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wave forms vs meters

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Craig Alan
wave forms vs meters
on Jun 20, 2014 at 10:47:10 pm

I thought if the audio wave form peaks were red, it indicates clipping, that is above zero. Yet I often find this is not the case. Can someone please enlighten me.

audio waveforms vs meters



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Bret Williams
Re: wave forms vs meters
on Jun 21, 2014 at 3:43:30 am

I think if you kept them discreet they would. IOW it's showing the tracks singularly and not taking into account any drop in level from panning, which would include making them dual mono.


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Jeff Markgraf
Re: wave forms vs meters
on Jun 21, 2014 at 8:14:32 am

I think what is happening is that FCP is respecting the typical -3dB drop in level when making a L+R output from, say, a mono source.

For instance, I have a stereo clip that I play in the browser. I make it a dual mono clip in the audio configuration. Played back in the browser, it is now a single mono channel. The two channels sum together, which raises the overall level by at least 3db. That waveform should track pretty consistently with what the meter shows. But when I cut that dual mono (but summed to a single channel) clip into the timeline, it's played back as a 2 channel output. The mono is split to left and right. Doing this on a real analogue mixer typically drops the level by 3dB to each output channel. So the meters read lower than the waveform.

If you've added any limiters or used the loudness function in the audio inspector, those effects are applied downstream of the source clip. So you could have a badly distorted clip (lots of red in the waveform) that plays out on the timeline (the meters) at a much lower level because of the limiting. Conversely, using a compressor, you could have a low level clip that plays out much louder from the timeline.

Make sense?


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Craig Alan
Re: wave forms vs meters
on Jun 21, 2014 at 6:45:00 pm

Thanks Jeff and Bret,

Keep thinking I get it, but not sure.

If only one mono channel is active on the timeline, does FC create a dual mono which is therefore an additive pair that looks like it is peaking on the waveform in the timeline but not on the output meters? Is that a fair summary of what you were both saying?

Our camera records to 4 channels.

We used an option to record the built-in stereo mike to channels 3 and 4. (there is no option to turn it off).

We are also using a 302 mixer and mixing two mike inputs to two outputs.

These were both calibrated to -20 from a 0 tone out from the 302.

Unless I want to mix in some room noise, I disable channels 3 and 4 in FC.

If two channels are active and set to four mono in the inspector then the two channels are mixed to dual mono and therefore even if one is peaking it is attenuated by the mix?

My sample below is set to four mono.

But we have only two of the mono channels active and they each have different waveforms.

The clipping in mono 2 on the timeline is not showing on the meters.

But if I select 2 stereo in the inspector then the two different channels do appear on the meters as well as the clipping. Can I assume this a matches what is happening on the timeline of no other filters are applied?

Should I care about clipping on the timeline channel if downstream I do not show clipping?

I also notice that I can deactivate any of the four channels on the timeline and in the inspector independent of each other. So will deactivation in the timeline mean the final recording does not include the deactivated channels or does the inspector's channel configuration determine this?

four mono sample



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Jeff Markgraf
Re: wave forms vs meters
on Jun 22, 2014 at 6:54:07 pm

Craig, audio in an NLE is always a bit of a moving target, so your confusion is perfectly understandable.

If only one mono channel is active on the timeline,

You can have one channel only in the browser, which will show up as a single channel in the meter display.
But the timeline (the "output" if you will) always created either a stereo output or a 5.1 output. So that mono clip, once placed in the timeline, becomes a stereo playback, albeit in dual mono. They key difference is that each channel of that stereo/dual mono output is now 3dB lower in level. Again, just like using the pan knobs on an analogue mixer. So a peak that shows on the clip's waveform will show up lower on the output meters.

But we have only two of the mono channels active and they each have different waveforms.

Maybe this will help clarify. Take look at your clip. For the purposes of this illustration, just deal with 2 channels of it. (turn off the other two channels in the inspector) If those two channels are set as a stereo pair, then when you play the clip in the browser, you will see two channels active in the meter bridge.

Now change your clip to dual mono (or 4 mono in your case, again leaving the other two channels turned off). The meter bridge now shows only one channel when you play the clip in the browser. That's because the two source channels are being summed to one mono channel.

