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pads and volt meters

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Craig Alan
pads and volt meters
on Mar 8, 2008 at 6:41:25 am

I often run feeds from different sources with somewhat inconsistent results. I'm using a shure portable mixer between the house boards/powered speakers with line outputs, etc. and my cameras. I'm careful about matching line level out line level in or mic out mic in but the signal strength is inconsistent. What I'd like to do is get a volt meter and some pads so I can know what I'm dealing with and pad it to the proper level. Any recommendations about how best to do this?

What's the right device to use to measure the signal? Should I add an extra short xlr cord to one side of the pad or plug directly into the mixer? Are the variable pads good or just get a few different ones 10/15/20?



OSX 10.4.11; Quicksilver Dual 1 gig; G5 dual 2.5 gig; FCP 4.5, 3.0.4; Sony camcorder vx2000/pd170;Canon xl2; Pana consumer cams; write professionally for a variety of media;teach video production in L.A.


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David Jones
Re: pads and volt meters
on Mar 8, 2008 at 7:06:32 pm

This is one of those issues I (as a production sound mixer, and not a sound renforcement guy) have had to deal with all to often. Anyway, if the source you're getting from the house feed is from microphones, then the house feed (to you) should be a mic level. If it's not, see if it can be changed (from the house board). If it can't, then set your mixer to line level; you shouldn't need to insert a pad from the house feed, if it's set up correctly. I don't know what model mixer you have, but it should have pads built into it that you can switch between (usually 0 or no pad, -10 and -20).


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Craig Alan
Re: pads and volt meters
on Mar 9, 2008 at 9:49:49 am

I'm using the Shure FP33. I went so far as to email the company and ask how to engage an internal pad to the Shure's own output. Line out the Shure is +4, which is a bit too hot for the pd170s. Basically it was recommended to use external pads. The house board probably can be adjusted but so far the crew does not know how. Using the house board I get pretty good results with line out/line into the Shure/line into my cameras. But it is a bit over modulated. Using a line out of powered speakers, I see no choices. Mic level into the Shure is distorted. Line in gives fairly clean sound but is weak. Even though the camera's meters indicate a strong signal, the final captured sound is too low. It sounds fine when monitoring with headphones but when we play it back on a television, the volume is low.

I'd really like a way to measure the level coming out of these sources.

OSX 10.4.11; Quicksilver Dual 1 gig; G5 dual 2.5 gig; FCP 4.5, 3.0.4; Sony camcorder vx2000/pd170;Canon xl2; Pana consumer cams; write professionally for a variety of media;teach video production in L.A.


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Ty Ford
Re: pads and volt meters
on Mar 9, 2008 at 12:55:45 pm

Hello Craig and welcome to the Cow Audio Forum,

Couple of questions. When you say the FP 33 is too hot for your PD170, how are you calibrating the two?

The FP33 manual says begin tone and set the master for a 0 VU reading, then adjust your camera audio input controls.

The FP 33 manual also says clipping occurs at +18 dB on the mixer and that you can set the limiter from 0 to +17 dB.

Call me crazy, but here's what I'd try if I had your rig here.

Set the limiter threshold of the FP33 at +14 dB.

Set tone on your camera with the mixer master set at 0 VU. Now, DON'T CHANGE THE MASTER. Leave it at 0 VU.

Adjust your camera audio inputs to -18 for the tone.

With this calibration, I "THINK", you'll run out of headroom on both the mixer and the camera at the same place. And, setting a +14 threshold for the mixer's limiter will knock down the audio to the camera a bit more. Some limiters sound better than others. Shure's on the later models sound OK. But I haven't heard an FP33 in a long while.

Some sounds like hand claps, tongue clicks, three-ring binder opens and closes, etc., will probably sneak through the limiter. By setting the threshold at + 14, you still have another 4 dB as a safety net before the mixer clips at +18 dB.

To find out if the limiter sounds OK, after setup, stick a boom mic right in your face and talk. Turn it's channel up enough light the limiter light. Also check the camera meters to see if they are OK. If it all works as I THINK it might, the limiter will catch the peaks, the camera inputs won't go into distortion and you'll get a chance to hear how good or bad the FP33 limiters sound. (I tickle the limiters on my Sound Devices 442 and those limiters sound very good.)

Your VU meters may be pegging, but more importantly, watch the peak meters on the mixer, listen to the audio and watch what happens at your camera input meters. Your big concern is not VU level, it's what the peaks are doing.

