Faking 5.1 surround

[Cracker Funk]

Here's the dilema -

I've got one last festival screening coming up soon. I don't have the money to pay somebody for a professional audio mix, I gotta do this myself. My film currently is mixed to 2.0 stereo. Everywhere it has screened, it has sounded fine.

Mind you, it's never sounded anywhere close to professional, as it was mixed by me, a complete audio newb. But all of the screenings at least sounded like I expected them to sound -- the way I mixed them.

All except one particular screening. 2001 and wheaty were present, to witness the atrocity. The audio would jump back-and-forth, from speaker-to-speaker, right in the middle of dialog. And some of the speakers sounded like they were farting. It was an audio nightmare, and an absolute mystery.

Thanks to this thread, I now finally know what caused it -- my 2.0 stereo mix being played by a 4.1 stereo system. I've communicated with the organizer of the upcoming festival, but he is not entirely sure what type of system they're running. All he knows is that it's a fairly regular theater, with a modern sound system. And I don't want to risk another audio-gate.

Here's an idea that's ran through my head -- trick a 5.1 mix into behaving like 2.0.

You might ask -- why not do a proper 5.1 mix? Because I have neither the hardware, expertise, or time required. My software mixes to 5.1, but I have a 2.0 monitoring system.

Plus, my movie is pretty close to being mono. All of the production audio is stereo, but recorded with a single shotgun mic. The stereo effect is not very dynamic. The most notable dynamic stereo effects come from the music. With that in mind, here's how I think I might easily adapt my 2.0 into behaving, when played on a 5.1 system.

Front-center speaker: Original 2.0 stereo mixed-down to mono
Front-right, front-left, rear-right, rear-left: Original 2.0 stereo split into two separate tracks, left and right, and panned accordingly. I kinda think that is so simple that it should work.

But here's the confusing part for me -- frequencies. In the above breakdown, I only listed the first five speakers. What about the bass? At what frequency should I split bass speaker away from the rest? I don't want any of my surround speakers farting!

Also -- which frequency-range is most associated with dialog? Cuz I thought I might do a ghetto-style Joseph Pro Logic. If I raise the mids and drop the highs and lows for the center speaker, then that should accentuate the dialog, no? And conversely, I lower the mids for the left and right speakers.

Haha! I know this is ghetto as shit, but it can't hurt to try, no? At least, I think I can improve on the current 2.0 mix. Any suggestions?

 

[MetalRenard]

I don't know about the rest but I don't advise you mix your stereo down to mono in the front speaker because you risk creating all kinds of problems.
For starters it will be a phase nightmare and all kinds of volume issues will come up.

 

[Cracker Funk]

Cool, thanks man.

Also, I found the answers to the other questions I asked (regarding frequencies). The search-terms I used to google last night didn't lead me where I wanted, but tried a new search today and found it.

 

[Alcove Audio]

I know that A.P.E. will go ape sh1t (please excuse me ) since audio post is his specialty, but here goes anyway...

The issue is one of balance. You will have absolutely zero idea of how your "fake" 5.1 mix is going to translate into a real world situation. You do have an option open to you, not at all optimal.

I'm 96% sure that your mix is stereo interleaved. Mix it again to Lt/Rt. You can now put those two channels into Front Left and Front Right of the 5.1. Burn a DVD copy, play it on your home system and see how it sounds.

I would strongly urge you NOT to try to play with the rest of the surround speakers. You have zero point of true reference.

 

[Cracker Funk]

Thanks, Alcove! I really appreciate the advice.

And, if A.P.E. (or anyone else) is getting annoyed reading this, I hope they'll understand that this movie was always intended as a showcase of what just me and a few actors could do, on our own. I never had any illusion that we'd achieve production values of much worth. And, it's also true that there's no way I ever do this again -- I'm only going to make another feature if I can afford to hire pros for jobs like this.

 

[Mannie Bothans]

And some of the speakers sounded like they were farting. It was an audio nightmare, and an absolute mystery.

Sometimes, some quotes on this forum just scream, "Add me to your signature file."

 

[Modern Day Myth Prod. LLC]

Seriously look to acquire Sony Vegas Pro for the future. Creating a Surround 5.1 Mix is as easy as selecting NEW and PROPERTIES audio output as Dolby Surround 5.1 and all the audio tracks appear on your time line for the audio. In the watered down version of Vegas Movie Studio for around $100, the tracks are even labeled Center, Left, Right, Base, Left Center, and Right Center and you can drop your audio accordingly onto the audio tracks.

