Fix Clipping on Multiple Files

Hi, and sorry if this question is basic. I’m fairly new to Audacity and am no audio editing expert.

I have a large collection (a few thousand files) of music, some downloaded and some ripped from CDs. All are presently in flac format. Now, quite a few, but by no means all, of them have clipping (red lines on the waveform). I suspect that a lot of this clipping is in the original recording, but a lot has been created at the very start (first 400th of a second or so) of files that I’ve ripped over several years using K3b.

I want to fix this clipping in my entire collection, without redownloading files or re-ripping all of my CDs. There are far too many for me to manually fix every file, or even to load every file in Audacity to find which particular files have the problem.

I’ve tried creating a macro to normalise the peak amplitude to minus half a decibel, plus deleting the first 400th of a second of each file, and applied it to lots of files at once. This successfully removes the clipping in any files that has any, but it applies the effect to all the files, and the result is that a lot of music that is originally very (relatively) quiet is made louder that I want it to be.

I know that there is a plugin called “clip fix”, but it doesn’t seem to work in the same way, and I don’t seem to be able to successfully remove the clipping in the offending files as easily as simply applying a normalise batch macro to the whole collection. Can anyone point me in the right direction, bearing in mind that I’m a bit of a newbie and may need detailed instructions?

If you normalize to -0dB or have a limiter at -0dB, there may be samples which are exactly at peak. Audacity can’t know whether that’s what’s going on or whether there is actual clipping happening, so it shows you the red lines.

Granted, normalizing to 0dB is generally discouraged because of this and you technically can end up clipping anyway during playback as the inter-sample interpolation may exceed 0dB now, but unless you can actually hear any distortion, it’s probably easiest and safest to simply leave the files be.

Is that a defect in K3b?

If you ripped them to FLAC and you didn’t do any editing/processing to cause the clipping, then re-ripping should fix the glitch at the beginning but the clipping will have come from the original CD so re-ripping won’t help with that.

Some Loudness War CDs & MP3s are intentionally clipped to get “extra” loudness. They can keep pushing-up the average level and the loudness even though peaks can’t go any higher… The distortion also adds to the perception of loudness.

Expanding on what LWindterberg said,… Normalizing or otherwise changing the volume won’t fix clipping. You still have the same wave shape… Lowering the volume simply “hides” it from Audacity.

Audacity is just checking levels and showing potential clipping. You can get false positives or false negatives.

Yeah, that could be a problem. Most “quiet music” is normalized (or nearly normalized) and it just has a lower average level. But you can’t count on that.

The Clip Fix effect tries to restore the waveform but it’s impossible to know the actual original height & shape. When I tried it a couple of times, it made the waveform look better but it didn’t fix the sound. In my case it was a “loudness war” CDs that probably had lots of other “damage”. Clip Fix probably works better if you have “pure clipping”.

And you wouldn’t want to run Clip-Fix on any good files.

Somewhat related - MP3 changes the wave shape. Some peaks get higher and some lower. MP3 can actually go over 0dB without clipping and Audacity can “show clipping” even if it’s not really clipped (false positive). But your DAC can’t go over 0dB so you can clip your DAC if you play it “full digital volume”. As far as I know, this slight clipping isn’t audible, and we already know that MP3 is lossy so it’s not something I worry about. But some people do lower the volume (or normalize to -1dB, etc.) before making an MP3.

It could be. I’m not sure, and haven’t tried chasing it up. It seems to occur when I rip from CDs into one file per track. The effect is only very short, but is picked up as a loud click on playback. I haven’t ripped any CDs lately, but perhaps next time I’ll try a different tool to do it with.

As far as the Loudness War issue, if I’ve understood the meaning, I doubt that’s the cause of the clipping mid-track on the music in my collection, as its mostly classical music, which probably (hopefully anyway) wouldn’t be the type of music where people boost volume at all on recordings. Maybe I’m wrong…

I take your advice on not using Clip Fix, and thanks for your other thoughts.

Thanks for your suggestion. Maybe I’m just being fussy over nothing. After all, it’s not as if I have the skills to actually improve the sound. I think I’ll probably just selectively go over what I’ve collected, and check any files that sound relatively loud - particularly youtube downloads, which seem to be the worst offenders on occasions. If I open any using Audacity and they’re full of red lines I might try fixing them, or I might just dump them and look for a better recording.

As for the clicks at the start of K3b-ripped files, I think it’s time I looked for a different ripping tool. K3b is easy to use, and does a lot, but I only ever use it for ripping CDs.

I agree. Classical music shouldn’t be clipped and it should have little or no dynamic compression. A few occasional red lines may just mean that it was 0dB normalized and it’s just the peaks hitting 0dB.

YouTube uses loudness normalization which tends to bring down the volume of most popular music so that’s going the “hide” the clipping from Audacity. But it’s likely boosting classical. They shouldn’t be boosting into clipping, but YouTube uses lossy compression and that might boost some peaks. If somebody uploads an MP3 to YouTube, they re-compress it to whatever format they use. Then depending on how you “download”, it may be compressed for a 3rd time!

If you re-rip, try to find a ripping application that supports AccurateRip. It checks for errors by comparing to an online database. (On Windows I use EAC or CueRipper.)

That could be what’s happening with the files I’ve downloaded from youtube, but I do find that every fifth or sixth download has some clipping in. Every so often it’s widespread throughout, and spoils the sound quite a bit. For instance, one I recently downloaded, but which is certainly not the worst (I tend to just delete those), is Rachmaninov Symphony No.2 - YouTube .

Anyway, thanks again for your advice about using AccurateRip.

Thanks again. I use Debian, so I’m giving Freac a try. It looks good, and upon first use it’s fairly simple, and works without issue.

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