Reference Level for Broadcast Audio
 

I apologize if I get any of the terminology wrong; I am not really an audio guy.

I work for a small production agency. When we output to a Beta Deck we use a -12 db reference tone to set the level on our mixer and then on the the Beta Deck. We make sure the reference is set to 0 db on the mixer and Beta Deck though. I never really thought about it until recently but should the mixer and beta deck levels be at -12 db as well when the tone is playing?

SMPTE specs call for 0VU tone to be set to -20dBFS, peaks not to exceed about -10 dBFS

OK, please correct me if I am wrong because I am a duffer when it comes to audio.

When I run a 1khz tone at the beginning of the tape, Final Cut Pro's audio meter should be at -20dBFS and the VU meter on the beta deck should be at 0 and nothing should register higher than -10dBFS on FCP's audio meters.

That's the gist of it. This evening I'll look up that exact numbers for you.

Thanks a lot for your help, Steve. I am trying to get a little better at the audio production side of things.

One of the problems in translation is the FCP meters are digital peak reading while the Beta deck (I'm assuming Beta and not DigiBeta) meters are analog averaging VU meters. They're really apples and oranges.

if you do that, you clipped the beta deck out. the problem is its all relative. what you do in your NLE and what you put to analog tape are TWO different things. In digital land, the spec is -18, not -20, with peaks hitting -12. thems the specs I've been handed from numerous TV stations. thats digital.

in ANALOG its all relative. this means what ever you set as your digital level = 0 analog, you don't want peaks going more than 3db above. techincally, betaSP will take +6 over zero, but since so many folks are using UVW series machines that indicate clip on the meters at +4, don't do that ! instead keep you peaks to not exceed 3db of your reference level. I preffer to mix at -12 = 0 to maximize S/N ratio and other stuff within the digital environment when stuck with 16 bit audio. therefore if I set -12 digital = 0 analog and don't let peaks past -9 digital, all is good. same as mixing to -18 digital with peaks not going past - 15. of course if you want to save a lot of time, get a real analog compressor and set it as a peak limiter. this is what I do to catch and fix the occasional peak when going out to analog so save a lot of time. sure some folks may say use a compressor in the NLE, but it just doesn't work the same unless your NLE ( like Prem Pro ) can apply the compressor to the final output channels rather then each clip or track. big difference between the two.

The specs I have been given by national broadcast networks differ from what you suggest. And are exactly what Steve House has posted.

Digital for 0VU tone to be set to -20dBFS

I might add, conventional analog broadcast and VHS tape has about 8db headroom. So setting peak limiting to -12 dBFS in your NLE might be a bit safer than the -10 dBFS I originally suggested. Also adding, "-20dBFS" holds true when reference level 0VU corresponds to an actual signal level of +4dBu.

well the problem is there is no real standard in digital audio. I once went thru 4 sets of specs before finally having a conferance call with a head engineer and two other guys before getting the real specs because none of them new. national network BTW. conversation was over in 2 minutes, but before I got to there everytime I requested specs, I got analog ones. the best one I got was for 1" and reference to how the SC wasn't allowed to vary by more then such and such. Another they replaced BetaSP with HDcam which was just as funny, I think ;\

There is so much irrelevant discussion of digital signal levels in this thread - Beta and BetaSP are analog. If you end up with meaningful program material below -20db you're going to have one noisy tape, the noise floor aka. tape hiss *will* be audible when the tv engineer (cursing) turns up the deck outputs.

Fuggetabout what the equivalences are in the digital world - doesn't matter. What matters is that tone goes on the tape at 0VU, and that program peaks hit at least 0VU. Some stations say peak to 0, some say peak at least to 0.

What Steve Oakley said!!!

The VU meter on the record deck is the *only* meaningful reference. What the customer/tv station wants is the only meaningful standard. Use any digital workflow you want to get there, but watch that VU meter!

and the peak meter.

Regards,

Ty Ford

To add insult to injury, what TV wants and what film wants, are two different things. But then, the title of this thread is "....Broadcast Audio"

You're right in that what gets to the tape is what counts. That's why I added the bit in my last post, that according to SMPTE, reference tone at -20dBFS digital should produce an output level of +4dBu which in turn should result in a reading of 0VU on the analog recorder's meters. If things aren't calibrated throughout the entire chain, all bets are off. And just to make it interesting, the EBU uses a 0dBu reference tone set to -18dBFS digital.

One problem is the VU meter is not a peak reading meter so peaks can go too hot while the VU meter sits there well behaved and apparently within limits.

'The Truth' is visually right here.