And, you can add additional tracks onto the time line.

I will be experimenting with it more in the future.

 

[AudioPostExpert]

1. Front-center speaker: Original 2.0 stereo mixed-down to mono
Front-right, front-left, rear-right, rear-left: Original 2.0 stereo split into two separate tracks, left and right, and panned accordingly. I kinda think that is so simple that it should work.

2. But here's the confusing part for me -- frequencies. In the above breakdown, I only listed the first five speakers. What about the bass? At what frequency should I split bass speaker away from the rest? I don't want any of my surround speakers farting!

3. Also -- which frequency-range is most associated with dialog?

1. Not only won't you have any idea of the balance of the centre channel or surrounds (as Alcove mentioned) but you're going to have all kinds of interesting phase effects between all 5 of the main speakers. To be honest I'd love to hear what it sounds like, it should sound pretty wacky and you would get different wacky effects depending on where you sit in the cinema.

2. The bass is not "split" in cinema sound systems, only on home cinema bass managed systems. In cinema 5.1 systems the LFE channel is completely discrete. The range of the LFE channel is usually 20Hz to 120Hz but can be lower and the range of the 5 main channels is around 20Hz to 18kHz. You should avoid using the LFE channel unless you know what you are doing, have the right equipment and a properly calibrated room. I'm not saying this to appear big or clever, ignore this warning at your peril!!

3. Dialogue usually occupies the range from around 80Hz to about 12kHz, removing frequencies within this frequency band will have a damaging effect on the dialogue depending on how much you remove and the frequency content of each individual actor's voice.

I'm 96% sure that your mix is stereo interleaved. Mix it again to Lt/Rt. You can now put those two channels into Front Left and Front Right of the 5.1. Burn a DVD copy, play it on your home system and see how it sounds.

This won't work I'm afraid. LtRt is at least a 4 channel audio format, so you need to know what is happening in those 4 channels.

Creating a Surround 5.1 Mix is as easy as selecting NEW and PROPERTIES audio output as Dolby Surround 5.1 and all the audio tracks appear on your time line for the audio. In the watered down version of Vegas Movie Studio for around $100, the tracks are even labeled Center, Left, Right, Base, Left Center, and Right Center and you can drop your audio accordingly onto the audio tracks.

Your suggestion will not give a 5.1 mix, it will give 6 channels of unmixed audio. To mix the channels, you first have to be able to hear them and then you have to be able to balance (mix) them. You can only do this accurately with a full sized cinema sound system.

CF: Your two lowest cost options are: 1. Buy another speaker and create at least a 3.0 mix (Front Left, Centre, Front right) or 2. Encode your stereo (2.0) mix into Dolby Digital.

Option 1 is far and away the better solution. Option 2 should avoid the channels jumping around, as in theory it should bypass the LtRt decoding processor but you will still have the usual stereo (2.0) problems depending on where you sit in the cinema (as explained in the thread you linked to). But, there is no way of knowing for sure how the festival will rig the sound, so your 2.0 Dolby Digital mix might still end up being routed through the LtRt processor and then you'll be back where you started!

G

 

[Cracker Funk]

Thanks, Post! I really appreciate the help.

I am sufficiently convinced that my original idea won't work. And whatever I do has to be done tomorrow (festival is next week).

How about this option? I split my current 2.0 mix into hard right and hard left. I make those my front-R and front-L, in a 5.1 mix. And then I just leave all other channels silent. (Is that what I'd be doing if I encoded to Dolby Digital?)

I re-read the original thread, in which you warned of these very types of issues, and I noticed that you pointed out that 4.0 Dolby was common from the 70s to 90s. The theater I'll be screening in was definitely built in this century, and it is a multi-purpose theater on a school campus. I'm thinking that makes it pretty likely that their screening system will work just fine with my 2.0 mix. It's a gamble to leave things as they are, but I'm beginning to think the odds are in my favor.

 

[AudioPostExpert]

How about this option? I split my current 2.0 mix into hard right and hard left. I make those my front-R and front-L, in a 5.1 mix. And then I just leave all other channels silent. (Is that what I'd be doing if I encoded to Dolby Digital?)

