Downmixing with custom (DPII) matrix on Mac OS X? matrix, completely, anybody, custom

andy

Does anybody know of a (free-ish?) tool for Mac OS X that lets you specify a custom downmix matrix from 6 mono sources into a 1 stereo output?

I am trying to transcode Dolby Digital AC3 5.1 to Dolby Pro Logic II on a Mac, not necessarily realtime (since this is for DVD ripping anyway). I know mAC3dec can downmix to a fixed Dolby Pro Logic (non-II) stereo file, but that is not enough. I know how to extract the AC3 track from a DVD, and how to split it into 6 mono sources, but am completely lost at how to downmix it to a stereo file using a custom downmix matrix, such as the ones specified in this thread?

Yes, not the first time I ask this, but thought about giving it a dedicated thread, just in case someone missed it.


Originally Posted by elmimmoDoes anybody know of a (free-ish?) tool for Mac OS X that lets you specify a custom downmix matrix from 6 mono sources into a 1 stereo output?

I am trying to transcode Dolby Digital AC3 5.1 to Dolby Pro Logic II on a Mac, not necessarily realtime (since this is for DVD ripping anyway). I know mAC3dec can downmix to a fixed Dolby Pro Logic (non-II) stereo file, but that is not enough. I know how to extract the AC3 track from a DVD, and how to split it into 6 mono sources, but am completely lost at how to downmix it to a stereo file using a custom downmix matrix, such as the ones specified in this thread?

Yes, not the first time I ask this, but thought about giving it a dedicated thread, just in case someone missed it.

The downmix matrix (s) that are mentioned sound okay, but are not true DPLII. It involves very precise mixing to get a good balance of sound. You can absolutly hear the difference when comparing these matrix to the Surcode DPLII encoder that has just been released. I recommend you or anyone to go out and purchase it if you want proper DPLII mixing.


Originally Posted by specise_8472I recommend you or anyone to go out and purchase it [Surcode DPLII encoder] if you want proper DPLII mixing.

Did you just go and recommend a $495 software for home DVD ripping activities or what? ^_-

Anyhow, back to the point. How do I check in OS X how okey those download matrix are? How do I downmix to stereo using custom matrix in OS X?


Originally Posted by specise_8472The downmix matrix (s) that are mentioned sound okay, but are not true DPLII. It involves very precise mixing to get a good balance of sound. You can absolutly hear the difference when comparing these matrix to the Surcode DPLII encoder that has just been released. I recommend you or anyone to go out and purchase it if you want proper DPLII mixing.

Actually it seems that these equations work properly
showthread.php?s=amp;threadid=57988
The incorect decoding is related often to the fact, that many
software decoders simply do not work as they should.


Originally Posted by 3dsnarActually it seems that these equations work properly
showthread.php?s=amp;threadid=57988
The incorect decoding is related often to the fact, that many
software decoders simply do not work as they should.

I know it sounds good, but I find it hard to beleive that it is true DPLII as true mix requires phase shifted 90 degree rear channels. This is from all the reading I have done and from the Patents. Actually from one of the latest Patents, it is revealed that DPLII is based around the Quad QS format.

the 90° phase shift IMO is nonsens, because 90° phase shift is only valid for a single frequency.
with other frequencies the phase shift will deviate.


Originally Posted by scharfis_brainthe 90° phase shift IMO is nonsens, because 90° phase shift is only valid for a single frequency.
with other frequencies the phase shift will deviate.

Then you had better tell Dolby Laboratories that they have got it wrong all these years.

the problem is that I can read everywhere, that DPL should be +90° and -90° mixing. but how does one establish a filter of a constant 90° phase shift through the whole audible spectrum?

IMO this +90°/-90° shifter thing is nothing than a very small delay, that is followed by a 0°/180° shifted encoding...

But you may proove me wrong with patent papers and technical papers for DPL(2) or an explantation of that issue


Originally Posted by scharfis_brainthe problem is that I can read everywhere, that DPL should be +90° and -90° mixing. but how does one establish a filter of a constant 90° phase shift through the whole audible spectrum?

IMO this +90°/-90° shifter thing is nothing than a very small delay, that is followed by a 0°/180° shifted encoding...

But you may proove me wrong with patent papers and technical papers for DPL(2) or an explantation of that issue

You are right. 90degree phase shift is the Hilbert Transform. Plenty on the net a Google search will turn up

But a poor mans DPL is as you say 180 with delay..

Try this for an excellent explanation of this implementation.

features/so...urround_03.htm

As you can see, DPLII encoding still involves more than just mixing the signals with a set of co-efficients.


Originally Posted by scharfis_brainthe problem is that I can read everywhere, that DPL should be +90° and -90° mixing. but how does one establish a filter of a constant 90° phase shift through the whole audible spectrum?

IMO this +90°/-90° shifter thing is nothing than a very small delay, that is followed by a 0°/180° shifted encoding...

But you may proove me wrong with patent papers and technical papers for DPL(2) or an explantation of that issue

Also another good use of this is take the Stereo signal, Invert it (NEG), delay it (~20 samples for 44.1), swap channels, then mix back into the original signal.

This creates a reasonably good crosstalk canceller.

Also another good use of this is take the Stereo signal, Invert it (NEG), delay it (~20 samples for 44.1), swap channels, then mix back into the original signal.

This creates a reasonably good crosstalk canceller.

Such a thing my dad built about 25 years ago. It was a small little box with a linear control over Mono...Stereo...Mono-Cancellation.

THis is called quot;Basisbreitenreglerquot; in German. And was used to make sound the Stereo image wider.

Er#8230; yeah, nice chit-chat. ^_-

What about regarding those stereo downmixing tools for Mac OS X, or something Linux-ish and command-line that might compile on it?