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  #1  
Old 2005-03-30, 05:04 PM
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Clipping in wave files--question

Question for you all. As you may have read I've been doing tape transfers from a tape deck to a standalone. I like to have the recording level as loud as possible without ever hitting the "red" zone.

What is the acceptability in terms of clipping? My standalone has a gauge which lets you know if it's going over 0 dB. At which point, if I see that, I rewind and start the process again at a softer volume. I always test out the volume before recording, but sometimes the volume can fluctuate in a tape, get louder all of a sudden or softer all of a sudden if the taper got knocked around, so it's not always easy to get it right the first time.

So what do you do if there's one or two instances of clipping? Let's say for example the taper hits his microphone really loud which makes the db meter go in the red, but other than that everything's golden and the peak level is under 100%. I take it it's OK to leave the volume where it is and a bump here or there doesn't have to be worried about. But then what if it's 10 seconds of really loud volume? 15 seconds? My concern is that I don't want to transfer at a soft volume for the sake of 15 seconds which happen to be really loud.

What's the consensus on this?
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Old 2005-03-30, 05:14 PM
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Re: Clipping in wave files--question

Several things to keep in mind.

1) You don't want any of the music to go over 0dB. Sounds like you've got that covered.

2) A loud, brief noise like a mic stand ping or bump can be fixed later and I wouldn't let that going into the red have a big effect on the overall gain you use to transfer. You can selectively de-emphasize that noise later so it's not so loud or possible eliminate it entirely depending on some things.

3) The last question is more difficult. Shows can have wide dynamics, from very quiet to very loud. For the purpose of transfer, you don't want to have ANY of the music exceeding 0dB. Otherwise you are introducing artifacts. You can change the dynamics or gain structure later when you edit, if you need to. Gain envelopes in Sony Vegas can be useful for this sometimes, to raise the gain of a particularly quiet track a couple of dB.

Remember, the goal of transfer is just to get the best digital representation of your analog source. You can't always get a "final product" at that stage.
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Old 2005-03-30, 05:22 PM
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Re: Clipping in wave files--question

I appreciate the response

I guess the only thing though is that it sounds better, at least to my ears, when the gain is at the highest level without going over right when you do the transfer, as opposed to raising it later in an editing stage. I also was really referring more to fluctuations in the tape as opposed to fluctuations in the show itself. I would never tamper with soft spots in the show itself. Even if they're pretty soft, if that's how the show was, that's how it will remain. Like I said, if I start to see it go in the red consistently (and not just a bump in the microphone), I pack it up and start again, and I specifically go to the spots that were giving me red and adjust the volume to make sure they don't go in red again. In that instance, I will adjust the volume around those spots, because that's just how the show is.

What I was getting at is adjusting the levels when it's clear that the loudness is a result of a tape problem; i.e. the taper gets knocked around and things go out of whack for 10 or 15 seconds. Has nothing to do with show itself, just has to do with a problem the taper was having.
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Old 2005-03-30, 06:01 PM
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Re: Clipping in wave files--question

I agree, fixing errors that come from the taper's end like bumping of the mic and such is fine, just as fixing a few incidents of clipping is also fine. As for a steady 10-15 seconds of hard clipping, I would think that this would be undesirable under any circumstances. You could either use a hardware limiter set right at the brink of clipping to catch this stuff or a compresser set to a ratio of infinity:1 with the threshold right at -0.2dB or so. This would be inline before the inputs of the standalone. Your other option is to ride the volume fader during the transfer but you have to know the program material very well and need a steady hand to make it sound natural.

It sounds like you're a pretty careful guy, so try it several different ways and listen carefully for what works best. There's no concrete rules in audio engineering, just recommended techniques that usually give the best results.
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