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TOPIC: Need some help understanding audio waveforms

Need some help understanding audio waveforms 24 Mar 2020 13:54 #105562

  • bryanfowler
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Yeah, I know.. understanding waveforms?! Dude... =)

What I'm having problems understanding is how they show up visually in the timeline. And why it seems different from the meters, and what I'm hearing.

I have a public speaker talking. I've added compressor to him, brought things up to peaking around -6, and the audio waveform on the timeline is half red. If I believed the timeline it looks like the audio would be clipping. but in the meters it's not. It's bouncing right around -6

I know I could just ignore that, and go by how it sounds but if I could understand it a little that might help.

there is no gain added on the clip, Only plugin is the VO enhancement fx, with compressor, de-esser and EQ

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Need some help understanding audio waveforms 25 Mar 2020 11:50 #105599

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Compressors often add gain to the audio.

I feel you are over-thinking the timeline waveforms. They are representations so you can see when folks are speaking individual words, they're not a substitute for meters. They, by their nature, can't be that precise. Watch the meters for levels, not the waveforms. The waveforms seem to go red below 0db, around -6db, like where broadcast likes audio to be at.

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Need some help understanding audio waveforms 25 Mar 2020 17:30 #105615

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Hello, I'm an audio guy and I absolutely love the way FCPX handles waveforms. Bryanfolwer is right, the waveform will show red long before the meter hits red. I also believe this is on purpose because broadcast levels are lower than 0db. However, I do not produce programs for broadcast, I produce for streaming where the volume war is alive and well. I use the lovely compressors that are downloaded with Logic Pro X with the built-in limiter. I first set the limiter to my desired maximum output, usually -6 or -3. I then use the compressor with its makeup gain until I see the limiter indicate gain reduction. All the time I am watching the waveforms change in real-time showing how my compressor and limiter are effecting the audio levels.

I hope this helps.

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Need some help understanding audio waveforms 26 Mar 2020 13:19 #105635

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Thanks for the replies.

Just a couple of points.
I'm not using the waveforms as a substitute for meters.

However I am using them as an indicator of when the levels would be hot enough to clip. i.e. turn red on the timeline. That's not just arbitrary programming. If it's red on the timeline, that's designed to be telling me something. What is it telling me?

The waveforms seem to go red below 0db, around -6db, like where broadcast likes audio to be at.

Sounds like FCPX.guru is telling me that they don't match on your timeline either? And by match, I'm assuming that yellow means almost clipping, and red means clipping.

That's good to know. Still confusing, but nice to know that it's a similar experience.

On my timeline now is someone speaking, a loud section shows yellow, and that's about -10db on the meters (which is what I'm using as a reference, not the timeline.

I've been on FCPX since it didn't allow external monitors. Stepped away for a while and now back editing some while the world cleans their houses.

Sounds like BuckoBell and I have a similar lineup. Right now I have compressor, dresser (hardly on), EQ, noise reduction. It's sounding great, peaking around -6. Thanks Bucko for the reply.

Happy editing 'y'all.

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Need some help understanding audio waveforms 27 Mar 2020 14:00 #105686

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Again, the waveform in timeline goes red at -6db, which is super handy for us doing TV broadcast. That's all there is to it.

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Need some help understanding audio waveforms 28 Mar 2020 00:10 #105696

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What I notice though when looking at the waveform turning yellow and red is that this only applies to the SOURCE level!

Do a simple test: Take an audio clip put into a project (timeline). If it is recorded by professional gear which normally operates with -10 as normal and -9 to 0 as headroom, you'll see first yellow and then red for all levels above -10. Now set the level so you have no yellow or red peaks.
Then Compound that clip and apply a compressor (maybe choose 'rock vocal compressor'). What you'll see now is that the red only shows on the waveform when you actually hit 0, or close to it.

What I take from this is that the colouring of the waveform tells you whether the original audio of a clip is set to the correct levels, meaning -10 as normal max
OR
a compound clip (which behaves like a bus in a traditional mixer) is above 0dB

Another good example to demonstrate that the colouring only applies to individual clips and NOT to the sum of the master is if you place 2 clips on top of each other that individuals are set to not show yellow or red, but when you play both at once looking at your meters you'll see the sum of both now is higher than -10.

So colouring applies to individual clips, meters always to your combined master level.
What I haven't fully explored is how multichannel mono track clips behave. Maybe time to read up in the manual about how audio is processed :-)

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Need some help understanding audio waveforms 28 Mar 2020 20:56 #105705

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Hi Bryan Welcome to the fcp.co forums
Going back to basics, the waveforms shown for the individual clips is a representation of the original audio recording including how "hot" it was recorded at, and certain effects added to the clip itself, ie adding gain will boost the waveforms. Other sound effects may be added as connected clips and will not change the clips waveform.

