Guide: 2- to 5-channel upmix using Dolby Pro Logic II

[PDU]

Originally posted by ursamtl
An alternative would be to use the Spatdecode VST in a bidule. Spatdecode appears to produce only Pro Logic I output, but for 2-channel music, all DPLII does is add something called a "Panorama" control, which in reality simply sends some of the front channel to the back to give the illusion of "wrapping the soundfield around the sides of the listener." This also gives the illusion of stereo surrounds but in reality, the actual surround material is mono.

Anyway, just hook Spatdecode up to a 6-channel File Recorded leaving the fourth channel blank (for the empty LFE) and it should work.

Regards,
Steve.

Hi Steve,
Since I'm pretty new to bidule, I would appreciate if you could explain how to make the File Recorder start recording when play is activated on a 2 ch File Player. Oh, and another question. What output connectors on the Spatdecode VST produce which surround channel?

Spatdecode out 1 = ?
Spatdecode out 2 = ?
Spatdecode out 3 = ?
Spatdecode out 4 = ?
Spatdecode out 5 = ?

Cheers,
Peter

[ursamtl]

Originally posted by PDU
Hi Steve,
Since I'm pretty new to bidule, I would appreciate if you could explain how to make the File Recorder start recording when play is activated on a 2 ch File Player. Oh, and another question. What output connectors on the Spatdecode VST produce which surround channel?

Spatdecode out 1 = ?
Spatdecode out 2 = ?
Spatdecode out 3 = ?
Spatdecode out 4 = ?
Spatdecode out 5 = ?

Cheers,
Peter

Hi Peter,

Here`s the procedure for automating the recording so the starting times are aligned:[list=1][*]Check the "Toggles signal processing" icon (6th icon from top left corner). If the small square in the upper right corner of the icon is green (for "on"), click on it to toggle the square to red (for "off").[*]Click on the Tools menu and choose Parameters.[*]In the Parameters dialog box, expand the Audio file Player in the left Source pane and select Playing. [*]Expand the Audio file Recorder in the right Target pane and select Recording. [*]Click the Link button and see that the link is listed in the bottom pane[*]Click X at top right of screen to close Parameters dialog box.[*]Providing you're not planning to monitor your playback in bidule, go to the Edit menu and make sure the Offline Processing menu item has a check mark beside it. This uses as much of PC's processing power as possible to complete the conversion as fast as possible. Without this, the file is converted at playback speed; that is, a 5-minute song would take 5 minutes to write the file.[*]Double-click on the Audio file Recorder object to open its dialog box.[*]Set your bit depth (16, 24, or 32 bits).[*]Click the button on the right with three periods. This opens a dialog box for you to name and save your 6-channel file (although the dialog box title is "Select a file"). When you close this, do not click the Start button.[*]Double-click on the Audio file Player object to open its dialog box.[*]Click on the button at the lower right corner of the Audio file Player dialog box to Open your source audio file. Navigate to the folder containing your file, select the file, then click OK.[*]Click the Play button on the Audio file Player. Notice that the Start button in the Audio File Recorder changes to Stop, but the Elapsed time counter remains at 00:00:00.[*]Click the "Toggles signal processing" icon (6th icon from top left corner) to toggle the small square to green (for "on"). The Audio File Player starts playing the file at the same time as the File Recorder starts writing a file. Notice that in offline mode, the Elapsed time readout does not always increment smoothly. Instead, it jumps rapidly in chunks of several seconds, depending on your PC's power.[/list=1]As for Spatdecode's outputs, I'm not sure as I'm at work right now. I'll try to check it out and get back to you.

Steve.

[PDU]

Hi Steve,

Thanx a lot. Very detailed instructions. I think I'll be able to make this work. I do however have another question - hope you don't mind. Since my input file is 44.1 KHz but AC-3 files should be in 48KHz I would like to make some kind of samplerate conversion. Can this be done without installing any kind of additional VST plugins? If not, can you recommend a freeware plugin for this task? I guess I could always convert my sourcefile to 48KHz before loading it into bidule but it would be nice to do it "on-the-fly".

Cheers,
Peter

[joshbm]

I don't have Bidule up in running right in front of me, but I believe you are able to set the out file as 48 Khz by going to Preferences.

