Some distortion in my soundfiles

[Arvid Unsgaard]

I have some distortion in my sound. Is there anyway to fix it or make it better?

I use Mac so - what do you think?

[Guy McLoughlin]

Can you post a sample of the distortion?

[Arvid Unsgaard]

Here is two small files

on with vocal and dist

and one speach with dist.

http://homepage.mac.com/arvidunsgaar...Sharing30.html

[Chris Soucy]

Sounds to me like headroom clipping, which, if true, cannot be fully "fixed"

There have been a couple of good semi fixes been posted here, but their authors names escape me - reckon they'll pop up before long, or have a good trawl through this forum, the relevant posts aren't that old.

Another good way to find them is to Google - try "sound clipping" etc as the search criteria.


CS

[Arvid Unsgaard]

Originally Posted by Chris Soucy

Sounds to me like headroom clipping, which, if true, cannot be fully "fixed"

There have been a couple of good semi fixes been posted here, but their authors names escape me - reckon they'll pop up before long, or have a good trawl through this forum, the relevant posts aren't that old.

Another good way to find them is to Google - try "sound clipping" etc as the search criteria.


CS

What does it mean with headroom clipping?

[Arvid Unsgaard]

The strange thing is that it not get clipped in the camera.

[Chris Soucy]

is where the signal level exceeds the ability of a circuit to deal with it and results, literally, in the peaks of the sine waves being "clipped" off. If it happens into an A/D converter the result is pretty nasty.

If, as you say, the signal isn't clipped/ mangled "on camera" I'm a bit mystefied (adding hastily that this is getting way out of my comfort zone and would be better dealt with by one of DVinfo's REAL sound guru's).

Can't shed any light onto the NLE either as I'm a PC bod.


CS

[Steve House]

It may or may not be actual clipping per se but it sounds like the signal is too hot for the input and is overloading on peaks - hard to say just where in the signal chain it's occuring without more information.. Tell us a little bit about how you recorded this and what equipment you used.

[Gerry Gallegos]

Sounds to me like the previous assessment is correct, its mild distortion from an input being overdriven, how do you know its not the camera being over driven? if you are looking at meters on the camera, that may not be an accurate way to show clipping as most meters on devices are what is called an RMS (average) level and not necessary PEAK metering. can you explain your signal chain and what equipment you used? the distortion seems mild and you can probably reduce the effect. but sound is like baking, once the ingredients are in there they are impossible to take out, all you can do is try to hide or de-emphasize.

[Chris Soucy]

Just to expand on my previous explanation of "headroom clipping" if, of course, you're interested.

OK, take a pure sine wave. Put it through an amplifier with an amplification factor of say, 10. At the O/P you get a sine wave 10 times the magnitude of the I/P.

All well and good. However, any amplifier has an O/P "ceiling" beyond which it physically cannot go. Lets say our amplifier has a ceiling of +/ - 10, determined by the voltage rails it's functioning from and other factors.

So, we increase the size of the I/P sine wave till the O/P reaches this ceiling. Then we go beyond it. The O/P cannot go beyond +/- 10 so that portion of the peak that "should" go past it is slammed into the ceiling for the duration of that peak.

We now have a sine wave with a flat top. It is no longer a sine wave but a partial square wave. Continue to increase the I/P, so more and more of the signal is slammed into this ceiling.

Take this to the point where the O/P IS actually a pretty good square wave.

We no longer have an analogue sine wave, but a digital square wave. Analogue circuits really, really, do not like digital signals, and will do everything in their power to take the edge off that square, thus becoming a very effective multi band filter.

Run this square wave through a spectrum analyser. Guess what? Our once pristine single frequency sine wave is now litterly thousands of different sine waves of various harmonics of the original frequency, stretching through the entire spectrum. A square wave is, in fact, nothing more than an infinite number of sine waves added together.

So, the moment you drive an amp past it's ceiling, that horrible raspy sound you hear is harmonics of the original being produced in their thousands, the number directly proportional to the amount of "clipping" going on.

It can be produced by "too hot" a mic into a pre - amp, the wick being turned up too high on that pre amp and driving a subsequent stage into clipping etc etc etc.

Feed a square wave (or part thereof) into an A/D converter (as in camera audio to digital tape "a la" DV or HDV) and they get very huffy indeed.

The reason for the "headroom"? This is the margin you must allow in your overall signal level to allow for transient peaks in excess of the average signal level. The less headroom you allow (which usually gives the best signal to following stages) also leaves you less able to deal with peaks, which will, of course, collide with the ceiling, thus giving you more and more clipping.

Allow no headroom at all, and thus force every single frequency in your I/P signal to clip, you unleash a veritable shit storm of er, mess loose on following stages.


Just thought I'd share.


CS

Ps. Whew, got through that with not one mention of "Slew Rate". Must be getting better.

[Arvid Unsgaard]

I use a Sennheiser MKH 50 into a Shure FP 24 and out to a PD170 Dv Camera.

I use the 0db peep to adjust the volume on the camera and then listen all the time on the camera sound.

From the Shure mixer it was line out to the PD170 camera, and line in on the PD170.

So what can I do?

Any plugins or something to get it better.

Thanks for your great help

[Chris Soucy]

If what we are hearing is, actually, clipping, there is not a whole heap to be done.

I am not convinced it could not have happened somewhere in post. The real DV audio guru's can help here, is there any way this is possible?

I never get this sort of problem, so am in total ignorance as to how it could come about, if, as you say, it's clean out of the camera.

If you are 100% certain this is most definately not on the "off camera" sound track, I'm stumped.


CS

[Arvid Unsgaard]

Maybe I couldnt hear it - lucky me I also have a mic on the camera, so maybe I can mix it and use booth.

[Arvid Unsgaard]

Im looking for a clipping restoration tool for osx - someone knowing?

I find some for windows not for osx.

[Arvid Unsgaard]

Originally Posted by Chris Soucy

If what we are hearing is, actually, clipping, there is not a whole heap to be done.
CS

Do you mean its impossible to fix?

Or do it better?