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Mono File Help

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Eric Naylor
Mono File Help
on Jan 11, 2010 at 10:20:56 pm

I posted on these boards earlier looking for help with a mono recording. I recently shot a short film and the long and short of it is that I want to sync the audio with the video and have it ready for playback for film festivals, i.e., on dvd or blu-ray. Here are my concerns/problems:

-will a mono track play out of both speakers during playback?

-the recording seems to be low, registering around -25 dbs to -18 dbs when someone speaks (I'm looking at the levels in adobe soundbooth cs4). I used the match audio feature and I'm able to raise the levels to 0 db on all my audio clips and it sounds alright. Nothing distorted. But I'm just concerned about what it would sound like when being played at higher volume through theater speakers.

-any quick basic steps I could take to make the audio clean and crisp?

Thanks.


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Ty Ford
Re: Mono File Help
on Jan 12, 2010 at 12:53:54 am

Hello Eric and welcome to the Cow Audio Forum.

-will a mono track play out of both speakers during playback?

>> Yes, if you produce the sound properly.

-the recording seems to be low, registering around -25 dbs to -18 dbs when someone speaks (I'm looking at the levels in adobe soundbooth cs4). I used the match audio feature and I'm able to raise the levels to 0 db on all my audio clips and it sounds alright. Nothing distorted. But I'm just concerned about what it would sound like when being played at higher volume through theater speakers.
-any quick basic steps I could take to make the audio clean and crisp?

>> No quick basic steps, but I think you're on the right track. Recorded that low, you might hear some system noise when you bring the level up.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Richard Crowley
Re: Mono File Help
on Jan 12, 2010 at 5:57:46 pm

You can make a mono track play out of either or both speakers depending on how you mix it during production.

The problem when boosting levels that are too low is not distortion. The problem is more likely to be higher noise floor. The noise (both ambient noise and equipment noise) will get boosted when you increase the level of the track.

Having a good monitoring system is critical to creating mixes that will sound good on whatever playback equipment. Playing at higher levels on large speakers will not change how something sounds, but it will make flaws (like increased background noise) more noticeable.

Making "clean and crisp" audio is more a function during production recording than what you do in post-production editing and mixing. Using the proper microphone for the job, and keeping it at the optimal distance and aimed properly are minimum requirements for capturing decent audio.

And setting appropriate levels is also very important. If the levels are too low, your signal-to-noise ratio (SNR) will suffer (too much noise). And at the other end, if your levels are too high, you run the risk of clipping at full scale which is a very severe problem in the digital world.


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Eric Naylor
Re: Mono File Help
on Jan 12, 2010 at 6:22:02 pm

Thank you for the reply. I may have misspoke when I said I recorded at 30-25 dbs. The audio is playing back at that rate, but actually closer to -18dbs when someone speaks. I imported a track from a cd (Bob Dylan's Winterlude if it matters) and that played back at -14 dbs (on average, as it fluctuates). So I think what I'm seeing is just volume level. Do you know what db level it should be at for dialogue?

Also, Adobe Soundbooth lets me save mono files as stereo files and this creates two tracks. Everything appears to be synched.


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Richard Crowley
Re: Mono File Help
on Jan 12, 2010 at 6:45:56 pm

"I may have misspoke when I said I recorded at 30-25 dbs. The audio is playing back at that rate, but actually closer to -18dbs when someone speaks."

Even -18dB seems rather low for speech peaks. I would prefer something more like -12 or -10dB for peaks. Not sure what you mean by "recorded at"?

"I imported a track from a cd ... and that played back at -14 dbs (on average, as it fluctuates)"

That seems rather low for a commercial CD recording. Where (and how) are you seeing "-14 dbs"? Maybe your overall levels (or monitoring levels?) are set too low.

"So I think what I'm seeing is just volume level."

Yes "volume level" is what dB measures. There are not two different things here.

"Do you know what db level it should be at for dialogue?"

I'm not sure what you are asking here? If you mean "what level should I peak speech while recording", then my suggestion would be around -12 to -10dB. If you mean "how loud should I mix the mono speech track in my production mix", then only you can answer that based on artistic decisions. It is not a number that someone can prescribe in an online discussion forum.

"Also, Adobe Soundbooth lets me save mono files as stereo files and this creates two tracks."

So it just "copies" the mono channel into both the left and right stereo channels. If that stereo track is all you need from mixing, then that seems OK. But if this mono track is one of several that you are mixing together for the production, I don't see the point in converting it to "stereo"?

