Clipping ?

[Pete C]

A few years ago 64 Guitars analysed one of my tracks on Audacity which showed a lot of clipping. Since then I've been more conscious of adjusting the recording level on my BR600 to avoid the clipping light showing, then I export my WAV file, normalise it in Audacity then save it as an MP3 file to upload to SC. This week I recorded Rockin in the Free World for the Neil Young fest. I exported the WAV file to my PC, imported it to Audacity which showed a little bit of clipping, normalised it, which showed no clipping, then saved it as an MP3 file and uploaded it. Tonight I was just playing about with Audacity and imported the MP3 file which showed a hell of a lot of clipping. When I normalised this the clipping disappeared. Question is after I've normalised the WAV file and saved it to MP3, should I be normalising the MP3 file too?  Hope you understand this !

Pete

[64Guitars]

Normalizing doesn't reduce clipping. It just optimizes the level. If the waveform is already clipped, it will still be clipped after you normalize. The only way to eliminate clipping is to keep the input levels low during recording. If the input level is too high, the tops of the waveforms will be flat instead of round. That's what causes the distortion. If you subsequently reduce the levels by normalizing, for example, the tops of the waveforms will still be flat (clipped).

To get good recording levels and no clipping, do the following.

• Pay close attention to your recording levels. Not just when mastering, but on each track too. If the level meters are hitting 0dB (the top segment) then you'll almost certainly have clipping. Reduce your recording level so that the top segment of the meter doesn't light. But don't set it too low. The second segment from the top should light occasionally.
• Export your finished song to a WAV file and load it into Audacity. If Audacity shows a lot of clipping, then there's nothing you can do in Audacity or any other program to fix it. The only way to fix it is to re-mix it with the levels lower. The same is true if the levels in Audacity are much too low. Normalizing isn't advisable for such a large level correction. Instead, you should re-mix with the levels higher But if the levels are only slightly low, then normalizing can be used to optimize them.

If you've made a good WAV file with no clipping, then exporting it to an MP3 file shouldn't introduce any clipping, in theory. However, the Audacity manual recommends that you normalize your WAV file to -1.0dB (rather than 0dB) before converting to MP3 just to play it safe.


By the way, the "Show Clipping" feature of Audacity is a bit of a misnomer. The red lines merely show samples that hit 0dB. But a single sample hitting 0bB isn't clipping. Clipping occurs when several consecutive samples all hit 0dB, forming a flat horizontal line. If you normalize a recording to 0dB, then some waveforms will hit 0dB at their highest point, but it will only be for one or two samples before it falls back down. There's no flat horizontal line, so there's no clipping. I downloaded your MP3 of "Rockin' in the Free World" and loaded it into Audacity. There are lots of red lines showing (especially in the left channel), but when I zoom in on them to see the individual samples, I see that there's no clipping. That tells me that you most likely normalized to 0dB. That's perfectly okay, but if you don't want to see all those red lines, you should normalize to a slightly lower level such as -0.1dB or, as the Audacity manual suggests, -1.0dB. That way, none of the samples will hit 0dB, so there will be no red lines.

Here's a small section of your MP3 where I've zoomed in on a red line to see the individual samples. You can see that only one sample is red (hitting 0dB). That's not clipping since it hasn't altered the normal shape of the waveform.



Now here's a zoomed-in section which I amplified by 6dB. Notice that there are many consecutive samples that are red, which results in a flat top of that section of the waveform. That's clipping because the waveform's normal shape has been changed. Instead of being curvy, it's completely flat in the red sections because multiple consecutive samples all have the exact same value (0dB) resulting in a flat (clipped) wavetop.

[Pete C]

Thanks 64 ! I really appreciate the time you take to explain technical issues and I know since your first explanation about levels a few years ago, I think the quality of my recordings has improved. Thinking back through how I recorded this I think I realise where I went wrong- I recorded the vocals last and had turned up the recording level but then left it at that same level when I bounced everything to the master track. The clipping on the left side must be the guitar track I'd panned to the left.  I'll pay a bit more attention to the levels next time !

Thanks again for your advice - I'm not too good with the technical side of recording so it's great to have someone here with so much knowledge!

Pete

[T.C. Elliott]

I've resorted to keeping my tracks at -6db peak on the BR box. Even then I still have spikes over. When I import into a DAW (I use reaper, but audacity would be the same) I lower the volume of the tracks to balance them out (instead of increasing the volume.)  I try to keep 5-6 db of headroom in the track. (So your master fader shouldn't peak above -5 or so.)  Then when I "normalize" or in my case, add some tube emulation/tape emulation, a limiter a very  small amount of reverb and a stereo spreader (sometimes) to the track I make sure it doesn't go over -.5 db from peak level. (Ideally it should be lower than that and recently I've decided to try to hit the -1 db if possible.)

In other words, keep your gain lower than you need. You can always limit it (normalize it) and raise it to where you want it. The bonus is, if you use plugins such as compressors etc., in your DAW, they work best when the track is at the optimal level which is usually well below -5 db.

As a side note, I duplicated a disc and sent it to the radio running around -.3 db from peak.  Radio stations compress their playback so it caused some problems. You need a minimum -.5 in order for radio stations not to make your music sound like ass when they play it. (Which is why I'm going to the -1db standard going forward.)

Welcome to the rabbit hole.

[Pete C]

Thanks for your advice too TC - I'll see how my next recording goes using the tips you've both provided.

Thanks again !

Pete

[IanR]

It is actually best to optimise the recording level of each track you record so that you don't need to normalise. When you normalise a track that is recorded too quietly, you are also raising the level of any background noise and hiss. My advice is to do a test run of the track you are recording and adjust the gain until you are getting the average level up around -6db. If you recording into a DAW it is easy to see the levels and adjust prior to recording.

Trial and error is the secret of learning good recording techniques. Having knowledgeable friends (like 64 Guitars) is also a great help and I agree that he has helped me too over the years.

[Pete C]

Thanks for your advice Ian. My recording set up is very simple - BR600 (which only has a red light that flashes if there's clipping), mixed down to the master track then exported to the PC where I convert to MP3. I added one extra step a few years ago at 64's suggestion which was to upload the .wav file to Audacity, check for clipping, normalise and trim the ends if necessary, then convert to MP3.  When it comes to using a DAW, it goes right over my head - I'd really need someone to sit with me and go through it step by step !
It took me ages to get to grips with the BR600 so I can't really see myself progessing beyond a multi-track recorder much as I would like to 

Pete

[IanR]

Hey Pete,

I hear you but DAWs can be easy. It depends what you  trying to do.

Audacity is a good simple DAW and can be configured to work with your recorder.

You can also get a free version of Sonar these days from Bandcamp. There are heaps of instructional videos on the web.

[Pete C]

Thanks Ian - it's something I'm going to have to look into. I've had my Boss BR600 for 12 years now and it's not going to last forever and there's not a lot of multi-trackers on the market these days.  I got a free copy of Cubase LE recently which came free with a Zoom G5N I bought but not managed to make much sense of it yet. I'll have a look at Sonar too - guess it's a case of getting out of my comfort zone and making an effort to learn to use a DAW.