Subject:Clipped peak restoration possible by hand?

Posted by: pup

Date:5/8/2002 11:04:29 AM

Hello, all. I uploaded a dialogue recording session from DAT into Sound Forge 5.0. Unfortunately, one important spoken word was clipped on the DAT during recording, so there's not much I can do there. Since it's only one word, I thought I could manually fix it in Sound Forge with the pencil tool, rounding off the clipped peaks. Uh...it didn't work well at all. I guess if it was that easy, SF wouldn't have made a Clipped Peak Restoration Plug-In, huh? Needless to say I don't have the plug-in.

Shouldn't rounding-off the clipped peaks have taken care of my problem? Am I missing something? What makes the plug-in so special? Thanks.

- pup

Subject:RE: Clipped peak restoration possible by hand?

Reply by: Rednroll

Date:5/8/2002 1:07:20 PM

The plugin escentially does exactly what you did with the pencil tool. I have used the pencil tool to do this exact same kind of process, sometimes better than the clipped peak restoration plugin. It all depends on how much was clipped off. It's quite possible that there was an error on the Dat tape, which causes a glich (ie lost data), rather than a clipped peak. So rounding off the clipped peaks, doesn't give you back missing data.

Subject:RE: Clipped peak restoration possible by hand?

Reply by: VU-1

Date:5/8/2002 3:52:41 PM

You basically have 3 options:

1) Download the N/R 2.0 demo & try it out on your bad section. Maybe it will work for you.

2) Hunt around in the dialogue to find the same word spoken in the same manner & just cut your bad one out and paste a copy of the good one in. Believe it or not, this really does work sometimes! It may require some fancy crossfading to make it seemless, but I have done it successfully many times.

3) Re-record the bad section of audio.

Jeff Lowes
On-Track Recording

Subject:RE: Clipped peak restoration possible by hand?

Reply by: Chienworks

Date:5/8/2002 4:05:28 PM

Another tactic i've used with some success, weird as it may seem:
- select just that section of the file
- reduce the volume of that section by 6dB or so to give yourself some headroom.
- EQ the heck out of it, boost bass & treble, cut midrange (for example)
- EQ again, using the opposite curve (should restore the original equalization)
- add a tiny touch of short-sustain reverb or a tiny touch of smoothing
- increase volume as necessary to bring it back up to the level of the rest of the file

The idea is that each of these steps recalculates the data and will fill in new details that will cover up the clipped peak. The result may not be very faithful to the original, but it may sound acceptable enough. And besides, no one but you will hear the original to compare it with.

Subject:RE: Clipped peak restoration possible by hand?

Reply by: Rednroll

Date:5/8/2002 9:23:06 PM

Chien, I might have to try this some day just to see how it works. From reading your decription, it doesn't seem very likely this will work. Seems like what you're doing is screwing up the audio so much around the clipped peak that everything becomes a big blur and therefore makes the clipped peak less noticeable. Kind of like having a hole in your roof that's leaking water onto your living room floor. So instead of patching the hole, you rip the entire roof off and turn your living room into a swimming pool. Hey, I like swimming pools more than living rooms anyways.
:-)
red

Subject:RE: Clipped peak restoration possible by hand?

Reply by: Chienworks

Date:5/8/2002 9:44:52 PM

Red, love your preferences ;)

I think the only reason it works is that i confine the affected area as close to the problem peak as possible so that it's duration is almost below the threshold of noticeability. If there's a string of clips that last more than a fraction of a second then my method will be noticeably bad.

The thing that makes the clipped peak sound so bad is the sudden discontinuous change in velocity of the curve. Most anything that makes this change gentler will be an improvement, at least in how the sound is perceived.

Subject:RE: Clipped peak restoration possible by hand?

Reply by: pup

Date:5/9/2002 7:42:22 AM

Thanks, fellers. I initially used an alternate take, but I wanted to save the clipped one in case the client was dead-set on using it. I ended up installing the demo, and sure enough...click...all done. Nifty plug-in. I'm baffled why my pencil trick didn't work, though. Maybe someone could clear that up for me. The restoration plug-in says something about being able to automatically apply peak limiting to the area immediately surrounding the audio clip. Maybe that's what I missed. Also, my clipped peaks were only at the top of the screen - not the bottom. Does that mean anything special in the realm of audio science?

- pup

Subject:RE: Clipped peak restoration possible by hand?

Reply by: Chienworks

Date:5/9/2002 2:56:33 PM

Keep in mind that simply adding a round top to the clipped off wave doesn't change much. The slope may still change sharply at that point. I would think that the clipped peak reduction routine must calculate where the peak would have been based on the slope of the curve, and then redraw that entire wave at a lower amplitude. That would be a tough trick to pull off with the pencil tool.