If you now drop this mono clip into the timeline, you'll see it play back as a stereo output (i.e., 2 meter channels for left and right). And when the mono signal is sent to both left and right output to create that stereo output, the original mono signal is dropped by 3dB into each output channel in the process. Therefore, your 2 channels of the meter will show a slightly lower level compared to that mono channel from the mono browser display.


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Craig Alan
Re: wave forms vs meters
on Jun 23, 2014 at 12:14:28 am

I'm testing each one of your points.
Here's my results.

Playing a clip in the Browser:
I can display them in the inspector as either two stereo or four mono.
Four mono will play as a single channel on the meter display.
Two stereo will play as two channels on the meter display.
I can isolate any or all of the four channels by toggling the button boxes in the inspector at the start of each waveform.

Playing a clip in the Timeline:
One to four mono will play as two identical channels on the meter display, not like in the Browser.
Stereo will play as a pair, same as in the Browser.

I get the 3 dB drop in level when two mono channels (L and R) are panned to center and I tried panning to the right and left 100% and sure enough the peaks that clipped in the timeline peaked on the meter display.

So I think I get the audio part of things. What has me still confused is the relationship between the Inspector's toggle boxes for the Inspector's waveforms and using the V key to deactivate an expanded "track" of audio in the timeline.

Timeline Audio Clip Expanded:

When I uncheck a channel in the Inspector, it disappears in the timeline.
Not just turns a lighter grey and deactivates, but literally goes away.

A deactivated (V) audio channel in the Timeline remains deactivated even if it is checked in the Inspector.

Not sure from this inconsistent relationship what the best practice is or how it will effect the final export of a finished project.

Hopefully if the channel of audio is either disabled or made invisible that it will not play or export with the project. But why the different behaviors? Why not just grey it out when unchecked in the Inspector and if it is disabled in the Timeline, uncheck it in the Inspector?

Is there technically any difference in the audio file if the channel is muted (disabled) but still visible in the Timeline?

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Jeff Markgraf
Re: wave forms vs meters
on Jun 23, 2014 at 1:24:21 am

Hi Craig.

get the 3 dB drop in level when two mono channels (L and R) are panned to center

Pretty sure you mean 3 dB drop when each mono channel panned to left or right. Both panned center sums them and increases the volume.

the relationship between the Inspector's toggle boxes for the Inspector's waveforms and using the V key to deactivate an expanded "track" of audio in the timeline.


Picture an old-school edit system with a source deck and a record deck. Think of your clip in the browser as a source tape with 4 channels of audio recorded on it. When the browser clip is active, the inspector audio controls are kind of like the output controls of the source tape deck. If you turn off a channel in the inspector, it's like turning the volume control all the way down on the deck output. It's still patched to the "record machine" - i.e.. the timeline. But there's nothing being sent.

When your clip is actually in the timeline and selected, the channel controls in the inspector are controlling the "record machine" levels and patching (actually more like a combination of the audio board and the record deck inputs and outputs). If all 4 channels are active, it's like making an audio insert edit with all 4 audio channels armed. If you turn off a channel in the inspector, it's like disarming that channel on the record deck. It will only make the audio edit to the 3 armed channels. That's why it disappears in the timeline - you've turned off, or disarmed, the record channel.

Keep in mind that you can only monitor the record deck (timeline) as a stereo output. So if you have stereo on 1&2 and on 3&4, they're combined into one stereo output. Any mono tracks that are panned center show up on both 1&2.

Using the v command to deactivate the channel in the timeline is like playing back your edit, but not feeding that channel to the record deck's stereo output monitor. It's still on the "record tape" but not heard.

Hope that makes sense.

Coming from a linear online background with limited audio channels, I have always put only the audio I actually need into the timeline. So if my source has both lav and boom, I'll just put the preferred source in the edited timeline. No need to use another track for audio that will just get turned off in the mix. But many people I know who grew up on Avid, etc., place all the audio in the timeline and let the mixer sort it out. I find that approach cumbersome and wasteful of time and resources. But to each his own.

As far as FCPX best practices, my understanding is as follows: if an audio channel is in the timeline but deactivated, it will still be included in the XML. Therefore, it will be included in an X to Pro file for use in Pro Tools, etc. It will also be included in the roles-based export, I think, but I'm not sure it it will be "live" or not. If the track is turned off in the inspector, causing it to disappear from the timeline, it's gone and will not appear in the XML or any other export. This would be my preferred method.


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Jeff Markgraf
Re: wave forms vs meters
on Jun 22, 2014 at 7:40:39 pm

A couple more thoughts...

