Canon XH A1 meter not reading where the Sound Devices 302 says it should.

[John Whiteway]

Hello,

I've been having a bit of an ongoing problem. I've raised it here in this forum before. I was hoping someone might have the answer this time.

Here's the situation.

When I send tone from a Sound Devices 302 mixer to a canon XH A1 set to receive line level, I am able to fully open the camera's audio levels and get the reading of -20 dB, as is supposed to happen. Now I have 0db on the mixer matched to -20 on the camera. Problem is, with every test I do with real human voices, 0dB on the mixer corresponds to -12 db not -20. Something funny is happening here.

I was able to do a detailed test today. We were doing some interviews so I arranged to position myself by the side of the camera. From that position I could watch the camera's audio levels while watching those on the mixer as well. Throughout the interview, to keep the camera from going over -12 I had to keep the mixers meter reading below 0dB.

I've also tried connecting mixer to camera at mic level. Here again I set the camera pots to mixer tone such that 0dB tone on the mixer Vu equals -20 on the camera. When I do this the same phenomena occurs. In real life situations 0Db on the meter equals -12 on the camera not -20.

I've been trying for days to figure this one out. I'm now beginning to wonder if the anomaly isn't occurring somewhere in the camera for I've noticed something when setting the mixer to camera at mic level. In order to set the camera's two channel levels to -20 to match the 0dB tone coming from the mixer I have to place the camera's audio levels at different points. One channel is 4/9 open the other 2/9. That doesn't make sense.

Mind you, if there is something wrong with the camera's levels why does it correctly read -20 dB with pot fully open and tone coming from mixer line level.

I just can't figure where to go from here. As it is all I can do is let the meter ride between -8 and 0 to equal -20 to -12 on the camera.

Thanks.

John

[Steve House]

Originally Posted by John Whiteway

Hello,

I've been having a bit of an ongoing problem. I've raised it here in this forum before. I was hoping someone might have the answer this time.

Here's the situation.

When I send tone from a Sound Devices 302 mixer to a canon XH A1 set to receive line level, I am able to fully open the camera's audio levels and get the reading of -20 dB, as is supposed to happen. Now I have 0db on the mixer matched to -20 on the camera. Problem is, with every test I do with real human voices, 0dB on the mixer corresponds to -12 db not -20. Something funny is happening here.

I was able to do a detailed test today. We were doing some interviews so I arranged to position myself by the side of the camera. From that position I could watch the camera's audio levels while watching those on the mixer as well. Throughout the interview, to keep the camera from going over -12 I had to keep the mixers meter reading below 0dB.

I've also tried connecting mixer to camera at mic level. Here again I set the camera pots to mixer tone such that 0dB tone on the mixer Vu equals -20 on the camera. When I do this the same phenomena occurs. In real life situations 0Db on the meter equals -12 on the camera not -20.

I've been trying for days to figure this one out. I'm now beginning to wonder if the anomaly isn't occurring somewhere in the camera for I've noticed something when setting the mixer to camera at mic level. In order to set the camera's two channel levels to -20 to match the 0dB tone coming from the mixer I have to place the camera's audio levels at different points. One channel is 4/9 open the other 2/9. That doesn't make sense.

Mind you, if there is something wrong with the camera's levels why does it correctly read -20 dB with pot fully open and tone coming from mixer line level.

I just can't figure where to go from here. As it is all I can do is let the meter ride between -8 and 0 to equal -20 to -12 on the camera.

Thanks.

John

Just guessin but I believe what you're seeing is normal and aligning on tone at -20dB does not mean that voice peaks should also be at -20. I don't have one of those cameras to test and I can't find it in the downloaded manual but I suspect that the camera has a Peak Reading meter (PPM). Peak meters read, well, peak signal while VU meters respond to the average signal. Now with a pure sinewave tone, peak and average voltages are very close and the two meter types read the same. But with complex waveforms like the human voice the waveform peaks are quite a bit higher than the average levels and the 8db or so you're observing is by no means unusual.