From Apple's own words, when the waveform shows Red that is 0dBFS not -6dB. (Sorry Ben)

1 In Final Cut Pro, select the clip in the timeline.
2 Adjust the volume, and play back the clip again to test for peaks.
In the timeline and browser, the waveform section or sections of a clip turn yellow when a level is approaching peak levels, and red when a level exceeds 0 dB.
This is included in several Apple documents including the User Manual

So where does the -6dB come from, it comes from how FCPX applies Pan Law to clips and passes it to the Master output. FCPX almost always (but not always:(. ) attenuates the audio by -6dB. So it is entirely possible for the clip waveform to show red, but not the Meters. So it is easy to see why Ben and others think Red means -6dB not the actual 0dB as Apple states.
I would like FCPX to allow users to set this in preferences and that the default be -3dB so it corresponds to Logic Pro's settings. If you use ProTools, you may find -9dB as PT applies -3dBs to final export, then FCPX applies another -6dB.

There are many other reasons that the waveforms do not correspond directly to the Meters. This includes how the algorithms are applied using a Floating Point Math calculations, the amount of actual headroom Apple leaves by default ~+6dB and several other factors. By all logic, a digital signal should be just garbage anytime a Red waveform shows up or the Meter peaks above 0dB. This is not the case for Apple, but is for some other DAWs and plug-ins where 0dB is the absolute highest you can go period without some form of distortion or pop. You do not want to digitally record in the Red, but in analog recordings especially to tape, you often push the VU meter to the 0 and beyond to saturate the tape.

Solution is simple, just watch your Meters, set below 0dB. How far below depends on where delivery is going to be. Adding EQ/compressor/limiter to final output can ensure output volume. If you see lots of red in clip waveform, I would lower the overall volume and "Range" select individual red peaks and attenuate just the peaks so that I have more headroom for the entire mix.

There are new standards like in Europe, and for broadcasting the actual specs change. Speaking of delivery and broadcasting, LUFS standards are now a thing and can be seen as a diagnostic tool for "perceived" volume and overall range as it adds in analysis of frequencies and stops some of the outrageous manipulations for commercials as an example. YEA! You can create audio that sounds louder to listeners by jacking up certain frequencies that humans hear well, but the actual dBs do not change allowing it to pass "Loudness standards".
Ok last link is to an article by T. Payton, a forum contributor, on Apple's application of Pan Law which he thinks is a bad bug…
tpayton.com/the-pan-law-fcpx/

Happy Editing
Hope this Helps, Greg

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Need some help understanding audio waveforms 28 Mar 2020 23:46 #105706

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"From Apple's own words, when the waveform shows Red that is 0dBFS not -6dB. (Sorry Ben)"

I'm telling you what actually happens on my timelines. I don't care what Apple claims, I care about what I physically see on my timeline. And it hits red in the Timeline when the meters hit -6db. Fact. If Apple wants to excuse this away with Pan Law, good for them. But the fact is that when my meters hit -6db, the Timelie shows red.

And since the CALM act in the U.S. why has Apple ignored LUFS meters?

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Last edit: by FCPX.guru.

Need some help understanding audio waveforms 29 Mar 2020 00:08 #105707

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"FCPX almost always (but not always:(. ) attenuates the audio by -6dB. So it is entirely possible for the clip waveform to show red, but not the Meters."

Is this documented anywhere?

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Need some help understanding audio waveforms 29 Mar 2020 15:27 #105717

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Hi Ben
If you do not believe Apple's own documentation… "
"From Apple's own words, when the waveform shows Red that is 0dBFS not -6dB. (Sorry Ben)"
(copied directly out of the FCPX 10.4.7 user manual)

""I'm telling you what actually happens on my timelines. I don't care what Apple claims, I care about what I physically see on my timeline. And it hits red in the Timeline when the meters hit -6db.""

I honestly do not know what documentation would be acceptable to you if you are not willing to except Apple's own. A simple internet search will result in thousands of hits about this subject and YouTube has many tests showing this using tones and other audio inputs. Please go have a look including the link to T. Payton.

I did not go into all the details like stereo project vs mono/dual mono sources, surround sound etc… because it is not what the OP asked, but he did ask why it shows up as it does and I believe that the -6dB cut is mostly the answer he seeks. I also provided a brief explanation of how I would deal with red clip waveforms. In fact this advice mostly agrees with your advice to ignore the "red" and monitor the Meters. I do believe that he should lower volume in clip below red waveforms to provide more headroom so I included that advice.

Ben I do not want this to become a war of opinions, so please go study the issue, read the documentation and watch the testing that "proves(IMHO)" this is in fact what is happening. It answers why you are seeing the Meters as you are! For a person in your professional position, this could be important to understand correctly!

I faced this long ago when I switched to Logic Pro and later discovered the preference in LP that allows you to set the Pan Law compensation to 0dB or -3dB. Wish this preference was included in FCPX; user controlled and only -3dB, which I find better for my needs.

Happy Editing
Greg

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Need some help understanding audio waveforms 29 Mar 2020 23:40 #105723

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I'm not expressing an opinion, I'm telling you what factually happens physically in my edits, that's all. But you said I was mistaken, what I actually experience isn't true. So, that's all. I know what I do daily, and how it behaves for my work, daily, that's all. No documentation can make me believe I'm hallucinating.

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