I re-read the original thread, in which you warned of these very types of issues, and I noticed that you pointed out that 4.0 Dolby was common from the 70s to 90s. The theater I'll be screening in was definitely built in this century, and it is a multi-purpose theater on a school campus. I'm thinking that makes it pretty likely that their screening system will work just fine with my 2.0 mix. It's a gamble to leave things as they are, but I'm beginning to think the odds are in my favor.

Yes to the first paragraph, that is option #2 I suggested in my previous post.

In the '70s to '90's Dolby Stereo, LtRt (LCRS) was the most common primary playback format. It is still extremely common today but not as the primary playback format. The most common formats today is 5.1 Dolby Digital (DD) or straight wav files for DCP (min 3.0). However, a LtRt mix is still included on all 35mm Film projection copies as a standard requirement of the print-mastering process. Cinema playback systems are designed to ignore this LtRt mix unless a fault occurs with the DD stream, at which point playback will automatically switch to the LtRt mix. If you only supply a 2.0 (LoRo) mix, many/most cinema systems will interpret this scenario as a failure of the 5.1 mix and switch to decoding the LoRo mix as a LtRt mix and this is what can cause parts of your LoRo mix to start jumping around to/from different speakers. You have to realise that LoRo stereo has never been a supported audio format for cinemas because of the lack of a centre channel and the failure of the phantom centre positioning which that causes. So cinema systems never expect to encounter stereo audio, unless it's an LtRt mix and even then only as a backup. Encoding your LoRo mix as a 2.0 DD mix should fool the processor into playing your mix back as a 5.1 mix but obviously with nothing on the centre, surround or LFE channels. I said "should fool" because it depends on which media type you are supplying your film and how that media playback device is connected to the system. For example, if you are supplying a DVD and the audio output from the DVD player is connected to the cinema system, the cinema processor may still interpret this audio as a LtRt mix (depending on the exact routing and the settings of the processor). If on the other hand the digital outputs are connected from the DVD player outputting a DD datastream to the cinema processor, the processor would probably decode and play it as a DD mix (depending on the processor's settings), even though it only contains an LoRo mix. As you can see from this, how the DVD, BluRay or HDCAM playback machines are routed to the system and the settings of the system is critical but most cinema operators/managers have little/no idea what they are doing when it comes to the often complex sound system routing/equipment/settings, which is a serious problem when it comes to festivals and playing back films from different media types. Of course in normal usage the cinema operator doesn't have to think about any of this because the cinema is already setup for playback of a specific media format (either 35mm film or DCP). To avoid all these issues is why Dolby support most of the major international film festivals by supplying at least one of their own technicians (plus usually additional playback equipment) for the duration of the festival.

One last point, as we have discussed in the previous thread, 2.0 stereo never works well in a cinema. How badly it works depends on the cinema. The wider the cinema (and the cinema's screen) the worse a LoRo mix will sound to more of the audience. Looking at the photo of your specific cinema, it does not appear to conform to Dolby specifications because the proportions are incorrect. It's is too long and narrow and the ceiling is too low. As this is not a Dolby approved cinema they don't need Dolby approved sound equipment, so who knows what playback equipment they have installed, it may only be a LoRo stereo system anyway! Also, because it looks too narrow for it's length and height, the sound probably won't be particularly good to start with, so the usual problems with a LoRo mix in a cinema may not be so obvious in this specific instance (except for those audience members sitting off-centre, near the front).

G

 

[Cracker Funk]

That's very helpful, thank you so much! I'm going to encode to DD. And I think you're probably right about this theater -- I can't imagine many college halls have anything more sophisticated than 2.0.

 

[AudioPostExpert]

You said in your OP that the theatre manager said they have a modern system, like a regular theatre. Well, all regular theatres have a 5.1 system, if they only have a 2.0 system then they probably don't have a Dolby cinema processor, just a DVD or BluRay player hooked straight up to the amps in thier sound system. If this is the case, then you're not going to have a problem with sound coming out of the wrong speakers and you don't need to encode your LoRo mix into Dolby Digital (DD).

BTW, the normal setting for creating a DD master for theatrical playback would be a DialNorm setting of -31, the most common setting for commercial DVDs is -27 and a -24 setting is used for digital TV broadcast. As you don't have a calibrated mix room and as there is a fairly high probability that the cinema itself is not calibrated either, I would probably recommend a Dialnorm setting of -27.

Good luck and let me know how it goes.

G

 

[Cracker Funk]

I took your guys' advice, and everything went swimmingly! Thanks again!