You can set the ballisitics of the 302 meters to different types. Try this - set tone to 0VU on the 302 meter and in the camera to -20dB. Connect your microphone and set the 302 meter to its 'VU/Peak' combo scale. In the combo meter mode, there's a continuous line of lit LEDs up to the VU reading and then a dark gap up to a single illuminated LED representing the peak reading. Leave the camera levels set where they are for tone, adjust the mic levels so the VU reading for speech is 0VU. You'll note that the 302 Peak indicator is quite a bit higher than 0 and I'll bet the camera meter reading will roughly correspond to it.

[John Whiteway]

Hello Steve.

There is nothing, as you say, in the XH A1 manual that describes its metering system. It would, though, appear to be VU/Peak. When watching it at work there is a solid line of little bars that expands with volume, but above the hot end of this row there are two little bars that dance. These I’ve assumed are registering peak. The relationship between these two indicators appears to be similar to what I see when the 302 is set on VU/Peak. Unquestionably two things are being measured on the XH A1 meter.

In my experiments I’ve just been watching VU. In fact, I set the 302 at VU so as not to be distracted by peak. It’s here that 0dB on the mixer equaled -12dB on camera. I suspect that if I were to put the mixer meter on to VU/Peak I’d see peaks that match the peaks I see on the camera meter. I’ll conduct a test to verify that this is the case.

Thanks for the efforts to help. I’m beginning to feel that logical possible explanations are disappearing and am beginning to wonder if there isn’t possibly some malfunction in my camera’s metering system. I’m going nuts.

Thanks.

John

[Steve House]

Originally Posted by John Whiteway

Hello Steve.

There is nothing, as you say, in the XH A1 manual that describes its metering system. It would, though, appear to be VU/Peak. When watching it at work there is a solid line of little bars that expands with volume, but above the hot end of this row there are two little bars that dance. These I’ve assumed are registering peak. The relationship between these two indicators appears to be similar to what I see when the 302 is set on VU/Peak. Unquestionably two things are being measured on the XH A1 meter.

In my experiments I’ve just been watching VU. In fact, I set the 302 at VU so as not to be distracted by peak. It’s here that 0dB on the mixer equaled -12dB on camera. I suspect that if I were to put the mixer meter on to VU/Peak I’d see peaks that match the peaks I see on the camera meter. I’ll conduct a test to verify that this is the case.

Thanks for the efforts to help. I’m beginning to feel that logical possible explanations are disappearing and am beginning to wonder if there isn’t possibly some malfunction in my camera’s metering system. I’m going nuts.

Thanks.

John

Actually that's consistent with what I wrote. Voice at 0VU on the mixer when it's on VU mode should cause peaks in the camera to read about 8dB higher. Your mixer would then be indicating average signal while the camera is indicating peak.

[John Whiteway]

Just doing a few tests Steve. Never paid much attention to that pair of little bars that hover above the main read-out on the XH A1 audio meter before. Doesn't look like they are peak, or else maybe the meter is showing peak not VU. Just fooling around a bit now I see that they do not extend beyond what I've taken to be the camera's VU reading. If I talk and watch the meter what I see is that these two little bars stay at the top end of the display. If I stop talking and the main reading (the long bar of little bars) decays, for a few moments these two little bars stay at what was the bar's top end, then they decay too.

I've just posted a question about the camera's audio on the XH A1 section of this web forum. Hopefully someone will answer and explain to me exactly what is being measured on the camera's audio level.

Thanks again.

John

[Steve House]

Originally Posted by John Whiteway

Just doing a few tests Steve. Never paid much attention to that pair of little bars that hover above the main read-out on the XH A1 audio meter before. Doesn't look like they are peak, or else maybe the meter is showing peak not VU. Just fooling around a bit now I see that they do not extend beyond what I've taken to be the camera's VU reading. If I talk and watch the meter what I see is that these two little bars stay at the top end of the display. If I stop talking and the main reading (the long bar of little bars) decays, for a few moments these two little bars stay at what was the bar's top end, then they decay too.

