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Old 06-03-2007, 11:39 PM   #4
Measuring Man
Human being with feelings
 
Join Date: May 2007
Location: Toronto
Posts: 91
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The best method I've found to maximize your converters quality is to determine the relative 0dbv/u of your sound cards converters and use that as a reference point for interfacing with the analog world, both in and out.

For instance, the 002 I use at one studio has a maximum output of +18dbu, easily found on the spec sheet. That means that if I'm referencing any professional gear that uses the standard +4dbu reference, in the computer I use -14 as my reference point, 18-4 = 14db of headroom. So if I'm recording, my analog meters on my pre-amp are reading around 0dbu, and my audio in the computer is averaging -14db. That's average, not peak. In practice, in means my peaks are usually around -6db in the computer, but that can vary depending on what I'm recording. (if you're referencing -10dbV pro-sumer gear ad aprox. 12 to all dbu measurements to get the equivalent -10dbV reference, unless the gear specifies the dbV scale.)

Likewise, if I'm mixing with an average level of -14 in the computer, when I layback to my analog 1/2" 2-track, which coincidentally has about 14db of headroom over +4du, my reference levels will be the same.

In my pro Tools HD rig, the converters are calibrated to be -20db digital to +4dbu analog, that's down 2 db from their stock setting of -18db digital for +4dbu. This is a broadcast standard, -18db digital in Europe. So I have to mix at -20 in the computer and make sure nothing usually goes above -8 (a broadcast maximum reference by the way, found that out the hard way when tapes got sent back) in order to avoid sending analog tape in it's distortion ranges. Other analog gear has much greater headroom, but like your converters it's best not to push it.

I often use tones, just like they used to in the analog days, and still do in post, to check my calibration.

I find if I use the reference levels, my analog outboard gear, and my converters perform at their max. The cheap power supplies in "pro-sumer" gear usually crap out at higher range of their voltages, so the top 3-6db of you converters range can sound strained or otherwise crappier. 6db in digital translates to about 1 bit of resolution loss, but with noise floors, you're only getting 18-20db range to begin with. But 20 good bits is better than 24 crappy ones.

With the advent of peak metering in digital, the art of understanding db's is going the way of the do-do. Which is a shame, 'cause after I finally figured out how db's work, and it took a looooong time, it's really saved my ass from a lot of digital and analog audio problems, distortion being the biggest problem.

I listen back to the ADAT recordings of the 90's where people were told to slam the levels to maximize resolution, and they sound strained and thin. But any tape that properly referenced the ADAt's relative analog point, -15db digital on the original ADAT's is +4dbu on the balanced out and -10dbV on the unbalanced out, sounds amazing, even though it's only 16 bits. Same for many DA-88 tapes I work with.
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