Posting audio in surround sound

[Matt Pacini]

There isn't an "editing" category on the website, and this doesn't exactly fit into "production sound" so that's why I didn't post this over there...

 

OK, I'm upgrading to a nifty Behringer digital mixer/MIDI interface device, and it can record & mix in surround sound (what is it, 5+1?), and although I have 30+ years of audio & mixing experience, this is my first entry into recording/mixing in surround, and I'm really excited about doing it.

 

So, my questions are:

 

1. I'm editing in the computer, at this point only for video as a release format (probably just gonna be burning DVD's at first).

Am I opening a can of worms with this?

I mean, is it a breeze, or a nightmare of different formats, etc.,?

 

2. If I edit, and want to go to a film print (from a DI master), what's the best way to do that?

 

3. Do I need to create a separate 2 channel mix for non-surround enabled people, or do DVD players just automatically decode that from a surround signal?

 

Thanks!

Matt Pacini

[Guest Sean McVeigh]

1. I'm editing in the computer, at this point only for video as a release format (probably just gonna be burning DVD's at first). 

Am I opening a can of worms with this?

I mean, is it a breeze, or a nightmare of different formats, etc.,?

 

2. If I edit, and want to go to a film print (from a DI master), what's the best way to do that?

 

3. Do I need to create a separate 2 channel mix for non-surround enabled people, or do DVD players just automatically decode that from a surround signal?

<{POST_SNAPBACK}>

 

I just recently forrayed into 5.1 myself. It's pretty cool when you hear your first mix turn out right! Best of luck with your efforts!

 

I wouldn't consider myself an authority on the subject, but I'll offer some info. regarding your questions:

 

1. Formats are pretty standardized. Protools, digital performer, etc. support working in multi-channel formats. As does Steinberg Nuendo (what I was using prior to switching over to the Mac) -- there are some plug-ins out there to encode and decode pro-logic as well in case you want to mix down for VHS or similar. You'll probably be exporting AC3 or DTS in the end.. look into costs for encoders (I know DVD Studio Pro comes with an AC3 encoder on the Mac, and I am only familiar with one other on the PC). No worms really, just make sure you've got your monitors calibrated well for previewing your mixes.

 

2. The only place I checked out in terms of film prints would hand you 3 things when they finished. A silent negative, a sound track, and a merged positive print of the above. Dolby Digital is encoded between the perfs of a 35mm print I believe. You also usually print the optical sound track as well... if the 5.1 decoder ever loses sync, the sound processor falls back on the optical sound track.. you may have heard this happen in the theatre before. DTS is a bit different in that the soundtrack is actually stored on a few CDs in a computer, and the only thing (aside from the optical sound track) you print onto the film is a timecode that keeps the computer in sync. There was another format if I recall called SDDS which used the outside edge of the film to encode information, but from what I gather, this tends to wear out easier (could be wrong there). Be prepared to pay somewhere somewhere around $500/minute for film prints from D.I.

 

3. DVD video requires at least a linear PCM soundtrack or AC3 soundtrack be present on the disc. Most DVD players should downmix on the fly to some form of L+R track on the fly for the stereo audio outputs. (whether this is a prologic compatible stream or not, I don't know.. it may just be a mix of L+Ls and R+Rs).

 

For more information on surround track formats for film, check out:

Howstuffworks.com Movie Sound page

[Matt Pacini]

Thanks Sean.

 

I guess my biggest question is, what exactly do I need to do to get both stereo and surround onto a DVD?

 

I'm talking about posting the film completely at home, from start to finish (to DVD, that is, not film prints... maybe later).

 

Do all DVD decks "sense" the surround audio, and build a stereo output from that if the user isn't using surround, or do I need to have both on the DVD?

And do all the hardware/software surround options deal with whatever format the DVD spec needs by default?

 

Not sure how to do all that...

 

Matt Pacini

[Alvin Pingol]

Do all DVD decks "sense" the surround audio, and build a stereo output from that if the user isn't using surround, or do I need to have both on the DVD?

<{POST_SNAPBACK}>

 

I've played with DVD's that have both a 5.1 mix and a stereo (2 channel) AC-3 mix on my trashy Apex DVD player. When I toggle between the two audio tracks, they both play in stereo through my non-surround-sound audio setup. If my trashy Apex can downmix the 5.1 into a 2 channel stereo mix, I'd think other players would be able to, as well.

 

(Note, however, that the 5.1 mix did not sound as good as the 2-channel mix; it lacked the high frequencies, so I set it back to 2-channel mix, which sounded great in comparison.)

[Annie Wengenroth]

I recently took a class in Surround Sound mixing (we covered some mastering as well). We used a program called A-pack to lay out each channel from the bounced mix session, into a format that would "read" them the way they were in the session. Then we built the DVD in DVD Studio Pro, which is where we added the stereo mix.

