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Digital to Analog issues

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Justin Ferar
Digital to Analog issues
on Aug 14, 2007 at 9:54:47 pm

I edit video in Final Cut Pro with a Black Magic Intensity Pro Video card. The card has AES/EBU out which I have connected to a Behringer SRC2495 Ultramatch Pro ADDA converter via RCA coax. The converter locks on to the signal with no problems- levels match Final Cut Pro exactly.

The converter has balanced analog XLR outs which I have connected to my Behringer UB1204 Pro mixer which is then connected to my monitors also via balanced XLR's.

The problem is that the analog signal coming out of the converter is about 10db too hot for the mixer. If I send tone out of Final Cut Pro the mixer clips at -10db (according to the converter's meters and Final Cut Pro's own software meters).

Unfortunately the converter has no way to trim down it's output.

Am I doing something wrong or is it common knowledge that there is a 10db mismatch during a digital to analog conversion?



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Rodney M
Re: Digital to Analog issues
on Aug 15, 2007 at 12:20:30 am

In the simplest of terms, 0dB analog equals -20dB digital (to account for the headroom you normally have in analog). Your -10dB in FCP signal is actually +10dB at the mixer, thus the distortion.



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Ty Ford
Re: Digital to Analog issues
on Aug 15, 2007 at 1:08:47 pm

Maybe you're using the mic inputs instead of the line inputs?

A lot of current gear only uses XLR for mics. Line level uses 1/4" TRS jacks and plugs.

Regards,

Ty Ford

Want better productio audio? Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. More at: http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com


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Rodney M
Re: Digital to Analog issues
on Aug 15, 2007 at 2:51:54 pm

I may have misread your post - let me clarify a few things.

What you want to see is tone reference in FCP at -20dB equal 0dB at the mixer. That's the goal, especially if you transfer to analog decks (a little old school, I know). However, if you are creating mixes for DVD, then you are probably pushing the program peaks to as close to 0dB (in FCP) as possible. At that point you probably will distort analog gear. In my experience, I've not seen any analog gear that can handle constant +20dB of headroom without distortion.

Let me restate:

If you have tone set at -20dB in FCP then trim the inputs on the mixer so that the tone is at 0dB at the mixer. Any mixes you create in FCP that keeps the program average at -20dB will then play fine at the mixer without distortion. If you are creating mixes for DVDs that push that average up to say -10dB so that your peaks are close to 0dB, then you should recalibrate your mixer so that -20dB in FCP equals -10dB at the mixer. This will give you an additional 10 dB of headroom at the mixer and should keep you distortion free for monitoring.

Also, I didn't know that AES/EBU could travel over RCA cables. I've only seen AES/EBU on XLR connectors. S/PDIF uses RCA.



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Justin Ferar
Re: Digital to Analog issues
on Aug 15, 2007 at 4:44:54 pm

Rodney, you are exactly right. I am editing for DVD as I usually mix sound right up to zero which would be pushing my analog mixer way over. The mixer can't trim the input, it only applies gain, which is a bummer.

Anyway, Ty was correct that I have the input coming in on mic inputs so I'm going to go and get some XLR to TRS cables for line level input on the mixer.

Thanks for the reply as it was very helpful!



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Justin Ferar
Re: Digital to Analog issues
on Aug 15, 2007 at 4:38:04 pm

Yes, I am using the XLR mic inputs which I think is a problem. Shoot! I don't have any XLR to TRS cables lying around.

Looks like a lunch trip to the musician's store is in order.

Thanks Ty.



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Ty Ford
Re: Digital to Analog issues
on Aug 15, 2007 at 9:28:00 pm

Aha!

Then my job here is done!

::reaches jauntily for a sasparilla and a smoke::

Regards,

Ty Ford

Want better productio audio? Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. More at: http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com


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Ray Palmer
Re: Digital to Analog issues
on Aug 16, 2007 at 1:50:01 pm

[Ty Ford] "::reaches jauntily for a sasparilla and a smoke::"

"Who was that masked man? He's my hero!"


Just don't go into town, stranger. I hear they are gunning for ya.


Ray Palmer, Engineer
Salt River Project
Phoenix, AZ
602-236-8224 office
There are three types of people in this world, those that can count and those that can't.


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Ty Ford
Re: Digital to Analog issues
on Aug 16, 2007 at 5:45:07 pm

:)

Want better productio audio? Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. More at: http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com


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