FCPX vu Volume vs Record volume on HD7

[John Nantz]

Just recorded some piano playing and while doing so I made a point to keep the volume levels below 0 db.

The rig was a HD7 camcorder with a Senheiser mic connected to a JuicedLink Pre. During the recording I watched the vu meter on the camera's flip-out screen to keep it in the vu meter green zone. It did go into the red zone very briefly before I turned the "pre" volume down a tad.

Upon uploading to the computer and playing the clip back, however, I found a number of areas where the FCPX vu meters showed the volume over 0 db. Attached is a couple screen shots showing the section of the clip where it not only went over 0 db but into the red zone. One can see little spots of red at the peaks of the volume in the audio channel. The FCPX volume meter also picked up the red peaks.

With the menu setting set for external mic the camera's vu readings are shown in the flip-out screen during the recording. However, when I looked through the HD7's Owners Manual I couldn't find anything about what the camera's vu meters read. The red area is pretty obvious but the Manual doesn't say at what db level the red shows up, or at least I didn't find anything.

If what FCPX shows, it appears that the red area is some distance above 0 db and 0 db must be one or two green bars below the red bars.

Question: Can anyone elaborate on their take of what the camera's vu meter is displaying?

Below is a couple screen shots of a FCPX where the audio is above 0 db (even though the camera was reading "green" and a part that is actually in the red). It is very possible that the camera's vu meter was reading "red" in that area as I was adjusting the gain on the "pre" as the clip was being recorded.

If so, and I think it is so, that would mean that 0 db on FCPX is probably a couple green bars below the red area on the camera's vu meter.

The vu meter reading is in the clip area but I couldn't capture a screen shot that would show where it was taken.

The 0 db line in FCPX is the horizontal line under the yellow spikes.

[Waldemar Winkler]

Hello, John,
If I get some time I'll send you a long update via PM.

Part of the reason for the peaks you are seeing in FCPX has to do with the fact that the HD7 doesn't allow you to set audio levels, even though you believe you are doing so with your pre-amp. The HD7 uses an auto gain system tied to a limiting circuit. If, for example, you turn down your pre-amp, the HD7's auto gain turns it back up. The limiter circuit is supposed to keep signals from going above "0" db in-camera under normal circumstances. That is when you see the audio meters go red. However, a condenser shotgun (powered by a battery) and a powered pre-amp is delivering a pretty strong audio signal to the camera ... perhaps a bit much for the limiter circuit to manage. I don't know if the audio limiter circuit is constantly updating its settings, or just locks onto the first audio sample it processes. I use a passive mic mixer (Sign Video), which may help.

However, we all have to keep in mind the camera's audio system was built for the built-in camera mic, not the add-ons we prefer to use. Another thing we have to remember is the strength of the audio signal is relative to the source and how far away it is from the mic.

In the end, when all is imported into FCP (I'm still on 7) it is rare for me to have the audio meters read below "0" db immediately after import. And, the purpose of the audio meters is to provide an average of all of the audio tracks on the timeline. Audio is additive. The more audio tracks, the louder the overall audio. One of the last, but not the last, things I do with a video project is balance all of the audio tracks with an eye to keep the average levels between -12 and -6 db, and allow no peaks to reach 0 db.

[John Nantz]

Originally Posted by Waldemar Winkler

If I get some time I'll send you a long update via PM.

Great! Sure, and work and making a living certainly comes first.

Originally Posted by Waldemar Winkler

Part of the reason for the peaks you are seeing in FCPX has to do with the fact that the HD7 doesn't allow you to set audio levels, even though you believe you are doing so with your pre-amp.... ... However, a condenser shotgun (powered by a battery) and a powered pre-amp is delivering a pretty strong audio signal to the camera ....

Would you believe, after all this time, I just discovered that the 9V battery in the JuicedLink Pre might be providing phantom power to the mic so I might not even need to have the 1.5V battery in the mic!

Then this begs the question, what is happening when both the pre and the mic are providing power? Guess I'll have to do some testing to figure this out.

What is a "passive mic mixer"? Something that doesn't provide phantom power? Or doesn't have gain controls? The Juiced Link has it's own gain controls, one for each channel, and I tried to find a good position for them. It is hard to do because one only gets to see the vu meter reading on the flip-out screen then the files have to be transfered to the computer to see how the audio went. Due to the time required then the recording settings have to be documented unless one has photographic memory.

Originally Posted by Waldemar Winkler

However, we all have to keep in mind the camera's audio system was built for the built-in camera mic, not the add-ons we prefer to use. Another thing we have to remember is the strength of the audio signal is relative to the source and how far away it is from the mic.

It's interesting that the camera's vu meters don't work when the camera's mic is being used. That's probably because one doesn't have any control over the volume. At least I've never seen where this is possible. One can manually control video brightness but apparently not audio volume.

Originally Posted by Waldemar Winkler

In the end, when all is imported into FCP (I'm still on 7) it is rare for me to have the audio meters read above "0" db immediately after import. And, the purpose of the audio meters is to provide an average of all of the audio tracks on the timeline. Audio is additive. The more audio tracks, the louder the overall audio. One of the last, but not the last, things I do with a video project is balance all of the audio tracks with an eye to keep the average levels between -12 and -6 db, and allow no peaks to reach 0 db.

Reading this makes me feel much better because that's exactly what happens to me (vu meters above "0" after import.

And that's the same thing I did when editing the audio was to put it in the range of -12 to -6 or even up to -~2 for the piano recording peaks. This range worked out very well for playback.

[Waldemar Winkler]

[Would you believe, after all this time, I just discovered that the 9V battery in the JuicedLink Pre might be providing phantom power to the mic so I might not even need to have the 1.5V battery in the mic!

Then this begs the question, what is happening when both the pre and the mic are providing power? Guess I'll have to do some testing to figure this out.]

You'll need something in the battery location to complete the circuit if your mic is to receive phantom power. I'm going to guess the mic will ignore phantom power when operating off of its own battery.

[What is a "passive mic mixer"? ] It doesn't require a power source. Mine is made by Sign Video, and is very similar to the first Beachteks. At full gain it passes the incoming audio signal through without modification. The two gain controls reduce the incoming signal strength. The output side (to the camera) is mic level impedance via a 3.5mm stereo plug. Somewhere in this forum is a post from a HD7 user who had figured out an approximation of db levels for the camera's VU meters. With the red marker being 0 db, each green dot is an approximate signal reduction of -3 db. I adapted a four conductor 3.5mm AV cable for headphone use by bypassing the video conductor in the plug. Really helps to identify distortion!

[It's interesting that the camera's vu meters don't work when the camera's mic is being used. That's probably because one doesn't have any control over the volume. At least I've never seen where this is possible. One can manually control video brightness but apparently not audio volume.]

I believe VU meters for an external audio source was simply an enhancement for the experienced video enthusiast. JVC probably assumed VU meters would be a confusing distraction for the average users, and therefore chose to not display them when the built-in mic was in use. The video brightness control in the menu is simply for the LCD screen to make operating the camera easier in low light situations. It has no effect upon the video recorded to the HD. However, if the camera is set to manual control, the LCD will display a very close approximation of the brightness level of the video being sent to the HD. Weird, huh?