Correct Audio Levels

rdobbs wrote on 8/16/2008, 7:07 AM

All of the Sony documentation instructs you to run audio levels as high as possible with out clipping (just below 0 db on a digital meter). My professional training tells me that the correct conversion from an analog VU meter is that 0 db in analog equals -20 db on a digital meter. So to insure that my levels match what other professionals are producing, should I use (as loud as I can get it without clipping) or -20 db (digital) as my guide?

Comments

musicvid10 wrote on 8/16/2008, 8:19 AM

There were so many weighting factors devised for analog VU scales that you will drive yourself crazy trying to figure the relationships to dBFS. Often, VU measurements were a function of power, which is a nonfactor in the digital world.

Best real-world advice on dBFS meters like Vegas and Sound Forge is that loudest peaks should be somewhere in the -2.0 to -0.1 range, with program material somewhere in the -6dB to -24dB average (RMS) range. Personally, I opt for the lower (-16dB to -18dB RMS) end in most of my live recording, trying not to let any peaks clip, and then normalize with a little upper range compression if necessary. There is always a tradeoff, and if your noise floor is high, you may want to record a little hotter and let a "few" inconsequential peaks clip, if you're willing to find them and smooth them or use a little "restoration" in post.

Those that follow the old analog tape convention without understanding the differences, i.e., recording hot and allowing +3dB to +6dB peaks, are asking for bad results, especially when there are extreme dynamic differences, such as when recording drums. Digital recording has a hard ceiling, where analog tape had a high floor. You can almost always save a digital recording that was made too low, but one that is too hot is only good for torture. I try not to hit my head and not get my feet dirty at the same time.

rdobbs wrote on 8/16/2008, 8:34 AM

Thanks, good stuff....that info should be in the program documentation.

LarryP wrote on 8/16/2008, 2:20 PM

A nice VST "analog" simulation is available for free from:
PSP Vintage Meter

SF has better metering but from within Vegas I've found this little plug quite helpful.

Larry

musicvid10 wrote on 8/17/2008, 8:24 AM

There is also a nice assortment of free PPM meters from Paul Marshall.
There is even an audible one for the visually impaired, as well as several led and analog styles.
http://www.darkwood.demon.co.uk/PC/meter.html

These work the old way, off the "Record" device in Windows sound properties, not as a plugin, so they are probably a little harder to use, but have really nice, very accurate displays.

ALSO: Here is an informative set of resources on PPM from the BBC. You can even download their 900MHz -18dBFS reference tone.
http://www.bbcradioresources.com/programme/glossary.html

jbolley wrote on 8/18/2008, 8:21 AM

Rdobbs,
The reference level (such as -12dBfs = 0 dBVU) is a function of your analog to digital (and back) converters. If you're looking for such info it won't be in vegas, it will be in your hardware documentation. As said in earlier posts it almost doesn't matter in vegas as long as you're not clipping but it is crucial to understand in the analog world.
Jesse

newhope wrote on 8/29/2008, 6:31 AM

It all depends on the end use of the audio you are creating in Vegas. Internationally there are many standards. Typically the -20DBFS = 0V.U. is a broadcast standard used in the US and countries like Australia for broadcast systems. Other countries and regions use differing standards such as -18DBFS = 0V.U

The analogue/digital relationship is the historical background to these standards but they exist to allow correct levels to be maintained in broadcast chains.

Conversley in music and CD production maximising signal is the norm hence making sure the signal reaches close to 0DBFS at its maximum is normal. Similarly in Dolby Digital mixing the signal can reach up to 0DBFS.

So if the product you are making is destined for CD, DVD and general domestic use then maximising the signal to just below 0DBFS is your best choice.

If your product is destined for broadcast then sticking to the broadcast standards for your region is the best course of action.

New Hope Media

rraud wrote on 8/29/2008, 10:44 AM

In addendum to New Hope Media's "broadcast level". To clarify for uninformed camera ops' and picture editors, the -20dBFS is the REFERENCE level, Most networks (at least here in NYC) specify this in their submission guidelines.... further stating; PROGRAM audio peaks must not exceed -10dBFS.

This digital '0' was confusing to many way back when the R-DAT format first made it's appearence. (or as some say, "reared it's ugly head") (-18dBFS =0VU) I still find this true all the time, where a camera op will tell me the audio is "too hot", because it has exceeded the -12 (or -20) tic on the camera's meter.... or worse yet, change the levels without asking me, which I had so painskakinley calibrated (and taped down)
Adding to the confusion, some of the Panasonics' meter markings are colored red from -12 to 0, not to mention some NLE's meters are nothing short of bizarre. So to conclude my rant, Reference level and peak program level should not be confused.

newhope wrote on 8/29/2008, 9:17 PM

Reference levels do vary and the levels I referred to in my previous post I should have stated relate only to a steady state signal, in this instance I was referring to line up tone.

Hence if you play a 1KHz line up tone on a system set up for -20DBFS = 0VU then on a 'true peak meter' the tone should display at -20DBFS on a VU meter it should display at 0 VU.

However program signal isn't steady state and it will show quite different levels.
As rraud has indicated most broadcasters adherring to the -20DBFS=0VU standard set the maximum permissable audio program signal to -10DBFS.

If you have program signal that is peaking to -10DBFS it will also peak close to 0VU on a correctly aligned VU meter, subject of course to frequency content and the application of any compression and limiting devices if used. This shows the difference in the way each of these types of meters show tone as opposed to program. The less used PPM meters would display tone typically at -9dB and peak program to 0dB in a system lined up for -20DBFS=0VU.

The actual real peak should be -8DBFS but as most meters don't accurately display that then the lower compromise of -10DBFS was chosen. BBC typically require a -12DBFS signal peak as the maximum permissible.

In the end though it is the final use of your product that will predicate what levels you should choose to use. Broadcast reference levels are really only necessary if the end product is destined for the broadcast medium.

Though they have the benefit of allowing some headroom during recording as well. We have all been in situations where the unexpected peak goes way through the maximum we were expecting during recording. If you have 10db of headroom afforded by setting up for a maximum peak of -10DBFS at least you are less likely to hit that magic 0DBFS and run into digital distortion. Levels can then be adjusted back to correct limits during post production/editing for the odd peak over the set limits.

That said if you are producing for DVD , Dolby Digital (AC3) or CD then you can choose to peak your signal to just short of 0DBFS.

New Hope Media