Regards,
Josh

[PDU]

Yes, I've tried that. Unfortunately it applies the "Mickey Mouse" effect to the resulting output (hope I make myself clear).

[ursamtl]

Probably the best freeware sample rate converter I've seen is Voxengo's R8Brain at http://www.voxengo.com/r8brain/. This is a bit of s slow program, but it produces good results.

By the way, I checked out SpatDecode and the channel layout is as I expected, F, R, C, sL, sR. Thus you could connect it the first three SpatDecode pins to the first three Audio File Recorder pins, leave the 4th Recorder pin unconnected, then connect the SpatDecode pins 4 and 5 to Audio File Recorder pins 5 & 6.

By the way, the surrounds are mono. They're both simply the L-R difference signal with sR feed inverted. This is as per Dolby's specs. By putting the surrounds out of phase, localizing specific sounds is more difficult.

Steve.

[joshbm]

@ursamtl

What about hp_ssrc.exe? I've been using that for my sample rate conversions, does R8Brain yield better results?

PS- The normal specs on an AC3 file is 24-bit, 48KHz... correct? Or do they use 32-bit float? What I am talking about is a normal NTSC DVD Movie, Dolby Digital 5.1 AC3 here.

Thanks!
Josh

[ursamtl]

Originally posted by joshbm
@ursamtl

What about hp_ssrc.exe? I've been using that for my sample rate conversions, does R8Brain yield better results?

PS- The normal specs on an AC3 file is 24-bit, 48KHz... correct? Or do they use 32-bit float? What I am talking about is a normal NTSC DVD Movie, Dolby Digital 5.1 AC3 here.

Thanks!
Josh

Yes, you're right. I forgot about ssrc (I don't know about the "hp_" prefix. I've never heard of it and Google turns up nothing). r8brain is better for those who like a GUI, but SSRC seems fine otherwise. I don't know if anyone has test data or anything otherwise scientific for a comparison of the two. I haven't done much work at all converting to 48kHz because my interest so far has been music. I do have some video footage with soundtracks I eventually plan to upmix to 5.1, so one of these days I'll have to get to the 48kHz stuff.

As per the AC3 bit depth, I'm not really sure. I've seen varying discussions on this but no solid answer. For sure 16-bit files should work on all playback devices but obviously 24- or 32-bit files will give better quality. From what I've read the difference between the latter two is virtually inaudible so if the software you're using only support 24-bit, don't sweat it. As a result, you don't really need dithering when reducing from 32 to 24 bits.

Steve.

[PDU]

Offline samplerate conversion is no problem. Both SSRC.EXE and R8Brain are part of my standard collection I was however hoping that it was possible to do the conversion inside bidule. Would make things a lot easier and would not affect the source file(s).

@Steve
Thanks for all your help and the pinout explanation for the Spatdecode VST. Speaking of Spatdecode isn't this really a Dolby Prologic decoder Exactly what does it do when the input file is not Dolby Surround encoded in the first place but just an ordinary stereofile?

Final question - at least for now
I need some guidelines for Soft Encode. I have encoded some files using the V.I. bidule. The resulting 6-track wav-file opens up nicely in Soft Encode. Some of the channels have to be rearranged for proper setup but that's not a problem. After encoding to 5.1 AC-3 files i have used Audio DVD Creator to make a DVD-Video disc for playback on my system (can't handle DVD-Audio or AC-3 files burned on an ISO disc like MPEG's). However there's no sound at all, just complete silence. If I play back the AC-3 files in Windows there's no problem. So maybe it's Audio DVD Creator that messes up the files - or I use some wrong settings in Soft Encode. Anyway, a "How to encode 5.1 AC-3 files with Soft Encode" guide would be really helpfull and highly appreciated.

Cheers,
Peter

EDIT:
It seems to be Audio DVD Creator that messes up the AC-3 files when creating it's output. Just extracted the AC-3 stream from the DVD-Video created with Audio DVD Creator and the extracted AC-3 file is only 2.0 - and it's completely silent when played back in Windows. Too bad

[ursamtl]

Originally posted by PDU
Offline samplerate conversion is no problem. Both SSRC.EXE and R8Brain are part of my standard collection I was however hoping that it was possible to do the conversion inside bidule. Would make things a lot easier and would not affect the source file(s).

Unfortunately, I know of no way in a bidule to convert the sample rate in real time.