I've just posted a question about the camera's audio on the XH A1 section of this web forum. Hopefully someone will answer and explain to me exactly what is being measured on the camera's audio level.

Thanks again.

John

They are a "peak hold" feature. Peaks are so quick you could easily miss 'em so the "hold" preserves the reading for a few seconds so you can actually see the sucker.

[John Whiteway]

Hello Steve.

Still waiting for verification as to what the XH A1 is measuring (I've raised that question in this forum and also contacted Canon).

I had always assumed it was VU but now I have my doubts. I've been reading what I can since I was last here and came across an article that says: "The majority of digital recorders... therefore use true peak reading meters whose displays are derived from the digital data stream." With that in mind and with your suggestions I've just tried another experiment. I set the 302 to read peak (ppm I think that's called) and then looked to see what readings I was getting from both the mixer and camera as I talked. They seemed identical. So it looks like you may be right!

If so, in a way, I should forget watching the camera. If I want a real pick-up of about -12 dB on the camera I should just trust the mixer - i.e. set it to +6/8 dB. The camera would likely now be reading about +6.

I tried this test on my Canon XL1 with the same results. It's funny. I used that camera for years always striving for -12 on its meter and was always very happy with what I got. If it turns out that both these cameras are displaying peak I guess I was actually recording at about -18 to -20 VU.

But I await confirmation from Canon or elsewhere about the nature of what the camera meters are displaying before I shout hoorah and finally declare my problem solved.

Thanks again.

John

[Steve House]

You don't ever want the camera to get up to 0 or full-scale. Anything over 0 and you're clipping, a big no-no. The idea of aligning is so you can watch the mixer meters and reliably infer what the camera is doing.

[John Whiteway]

Well at least that isn't a problem I've been facing. It the camera is displaying peak not VU I've been keeping peak at around -12 (VU somewhere around -18).

[Steve House]

Originally Posted by John Whiteway

Well at least that isn't a problem I've been facing. It the camera is displaying peak not VU I've been keeping peak at around -12 (VU somewhere around -18).

I don't know for sure but i'd be willing to bet money that the camera is a peak reading meter with a hold feature. As you said, if the continuous bar pushes the vertical line up with its upper end then drops back leaving the vertical line there for a moment or two before it too drops, then that's what you're working with. If on the way up there's a gap between the end of the continuous bar and the vertical line then it's likely a combination of VU & Peak.

[Petri Kaipiainen]

You should also have peak reading engaged on the SD302, then the readings should be identical on both the cam and the mixer.

If you have aligned the cam and SD302 like you should (and you have), pay no attention to camera meters. Set SD302 to show both VU and peak hold and use the exelent limiter. Then it is safe to ride the levels quite high (high is better, unless...) but next to impossible to get digital clipping on the camera. With fairly even dialog you do not need all that much headroom.

I have my limiter set at +17 dBVU on the mixer, that means a whooping 60 dB extra safety at the top with 1:20 ratio limiter SD302 has.

[John Whiteway]

Guess the mystery continues. I've just heard from Canon and they assure me the meter is displaying VU not peak. So here I am with VU readings on the camera that match peak readings on the 302 meter! So to which do I set my audio? To what the camera says or the meter??????

[John Whiteway]

Just spoke to the Sound Devices support people. They are thinking there may be a fault with the mixer. My assignment (if I understand them correctly): to get another tone generator, send it through the mixer and see if the mixer is reading it correctly. Any advice here on how to do that or what kind of tone generator I'm supposed to get?

As for what to do now - till the problem is isolated and sorted and based on us now knowing the camera is measuring VU not peak - the folks at Sound Devices say "the camera is God". Their advice is to match the mixer to the camera readings; that is, if 0dB reading on the mixer is equaling -12dB on the camera I should base my mixing on that.

Wow. What a (slow) lesson I'm getting in recording sound.

John