"Everything appears to be synched."

Sync would not be expected to be an issue when simply copying a mono track to left and right stereo tracks. The tracks are identical copies, and redundant.



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Eric Naylor
Re: Mono File Help
on Jan 12, 2010 at 7:09:57 pm

I'm looking at the volume levels in Adobe Soundbooth. It's the long bar at the top of the interface. I simply imported the song and let it play and viewed the levels as it played. It's possible it was closer -12 or -10. I also put something a little heavier on and it reached and went over 0.

You've definately given me enough info to feel alittle more confident playing with the audio. I was having a hard time figuring out what a proper db level should be. Some people were telling me 0 dbs. I appreciate you taking the time to answering and discerning some of my improper audio vernacular (I'm a newbie to this).


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Terry Mikkelsen
Re: Mono File Help
on Jan 12, 2010 at 7:33:26 pm

From the Technical Operating Specifications of PBS:


"3.1.1 The operating level for reference tone and
legacy analog system calibration is -20 dBFS per
SMPTE RP155.

3.1.2 Programs are to have average loudness levels
that fall between -28 dBFS and -20 dBFS during the
majority of a program as measured on a digital meter
calibrated to the RMS/VU ballistic. Average loudness
should not go above -17 dBFS at any point during the
program.

3.1.3 Programs are permitted to have audio levels
that regularly peak near but not above the following
limits using a digital peak meter:
SD: -10 dBFS
HD: -3 dBFS.

3.1.4 Programs must be mixed using dialog level
LAeq metering or subsequent ATSC standard
method. They must have dialog levels with a value of
-24 dBFS ±2 dB. Programs may have peak music or
effects levels up to the level limits specified in 3.1.3
during moments of dramatic impact, as long as dialog
levels are maintained as specified.

3.1.5 Producers must maintain music and effects
levels sufficiently below dialog to insure that a wide
variety of viewers can understand the dialog upon
first viewing, in home conditions with high ambient
noise and moderate program levels."

Tech-T Productions
http://www.technical-t.com

ps-None of my comments are meant to be gospel. Otherwise, I would write a book that provided all the cold, hard, fast answers that everyone assumes are out there. These are the things that I have found to work well with my shooting habits and workflow. Always try things out for yourself and deduce the best workflow for you.


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Richard Crowley
Re: Mono File Help
on Jan 12, 2010 at 8:14:01 pm

Thanks for posting that, Terry. Note that most of those numbers that seem very "low" are based on readings from specialized (read: expen$ive) averaging meters like Dorrough, etc. and not on the kinds of metering most of us have available.

I believe the "bottom line" number in the PBS spec that applies to us who are using ordinary computer-based NLE is...

"3.1.3 Programs are permitted to have audio levels that regularly peak near but not above the following limits using a digital peak meter: SD: -10 dBFS..."

I am a bit surprised at the "-3dB" number quoted for HD. I suspect it means that we can expect the audio levels will be further "adjusted" at one or more places along the transmission path. I'd be happy if they could just keep the audio in sync with the pictures. :-)


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Terry Mikkelsen
Re: Mono File Help
on Jan 12, 2010 at 8:56:39 pm

But still.....-10dBFS is when referencing -20dBFS as 0VU.

Tech-T Productions
http://www.technical-t.com

ps-None of my comments are meant to be gospel. Otherwise, I would write a book that provided all the cold, hard, fast answers that everyone assumes are out there. These are the things that I have found to work well with my shooting habits and workflow. Always try things out for yourself and deduce the best workflow for you.


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Richard Crowley
Re: Mono File Help
on Jan 12, 2010 at 9:16:22 pm

"But still.....-10dBFS is when referencing -20dBFS as 0VU. "

-20dBFS is the pro-standard for tone reference in the digital age. It is equivalent to the "0dB" back in the analog age. It clearly allows for 20dB of headroom above the "reference" level. As you say, it would be the same as PBS specifying back in the analog age that peaks of +10dB were permitted. (And I vaguely recall that WAS something like the PBS spec back in the analog age.)

Note that many users of "prosumer" equipment use -12dBFS as the reference level. This leaves 12dB of headroom, but gets average levels higher above the (somewhat higher) noise floor of prosumer equipment. Some might argue that all of us who record single-system audio to video camcorders are "prosumer" because no video cameras (even high-end "broadcast" models) have really notable audio sections. :-)


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