@Steve
Thanks for all your help and the pinout explanation for the Spatdecode VST. Speaking of Spatdecode isn't this really a Dolby Prologic decoder Exactly what does it do when the input file is not Dolby Surround encoded in the first place but just an ordinary stereofile?

Glad I could be of help, Peter. Yes, Spatdecode does a kind of basic Pro Logic decoding. I haven't discussed it with the author, but I suspect it doesn't implement all the proprietary Dolby ProLogic processing on the surrounds, such as modified Dolby B noise reduction, a 7kHz low-pass filter, or steering technology, but then again, some of these may be more effective for marketing than for sound reproduction. The basic decoding circuit is there and could easily be duplicated in a bidule group. It consists of L and R channels passed through as is. The center is L+R with attenuation. Dolby specifies -3dB attenuation, although in my tests last evening SpatDecode's center was at -6dB. The surrounds are both L-R but the right surround has its signal inverted to reduce localization, as I explained in my previous message.

What will it do to an ordinary stereo file? Depending on how the source file was mixed, the surrounds will consist of mostly ambience. If the source had instruments, vocals, or any other sounds hard panned to the L or R channel, they will also appear in the rears. So, it will probably be somewhat effective in producing a sense of surround. If you do a search for "Hafler" in this forum, you'll find that I mentioned how I used to achieve this effect with speakers.

You mentioned that you've encoded some files using V.I. <as ursamtl gleefully dons his "shameless self-promotion" hat > It also takes the ambience information present when one subtracts L-R, but it distributes the ambience throughout the 360° soundfield using a combination of ambisonic and other formulas found around the net. The main difference is that some of the ambience is distributed to the front and some of the direct sound to the rear. The overall effect is the closest I've heard to the 5.1 mixes from DVDs I rent.

Final question - at least for now
I need some guidelines for Soft Encode. I have encoded some files using the V.I. bidule. The resulting 6-track wav-file opens up nicely in Soft Encode. Some of the channels have to be rearranged for proper setup but that's not a problem. After encoding to 5.1 AC-3 files i have used Audio DVD Creator to make a DVD-Video disc for playback on my system (can't handle DVD-Audio or AC-3 files burned on an ISO disc like MPEG's). However there's no sound at all, just complete silence. If I play back the AC-3 files in Windows there's no problem. So maybe it's Audio DVD Creator that messes up the files - or I use some wrong settings in Soft Encode. Anyway, a "How to encode 5.1 AC-3 files with Soft Encode" guide would be really helpfull and highly appreciated.

Cheers,
Peter

EDIT:
It seems to be Audio DVD Creator that messes up the AC-3 files when creating it's output. Just extracted the AC-3 stream from the DVD-Video created with Audio DVD Creator and the extracted AC-3 file is only 2.0 - and it's completely silent when played back in Windows. Too bad

You can usually get great results with the default SoftEncode settings, but if you want to know more, get ready to do a bit of reading. Check out the excellent thread here called GUIDE: How To Properly Encode Dolby Digital Audio (AC3). It contains a wealth of info on the settings you'll find in SoftEncode. You can also check its help file and information from the Dolby Technical Library. Yeah, reading might not be as fun as actually doing the stuff, but it's been my experience that you can gain a much more thorough appreciation of the whole surround process if you get some idea of what's going on.

Enjoy!

[PDU]

You mentioned that you've encoded some files using V.I. <as ursamtl gleefully dons his "shameless self-promotion" hat >

I think I missed that the thread was originally posted by you. Thank's for the V.I. bidule anyway

Yeah, reading might not be as fun as actually doing the stuff, but it's been my experience that you can gain a much more thorough appreciation of the whole surround process if you get some idea of what's going on.

You're right. I have a lot to learn and reading is what I'll be doing for a while.

Regarding V.I.
The files I have encoded so far (1 actually) worked like a charm as soon as I muxed the resulting AC-3 file with som DivX video. My MPEG4 enabled DVD player was happy - and I was happy (Damn Audio DVD Creator). However I noticed that the levels of the rear channels are higher than the front channels. This is actually "spottable" just by looking at the channels in Soft Encode - and by listening to the file. Is this intentional? I mean is the 6 channels generated by the V.I. bidule correct in regards to levels or is some kind of leveladjustment in Soft Encode necessary? Also the LFE track level seems very low.