Let's be sure we're talking about the same thing when we say "clipping."

These were both calibrated to -20 from a 0 tone out from the 302.

Yell at me it this gets pedantic... the -20 = 0 VU sounds just right. (I recall some decks, like DigiBeta, used -18, but same principle...) Translated into FCP7 workflow, that -20 tone equalled -12 on the FCP output meters. This all kind of assumes that the top of the green = 0VU, with the yellow and red following logically as OK peaking followed by clipping at +6 (or potential clipping, since digital will really only "clip" at more than full swing).

So on FCPX, do we apply the same levels? Does a single channel of -20 tone in fact show as -12 when you play that single channel in the browser? If so, then there's a good 18dB of headroom available, as the meters again show +6 as the top level. The waveform showing yellow is not clipping, merely peaking appropriately above the "0VU" reference.

It seems logical to take the red in the waveform as 0dB, or peak level. Certainly the top of the meters in the output should be considered a true peak output. So I would actually interpret the red peak indicator as full swing digital signal, no clipping per se. In other words, still too loud, but not necessarily clipped (as in truncating bits). Since we'll never see "more red than red," it's sensible to take the 0dB peak indicators as actual clipping for practical purposes.

I think the bottom line is that the waveforms should be taken only as a loose reference level. I just looked at a cut from a commercial CD. These CDs are typically very compressed and use every bit of the digital signal available. The waveform in the browser shows solid red across the top of the waveform in the single clip view (but no red in the multiple clip view). Played back in stereo from the browser, with no level adjustment, it looks on the meters just as I would expect: pretty much slammed at the "0" mark. 12 dB above the reference -12 tone level, with 6dB of headroom going completely unused. So no clipping going on, just really hot, compressed music. Yet if I look at the waveform in the browser, I would have expected clipped, distorted playback.

Ergo, the waveforms are not to be taken literally. Trust the meters, based on the reference levels appropriate for your application. If you have access to an outboard meter, such as the Dorroughs, by all means use it for real accuracy. Perhaps borrow or rent one, and compare to the FCP meters so you know how well they track (or don't track).


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Craig Alan
Re: wave forms vs meters
on Jun 23, 2014 at 1:09:46 am

[Jeff Markgraf] "Translated into FCP7 workflow, that -20 tone equalled -12 on the FCP output meters."

Somehow this must be related to the -12 mark on consumer level cams that don't even have the -20 marker?

I have never read a good explanation of mixer to camera to NLE in terms of the different meters. Except that 0 out mixer equals -20 on any pro camera (recorder). I follow the rule without truly understanding it. I've also learned that you have to get used to your camera in terms of where on its meter it starts to sound distorted. Or even, where the sweet range is.

You really have to trust your ears as much as the levels. You start to learn where to aim as you listen.

[Jeff Markgraf] "It seems logical to take the red in the waveform as 0dB, or peak level."

I look at 0 on FC's meters as being the audio equivalent of 100 on a histogram scope for highlight levels. The whites get crushed. The sound starts to distort or even just too loud given the rest of the audio track levels. On my sound devices mixer we can get away with the meter's clip light coming on for a split second because there is a built in limiter. But you don't want it there if you can avoid it.

[Jeff Markgraf] "Yet if I look at the waveform in the browser, I would have expected clipped, distorted playback. "

Well this sounds exactly like my original question. If it's evenly slammed against the limit I'd guess they used a filter/limiter to prevent any clipping. I used to use that broadcast safe filter/audio limiter in legacy FCP. I could edit using my ears and meters and then apply these filters to just be sure. But I was really just following advice, not really getting it on a higher level. I do know as a consumer that some movies are crystal clear and easy to listen to and others I miss lines in every scene.

I have noticed that when we import music from a pro recording, yeah it's in the red in the timeline and on the meters and is just too loud in terms of the rest of our sound. Not sure what to make of that. But it's pretty easy to adjust and get good levels because it was recorded well to begin with. The cleaner the recording the more you can lower the levels and still be able to hear it clearly.

[Jeff Markgraf] "If you have access to an outboard meter, such as the Dorroughs, by all means use it"

Where would you hook this up? To the computer's audio out? I assume a pro audio app would have better metering than FC? They seem to have a whole range of these meters at different price points. Which is rec. for audio editing?

Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Jeff Markgraf
Re: wave forms vs meters
on Jun 23, 2014 at 1:59:18 am

Hi again Craig.

When it comes to consumer cameras, all bets are off. They all have some kind of limiting, often compression as well. None can generate a tone, so there's no absolute reference. That's why they're really only good for a guide track or run-and-gun shooting. Recording a stereo audio track is consumer nonsense, and that audio should be made dual mono in the editor and dealt with accordingly, IMHO.

A major point of confusion is the "0" reference. 0VU is completely different from 0dB. The 0VU (stands for "volume unit") is an old term. If you consider an audio signal to go from 0 to 1 volt, the 0VU represents something like 75% of the voltage, taken as an average RMS measurement. It's an electrical test signal, not unlike color bars. The trick has always been knowing 0VU referenced to what absolute level, expressed in dB or dBF. Pro gear referenced to +4, while consumer electronics referenced to -10. The "0" on the left side of the FCPX meter is kinda like 0VU.

0dB is an actual measurement of loudness. From a few dB for a whisper to over 120 dB for a jet engine. It's a logarithmic scale, so an increase of 3dB roughly equals double the "loudness." In fact, most people can't reliably detect a difference in loudness in increments less than 3dB.

So in digital land, like an NLE, the very top of the scale is 0dB - no attenuation of the signal. The reference tone at -20 is 20dB of attenuation of the full swing signal. For metering purposes, the test is referenced to the 0VU level - or maybe the other way around.

The goal in analogue was to keep the signal high enough to be out of the noise floor, but low enough to avoid distortion. Analogue distorts in a gradual way, so you really had to know wheat kind of sound you were looking for. Some classic pop albums had a deliberately applied bit of distortion, saturating the tape and electronics.

Digital doesn't distort until it clips. Nothing subtle about it. But we still need a reference level, below the clipping level, that is our baseline and has plenty of headroom available before clipping.

Just like looking at a video signal on a waveform monitor (or histogram, if you prefer that methods). The 1 volt video signal contains the 0-100 IRE useable area of the signal, plus some headroom (to about 115 IRE) and room at the bottom for the synch (-40 IRE). You are correct that 0dB is like the very top of the measured signal, where it crushes. That's the point in digital where bits are actually lost. You'd never shoot or color correct to force the majority of your picture up into the top 10 or 20% of the range. Just like you'd never crush everything toward black. That 0VU tone is kind of like the 60 to 70 percent level where flesh tones (based on brightness) look good. There should be plenty of peaks above that level, just not too far above it.


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Craig Alan
Re: wave forms vs meters
on Jun 23, 2014 at 4:18:50 am

On the mixer I use the output level of the tone oscillator is in dBu at LINE level. 0 dBu.

As for color correcting exposure (Luma levels). I try to keep my deepest blacks a hair above 0 and the brightest highlights a hair below 100 with the widest dynamic range as possible. Then I play with mid tones which includes human skin tones to create a look. Then I might color correct I'm terms of hue and saturation. Then I recheck the overall Luma levels.

I understand that digital audio doesn't clip until it does. So maybe distortion is the wrong term. But I do know that I can find the sweet range on even a consumer level camera. And some are better than others and they are all helped by using a mixer. Though you can't bypass the cam's poor preamp altogether, you can keep it turned down and rely more on the quiet preamp of a good mixer. However there is no exact way to calibrate the mixer to a camera that does not allow for -20 calibration. I know, for example, on the Canon HV40s That 0 tone out the mixer works pretty well if you calibrate at -12 or a bit lower. And also if you keep the mixer peaks to about +4. This gives you extra headroom. I also find it depends on the mike being used, how close to the source, and again monitoring with headphones.

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Jeff Markgraf
Re: wave forms vs meters
on Jun 23, 2014 at 2:46:40 am

More. Isn't this fun?

I have noticed that when we import music from a pro recording, yeah it's in the red in the timeline and on the meters and is just too loud in terms of the rest of our sound. Not sure what to make of that.

It's an artifact of the loudness wars that began decades age on the radio. Louder was perceived as better and more likely to catch the casual listener's ear. This phenomenon is generally limited to pop music. Classical and Jazz CDs have normal levels. Symphonic music, in particular, needs lots of headroom, so the average levels are much lower.

some movies are crystal clear and easy to listen to and others I miss lines in every scene.

