Pyro Industries API-1394PCI Manual de usuario descargar pdf (Pagina 169)

148

CHAPTER 4: THE TIMELINE ■

You can also use Infinite Peak when you do an output of your cut, just in case

you are not monitoring it carefully. (I am not recommending that you not monitor your

outputs! If you don’t, you’re on your own, pal.)

Reset Peaks

Reset Peaks allows you to view new peak holds and ignore the past ones. If we use the

previous example of using Infinite Peak while capturing, you could reset the peaks and

recapture the bad audio after adjusting it.

Set Reference Level

Setting reference and calibration tone levels is a bit tricky. If you refer to the Xpress

Pro manual, you’ll see that the reference level for digital is –14dB. But the reference

levels really depend on what destination deck that you are outputting to.

To confuse things even more, take a look at the Audio tool (refer to Figure 4.17).

There are two scales that vertically measure the audio. The left scale is for digital

audio—note that the maximum level for digital audio is 0dB. Anything beyond that

level is distorted. On the right, analog levels are measured. The levels are measured in

VU (volume units) as indicated on the scale. The maximum level for this is +14.

Here’s what you should do. When outputting to an analog deck (nondigital,

non-FireWire) use the analog scale. The reference level is set to +0 VU, but when set-

ting this level, we use the digital scale. If you look from the analog scale on the right to

the digital scale on the left, you’ll see that +0 VU equals –14 dB in the digital world. So

when setting levels for output to an analog deck such as Betacam, VHS, and any non-

FireWire source, set the level to –14dB.

Are ya with me?

Now let’s look at that scale once again. If we are outputting via FireWire to a

digital deck (DV cam, DV camera, DV deck, etc.), we set our reference on the digital

scale at –20dB.

Now you want to know why on earth you would do this when the manual says

–14dB, don’t you? Well, the original level for digital decks wasn’t set in stone when

Xpress Pro and even Free DV were created. As a matter of fact, it still isn’t today.

What we’re dealing with here is a thing called headroom. Headroom is the amount

of additional volume that the source can go beyond the reference volume without reach-

ing a point of distortion. If you go beyond the headroom, the audio will be distorted.

But when the first digital machines were created, everyone had a different idea

of how much headroom should be allowed. Some said 18 dB, some said 14 dB, and

others said 16 dB. Analog had long been standardized to +14 VU as the highest peak.

But digital levels were not standardized.

As a result, Avid now uses –20 dB as the accepted reference level, with 0dB as

the peak level. This gives us 20dB of headroom, which is a lot, but for quality and

purity of the digital signal, it’s a very good standard.

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Pyro Industries API-1394PCI Manual de usuario Pagina 169