Before I forget. I changed the pin connections in V.I. to the following:

V.I. 1 -> Rec 1
V.I. 2 -> Rec 3
V.I. 3 -> Rec 2
V.I. 4 -> Rec 6
V.I. 5 -> Rec 4
V.I. 6 -> Rec 5

By doing this the resulting 6-track wavefile can be opened in Soft Encode without rearringing the channel assignments at all.

Now gonna play with the Spatdecoder and Bidule. Have some MPA files (Dolby Surround encoded) that has to be converted to AC-3.

Cheers,
Peter

[ursamtl]

Originally posted by PDU
You're right. I have a lot to learn and reading is what I'll be doing for a while.

Reading is good, but experiment a bit too. This will give you a better understanding of what you're reading.

Originally posted by PDU
The files I have encoded so far (1 actually) worked like a charm as soon as I muxed the resulting AC-3 file with som DivX video. My MPEG4 enabled DVD player was happy - and I was happy (Damn Audio DVD Creator). However I noticed that the levels of the rear channels are higher than the front channels. This is actually "spottable" just by looking at the channels in Soft Encode - and by listening to the file. Is this intentional? I mean is the 6 channels generated by the V.I. bidule correct in regards to levels or is some kind of leveladjustment in Soft Encode necessary? Also the LFE track level seems very low.

Before I forget. I changed the pin connections in V.I. to the following:

V.I. 1 -> Rec 1
V.I. 2 -> Rec 3
V.I. 3 -> Rec 2
V.I. 4 -> Rec 6
V.I. 5 -> Rec 4
V.I. 6 -> Rec 5

By doing this the resulting 6-track wavefile can be opened in Soft Encode without rearringing the channel assignments at all.

Now gonna play with the Spatdecoder and Bidule. Have some MPA files (Dolby Surround encoded) that has to be converted to AC-3.

Cheers,
Peter

The pinout changes you describe will work with SoftEncode. The order I used in V.I is the ITU 5.1 spec, which is pretty much the standard these days. I'm curious about your surrounds being louder than your fronts. This happens to me on perhaps one song out of 20 and only because of the way the song is recorded. That's why I put the level controls on the outputs. Try backing off on the rear level to about 0.6 or 0.7 and see what that gives you. 0.7 corresponds to approx. -3dB which is often recommended for surround level attenuation. However, this comes from processing movies, which have their surround level boosted by 3dB to compensate for the size of most cinema rooms. For upmixing music, the attenuation is normally not necessary.

Yes, the LFE level is low. This shouldn't matter if your playback system has bass management. It will direct bass from the main channels to the subwoofer. Some pros insist that one should never use the LFE on music, whereas others do use it. I set the LFE channel in V.I below 60Hz, which moves it out of the way of bass management crossovers and still uses the channel to give that extra bit of oomph to bass note fundamentals and drum transients for music, and all the low-frequency effects in movie soundtracks. The wave may look really small and at a low volume in Softencode but on a decent playback system, it's all you need. The option is also available in V.I to shut the LFE channel off completely.

In the end, go with what works for you and enjoy it.
Steve.

[joshbm]

Originally posted by ursamtl
Yes, you're right. I forgot about ssrc (I don't know about the "hp_" prefix. I've never heard of it and Google turns up nothing). r8brain is better for those who like a GUI, but SSRC seems fine otherwise. I don't know if anyone has test data or anything otherwise scientific for a comparison of the two. I haven't done much work at all converting to 48kHz because my interest so far has been music. I do have some video footage with soundtracks I eventually plan to upmix to 5.1, so one of these days I'll have to get to the 48kHz stuff.

As per the AC3 bit depth, I'm not really sure. I've seen varying discussions on this but no solid answer. For sure 16-bit files should work on all playback devices but obviously 24- or 32-bit files will give better quality. From what I've read the difference between the latter two is virtually inaudible so if the software you're using only support 24-bit, don't sweat it. As a result, you don't really need dithering when reducing from 32 to 24 bits.

Steve.

Sorry I meant ssrc_hp.exe.


Josh

[joshbm]

Guide was updated

http://forum.doom9.org/showthread.php?s=&threadid=83384

Suggestions/Comments welcomed!

Regards,
Josh