All depends on the mixer. And on where you see the movie. Theatrical dubbing stages are very rigorously set up to a well-defined standard. They don't turn the monitor up or down. The system has a peak output level that you work with. So the average level is well below the peaks, and can often get very quiet. Movies are also mixed in at least 5.1 surround. If you watch at home, especially on a stereo mix derived from the original 5.1 mix, levels can be all over the place. Dialogue that sounds plenty loud and crystal clear on left/right/center playback in a theatre can sometimes all but disappear when the surround mix is folded into simple L/R stereo. That's why movies have to be remixed for TV. They are severely compressed and the dialogue is boosted. Listen sometime to a live music event (like the Grammys or the Tonys or an awards show) to see how well the 5.1 mix being done in the truck translates to your run-of-the-mill stereo TV set at home. Often, it's a mess.

Where would you hook this up? To the computer's audio out?

Depends on your system. Do you have a proper broadcast monitor fed by an AJA or Blackmagic card? If so, feed it with the SDI signal and it will be disembedded. Your monitor may already have audio meters built in (like my Flanders Scientific). Otherwise, the AES output from your video card goes to the outboard meters. Coming directly out of the computer is dicey if it's a line out or headphone out, as there's no true reference level. A USB out to a mixer or metering bridge may be an option, but it has to bypass any computer output volume control.


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Craig Alan
Re: wave forms vs meters
on Jun 23, 2014 at 5:20:59 am

Jeff this has been very helpful and I appreciate it.

I actually do have a Flanders monitor with a Black magic card which I use for color correction. I'm disappointed that I can't use it for Aperture. Or monitoring QT movies after exporting them.

Didn't occur to me that it would be helpful for audio as well. Are the audio meters on the Flanders of good quality? I love it for the visual features.

I am connected to the black magic card on SDI 1.

How do I bring up the audio meters on the Flanders. I have LM-2140W.

I can call Flanders tomorrow if need be.

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Jeff Markgraf
Re: wave forms vs meters
on Jun 23, 2014 at 6:00:58 am

Not at my system now, but it's in the menu. My preset #3, I think, has the audio meters along with a histogram. I went into the menu, meters, audio and changed the audio display from the default 12 or something channels to just 1& 2. I also turned off the histogram. So it's just 2 vertical meters in a grey overlay. On mine, there are convenient markers at the -18 level and at the -6 level. Pretty handy. Fast rise and slow decay, just like the pros! I would trust them more that the FCPX meters.


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Craig Alan
Re: wave forms vs meters
on Jun 23, 2014 at 6:29:38 am

Well I got the meters to display two channels but not sure how to turn off histogram. I think I'll call customer support and have a tech guy talk me through the menu system.

But nothing is registering on the meters. Maybe a FCP preference?

The meters read from -60 to -10?

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Noam Osband
Re: wave forms vs meters
on Sep 25, 2015 at 7:11:24 pm

I've been doing more audio editing with FCP X and I got to Creative Cow to look up this precise question, why it might be read in the timeline waveform but not clipping in the audio meters.

I'll be honest....I read the thread and it seems like there is no answer, other than the fact that perhaps there is a limiter that leads the timeline waveform to go red while my meters don't clip.

I guess I'm asking for the bottom line from those who would know better: should i ignore the timeline waveforms and just go by the audio meters? I'm using good headphones and it doesn't seem to be clipping in those cases when the meter is good but the waveform is red.


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Craig Alan
Re: wave forms vs meters
on Sep 26, 2015 at 5:15:41 pm

Yes use the meters for actual levels but the wave forms allow you to
Key frame small increments of adjustments. That is right click on volume bar and key frame it. Then use range tool to select the adjusted area and click the ? Key to play the selection only while you watch the meters and listen while th headphones. Seems like Fcp x is all about using different windows at once

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Noam Osband
Re: wave forms vs meters
on Sep 26, 2015 at 5:20:24 pm

I guess what's weird is that it seems the colored waveforms are useless then, right? What's the point of them?


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Craig Alan
Re: wave forms vs meters
on Sep 26, 2015 at 10:16:54 pm
Last Edited By Craig Alan on Sep 29, 2015 at 7:21:04 pm

well the waveforms in general do indicate the relative volumes within a clip but the absolute levels are indicated by the meters. I wouldn't mind all that if they would add a feature to normalize and/or add a limiter and or broadcast safe filter (vocab?) to the entire timeline or selected portion.

Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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