Clipping after normalize and Eq

farss wrote on 1/28/2004, 5:09 AM
Something I don't understand is going on.
I have a track that's down in level so I turn on Normalize and then apply Eq, just low and high shelf, 12 dB rolloff to -infinity, no gain anywhere. But I then find I've gone gone 1 dB over at one point. Fortunately CDA picked this up before I burnt to CD.
Could anyone explain to me how this can happen?

Comments

marcarotsky wrote on 1/29/2004, 11:14 AM
sometimes the inherent nature of EQ'ing works in funny ways. i noticed the same problem in sound forge. even though you didnt add any "gain" in frequency ranges, you just added "rollofs", it tends to brighten the rest of the spectrum. when you drop off bands, it brings or brightens the other frequency ranges a little bit. if you are almost at 0 db as it is, when you run an eq rolloff you may tend to bring the rest of the spectrum out a little bit and cause it to clip. it works a little like compression. with compression, even though your intention is to smooth out frequencies, or add more thump to your kick, it tends to brighten the rest of the frequency range. even though you are not adding any gain to any specific frequency. hope i am explaining this well. 2 suggestions...1. try to mix down to around -.5 or -1 db. (this way it gives you plenty of room for mastering) 2. use a good plug-in like sound forges noise reduction (clipped peak restoration) if you are clipping, (in a minor way) this restores it to "0" db and works great. it will not make magic, meaning if you are clipping at +5db, dont expect anything to help you out, its back to editing!!!!
HTH
--marc
farss wrote on 1/31/2004, 4:56 AM
Well what I ended up doing was measuring my max sample level in SF, taking a couple of dB off that and setting that as master gain in Vegas with Eq on the track and all is well. I was only clipping by 1dB for about 10 samples in 45 minutes so I doubt anyone was ever going to notice but I'e redone about 3 hours of material just to be on the safe side.

You explaination is sort of what I'd figured as well, it makes sense in one respect but I still don't see how the maths work but I really don't have a better explanaition myself.
Ah,
I remember now, long ago when I learnt electronics and 1st, 2nd and 3rd order filters and all that stuff. They have a slight bump at the corner frequency and the higher the filter order the bigger the 'bump'. Now the offending section had a lot of energy right at the corner frequency of the low shelf!
I'll sleep better tonight.
bgc wrote on 1/31/2004, 11:21 AM
why not flip the chain around? (eq then normalize)?
Rednroll wrote on 1/31/2004, 11:33 AM
Farss,
I tried to post quite a long response back to you a couple days back, and when I went to hit post, the Sony severes wouldn't except it, and away went my big long lengthy explaination. In summary you are absolutely correct. I gave an explanation of a butterworth EQ. If the digital eq is modeling an analog EQ like a butterworth highpass filter, then it will have the increased frequencies at the bump like you mentioned, and the sharper the Q of the filter, the higher the bump.

:-) I also went onto byotch slap you for doing the normalize, then EQ. Normalization should always be the last process you do. It's called "headroom". Use it!!! Audio engineers have been using it for years, obviously there's a reason for that as you found. If you dance around on the edge, eventually you're going to occassionally fall off the cliff a few times.
farss wrote on 1/31/2004, 9:03 PM
Red,
you're right, I deserved a kick in the head for not thinking through what I was doing. Problem solved and hey I LEARNED something. In my life I've learned that if you figure it out yourself or maybe take someone else's advice but so long as you understand the why then you're miles ahead.

Funny thing about headroom. Right now I'm capturing a few hours of video off SP tapes, dual mono stuff, one track voice over, other M&E.
Anyway I'm wondering why some of the VO has horrid plops in it. So I look down at the meters on the playback deck and guess what, hard against the stops!

Now these tapes are from a business that has a shingle out the front and charges serious money, I've got only a years experience in the video game and I'd know better than to let that happen.

What's worse it sounds like each bit of VO was recorded with different mics and different gear, even on my cheap monitoring gear it sounds very distracting. I think when I've got the money I'm going to to get a small kit of good audio gear. I'll never make any money out of it but it'd be nice to do a job for a change that wasn't cleaning up some else's mess.