Red Lines In The Audio Graph


It’s probably nothing, but I have noticed this a couple of times and was curious if it is important or not.

I have noticed recently these red lines appearing in the audio graph as attached. It has only appeared in pre-recorded files that I have brought into Audacity for editing. I have never seen them in anything that I have recorded directly through Audacity.

Screenshot (47).png

It’s probably nothing

It’s something.

That’s where Audacity’s monitors have detected a point of audio that got too big. There are a number of different ways to measure overload, but the way Audacity does it, it thinks those red bar points are distorted. At the very least, they are points where sound damage is very likely and you should pay attention.

One way to get damage like that is to do your production in a nice, stable, perfect quality WAV format, make it as loud as you can without causing distortion and then burn an MP3.

The act of creating MP3 format can change the volume slightly. Nobody will notice it by listening, but there could be little points of distortion here and there that were not present in the WAV.

That’s why the audiobook mastering suite leaves a half-dB of slop room so that doesn’t happen.


[u]Show Clipping[/u]. In reality, it’s showing potential clipping.

This can get kind of confusing…

Clipping is distorted flat-topped (and flat-bottomed) waves.

0dB is the “digital maximum” (1.0 or 100%). Your analog-to-digital converter (ADC) and digital-to-analog converter (DAC) are hard-limited to 0dB. If you try to go over you’ll get clipping. For example, if you “see red” immediately after recording you probably clipped your ADC because it’s very unlikely that you hit exactly 0dB without “trying” to go over. “Regular” (integer) WAV files and CDs are hard-limited to 0dB.

In the analog domain you can clip a 100W amplifier by cranking-up the volume and trying to get 110W out of it.

Audacity itself uses floating point so there is virtually no upper (or lower) limit and Audacity itself won’t clip. For example, you can boost the volume or boost the bass in Audacity the peaks might go over 0dB and show red (potential clipping) although the waveform isn’t actually clipped. If you play it at full volume you’ll clip your DAC, but if you play it at lower volume you might not get clipping. If you export to WAV or make a CD, it will be clipped. But the data isn’t actually clipped (yet) so you could use Amplify to reduce the volume before exporting and you’d be OK.

MP3 can also go over 0dB without clipping, and like Koz says MP3 encoding can boost some peaks. So, many commercial MP3s or MP3s you rip from CD yourself will “show red” because the peaks are going over 0dB even if there is no real clipping. But, if you play those MP3s at full-digital volume you will clip your DAC. Or, if you make an audio CD from that MP3 it will be clipped. I’ve never heard of a case where that slight clipping was audible but some people like to reduce the volume before encoding to MP3.

Some commercial “[u]Loudness War[/u]” CDs are compressed/limited to the point where they are clipped and they will “show red” in Audacity.

If the wave is clipped but the peaks don’t hit 0dB, Audacity won’t show red. For example, if you load a clipped file into Audacity and reduce the volume it will no longer show red. But of course, the wave is still clipped/distorted.

OK, thanks for the replies.

In short, if I understand it, red lines are ‘potential’ points of distortion. In odd places it is very unlikely to be noticed in normal listening environments. If there are too many points of red, say more red than blue, or if you are making audio tracks that require high end audio quality, then these red points would need to be addressed?

then these red points would need to be addressed?

I have a question about that.

If MP3 compression can go over 100% and I import an MP3 into Audacity whose internal format doesn’t overload, either, then who cares? I should be able to just bring the volume back down in Audacity and go make coffee.

No, I don’t expect that to actually happen because of other variables, but it could.

Do you know what the subjunctive is? Audacity clipping indicator works in the subjunctive. This sound would be distorted if it had gone over 100%. Since normal audio doesn’t ever go over 100%, we have to guess at it. Fuzzy memory tells me the tool works by sensing three consecutive digital samples at 100%. There’s no musical instrument that can make music like that so it must be distortion.

Some programs sense 99%. That is a very real number, but it’s not “100%” clipping. I’m not sure which is worse.

In any event, your sound should not spend a lot of time up there.