 

I guess you *could* just have your 5.1 mix become your stereo mix, but my professor had us create a separate stereo mix of our project because otherwise, everything tends to get sort of "squished". With 5.1 Surround, you've got a lot more space to play with, literally. In stereo, you definitely have to handle it differently. Those ricocheting gunshots might sound really cool in surround, but in stereo, it could be very jarring. Also, Mr. Pingol was right about the frequencies.

 

Tomlinson Hollman (I hope I didn't butcher the name...) wrote a Focal Press book called "5.1 Surround: Up and Running". It's a worthwhile read if you want to learn more about creating 5.1 music or soundtracks.

[Guest Sean McVeigh]

I guess my biggest question is, what exactly do I need to do to get both stereo and surround onto a DVD?

....

Do all DVD decks "sense" the surround audio, and build a stereo output from that if the user isn't using surround, or do I need to have both on the DVD?

And do all the hardware/software surround options deal with whatever format the DVD spec needs by default?

<{POST_SNAPBACK}>

 

Again, I'm not an expert, but being an engineer by trade, I thoroughly read up on these subjects...

 

The DVD Video standard says that the disc can have multiple audio tracks in either AC3 or LPCM (Linear-PCM -- uncompressed), or where supported, DTS and MPEG-Audio. If the disc contains only one track, it MUST be one of either LPCM or AC3.

AC3 can contain any number of channels, the most popular being 5+1 and 1+1 (for plain stereo), and in fact, I've had to compress to AC3 1+1 recently on a project where the combined video bitrate plus LPCM bitrate was above the upper limit for the DVD standard (9.8MBps if I recall).

 

Anyhow.. to answer your question about whether players will automatically detect if it is surround or not -- yes, they will know what format the audio appears on the disc as (it's in either the program stream or in the audio frame headers). And in fact, ALL players should be capable of doing this, as the standard may allow for a disc solely with an AC3 5.1 track. Exactly HOW they accomplish this downmix is probably not specified though... so inconsitencies may result.

 

As someone else mentioned, if you have encoded to 5.1 surround, your DVD player will downmix for your stereo outputs, but the quality may not be as good as if you manually did the mix yourself and dropped it on the disc as a second audio track.

Through your DVD menus (or I guess, by just hitting the change-audio-track button on the remote), the viewer should be able to pick which one they want... and I might be mistaken here, but I think some DVD players will pick the correct soundtrack to play based on how they are configured (in the DVD player's menu itself, you can probably indicate that you want stereo by default.. probably not supported everywhere though.. just a speculation :)

 

As for what route to take.. if I were doing it.. I'd get a 5.1 mix perfected, and then encode it to AC3 5.1 (using A.Pack for example, which comes with DVD Studio Pro. there are others of course -- softencode comes to mind for the PC). After putting the AC3 mix aside, I'd drop the LFE channel (.1) from the 5.1 mix, manually mix the center channel into the Left and Right and then mix some elements from Left-Surround and Right-Surround into Left and Right as appropriate. Basically, a manual remix. (you probably want to avoid using LPCM for your audio tracks.. the required bandwidth is probably better allocated to increasing the picture quality).

 

With respect to putting together a 5.1 mix in the first place, this is roughly how I'd do it:

-Center channel is typically most of your dialogue and on-screen foley, etc.

-Left, Right are used for sounds coming from just off screen (or even towards the edges of screen) plus probably the musical score.

-Left-, Right-surround channels can also pick up the score (if you want to surround your audience with the music) and additional spatial effects (rain, bees, etc.).

-LFE is where you park your 100-Hz-or-so lowpass-filtered explosions, engines revving, heartbeats thumping, etc.

 

When mixing down to 2 channel stereo, most of what to place where becomes fairly straightforward. Just pan and attenuate as desired :)

 

If you let the DVD player make the downmixing decisions for you, you might end up with a mix where the dialogue can get lost in the musical / effects tracks. I notice this quite often when watching DVDs at my parents-in-law's house -- they don't have any sound system hooked up... just the TV speakers. Presumably the elements that are "too loud" were present in more than one of the 6 channels before being remixed by the player.

 

As a side-note, check out Dolby Surround (ProLogic) some time. Here you get to mix 4 channels (L,R,C,S) into 2 stereo channels. The specification is set up in such a way that if it is played back on a stereo-only system, the results are acceptable, but if played through a surround-decoder, you get some decently separated surround channels. VHS, Laserdisc, Beta, etc. have been using this surround system for years, and I bet you didn't complain much when watching movies w/o a surround receiver.

 

 

Anyways.. I'll stop rambling now.. back to storyboarding :)

 

Cheers,

Sean