not sure if you are speaking specifically of 'Dolby Live' or just Dolby realtime encoding in general, but in either case, a RT encoder won't come cheap. Examples include:

Dolby DP571 Encoder for about $5,600
OR...
get the Neyrinch SoundCode 5.1 Encoder Plug-In for Digidesign ProTools (?cost unknown?)
OR...
DIY (simulated surround from 2ch st.) - http://www.5dot1.com/articles/poor_mans_surround.html

But in the case that you describe, why not just use the multi-channel inputs that most-likely are present on you decoder.
I've seen plenty of high end post production houses use a generic Dolby decoder (eg the typical Sony surrond receiver/decoder that you can pick up at any major retail electronics chain). As for a RT encoder; you better be ready to pony up for the DP571, or the like!!!

Software Dolby live encoding?

Reply #2 –
Quote
As for a RT encoder; you better be ready to pony up for the DP571, or the like!!!

Oh yeah -- 'cause pro studio guys prefer expensive hardware over software which does the same if not better. LOL

I believe the X-Box does realtime AC3 (dolby digital) encoding (Does it really?). What the OP suggested shouldn't be too hard to build in theory. There's even an open source AC3 encoder available (ffmpeg, BeSweet) which doesn't have to be that good actually because the bitrate doesn't really matter (you could choose a high bitrate).

Though, first thing that comes to mind is: increased delay. The encoder needs to buffer up to around 1700 samples before being able to produce a coded AC3 frame + the time to actually encode it. On the decoder side you've a decoder delay of time-needed-to-decode-the-frame + 128 samples (half of the frame overlap). So, you'll experience a delay of at least 38 ms.

S

Software Dolby live encoding?

Reply #3 –
I thought AC3Filter did this? I thought people used it for getting 5.1 WMA into a form their DD/DTS amps can use?

Software Dolby live encoding?

Reply #4 –
Quote from: SebastianG on
I believe the X-Box does realtime AC3 (dolby digital) encoding (Does it really?).


Yes, it does, as well as some chipsets for Mainboards do, and it is Dolby Digital Live Encoding. This
is actually not the same as the Dolby Digital Consumer Encoder, or the professional one as realized
it the DP571.

Quote
There's even an open source AC3 encoder available (ffmpeg, BeSweet) which doesn't have to be that good actually because the bitrate doesn't really matter (you could choose a high bitrate).

These implementations sure miss some parts you won't find in the public documents, for good reason :-)
Although I agree that the developers did a good job, it is even multichannel now...

Quote
128 samples (half of the frame overlap). So, you'll experience a delay of at least 38 ms.

Half of the frame would be 768 samples/channel, actually the decoding delay is "time to receive
2/3 of the encoded frame + one block (256 samples /channel)", as far as I remember.

Cheers

Herwig

Software Dolby live encoding?

Reply #5 –
Quote from: mcbear on
Quote

128 samples (half of the frame overlap). So, you'll experience a delay of at least 38 ms.

Half of the frame would be 768 samples/channel, actually the decoding delay is "time to receive
2/3 of the encoded frame + one block (256 samples /channel)", as far as I remember.

Sorry, I meant "half of the MDCT's overlap" which is 128 samples. I was just trying to give a lower bound on the encoder-decoder delay. A frame contains 6 audio blocks (each 256 spectral coefficients). And yes, a decoder could start decoding the blocks before it fully received the frame.

Let's recap: You'll have 256 samples/chan of filterbank-delay (encoder+decoder) due to the TDAC. Apart from the analysis filterbank on the encoder side an encoder (most likely, doesn't it?) buffers at least 1536 samples/chan before producing & transmitting the coded frame. Let's assume encoding & transmission is lightning fast (it isn't) and the decoder is a quick one which starts decoding the data ASAP and therefore introduces another delay of at least 1 block (256 samples).
=> 8*256 samples/chan = 43 ms * 48 kHz (at least)

...which micht be unacceptable for certain applications.


S.