Let me know if you try this and what the results are.

Regards,

Ty Ford



Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Craig Alan
Re: pads and volt meters
on Mar 9, 2008 at 7:16:04 pm

Hi Ty,

Thanks for your help.


Yes I begin tone and set the master for a 0 VU reading, then adjust my camera audio input controls.
And the results are pretty decent but varies depending on what is fed into the Shure. And the signal is too hot so that a speaker talking into a hand held mike, for example, can easily overmodulate by raising their voice. Yes we have an audio person assigned to watch the level and adjust. But line out is +4 and the pd170 should recieve a -10 (about, line signal).

Yes the instructions talk about setting output limiters. But read the section on how this is done. This is how I got started emailing the company about how to do this.

"Connect a 600 􀀺 load and an ac voltmeter across the
Left Line output as described in steps 1 and 2 of the
VU Meter Adjustment procedure." etc.

I have no idea how to do this. When they wrote back they suggested using external pads as if these instructions were not meant for end users. Here are some quotes from Shure.


1) Do you have the FP33 User Guide? (VU calibration instructions on in the User Adjustment Guide)

2) The VU meter adjustment may not the range to reach 0VU = -10dBm

3) A simpler method is to keep the FP33 at 0VU = +4dBM, then add a 15 dB pad after the FP33 line level output.

You can't re-calibrate the vu meters with out the required equipment.

Lets make this simple. Just adjust the channel and master volume controls so the vu meters read -10.

OSX 10.4.11; Quicksilver Dual 1 gig; G5 dual 2.5 gig; FCP 4.5, 3.0.4; Sony camcorder vx2000/pd170;Canon xl2; Pana consumer cams; write professionally for a variety of media;teach video production in L.A.


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Ty Ford
Re: pads and volt meters
on Mar 9, 2008 at 8:58:36 pm

Craig,

Thanks for your patient reply. I've fed PD 150s before with no problem. I forget, perhaps it was at mic level. My Canon XL2 only takes line level though the unbalanced RCA jacks. So for it I always use the balanced mic level XLR inputs. I know that line level is a better defense against electrical/rf noises, but so far I have not had any problems.

So two thoughts. I think my calibration would work for the PD170 if you go mic level out of the mixer to mic level in on the camera. (wasn't there some other gotchas about noise with the PD 170? Seems I remember something but that was 3-4 years back. I think that may have been part of the reason I went with an XL2.)

When you tire of carrying around the extra pads, know that my Sound Devices 442 mixer has mic, -10 and line level output switches on two of its three stereo outputs.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Craig Alan
Re: pads and volt meters
on Mar 9, 2008 at 9:53:51 pm

Thanks.

Yeah, the vx2000 vx2100 pd150 pd170 all have noisy preamps. In my experience. it's best to feed them a strong enough signal so as to keep the cameras levels set as low as possible. I have gotten better results using line level in. However, getting the proper line level in here is the challenge. And yes I wish I had bought the sound devices mixer instead of the Shure mixer. That said, the Sony cams in this group and the Shure mixer were both industry prosumer level standards for years, so I'm surprised that I'm not getting readily available clear instructions on how to marry these two.

I think for the pads I'll get them with a short xlr cord. The shure mixer is in a porta-brace case and I should be able to run the short xlr out from the shure and Velcro it to the case. That part should be ok.

How do I use a voltmeter to measure the signals in and out of my mixer? Any suggestions on a model that won’t be over kill yet will take good measurements?

Also what do they mean by the voltmeter being parallel with the load?

VU Meter Adjustment
To set the VU Meters to a value other than the factory
setting (0 VU = +4 dBm), proceed as follows:
1. Connect a 600 load across the Left XLR output set
for Line.
2. Connect an ac voltmeter (such as the HP 400GL) in
parallel with the load.
3. Slide the 1 kHz tone oscillator switch to the On (up)
position.
4. Adjust the 1 kHz Tone Oscillator level with the Left
(inside) Master gain control until the ac voltmeter reading
is at the level desired.
5. Open the battery compartment door and adjust the
Left VU Level trim pot with a screwdriver until the Left
VU Meter reads 0.
6. Repeat the above procedure for the Right Output and
the Right VU Meter.
Limiter Threshold Adjustment
To adjust the Limiter threshold to a value other than the
factory setting (+15 dBm), proceed as follows:
1. Connect a 600 ohm load and an ac voltmeter across the
Left Line output as described in steps 1 and 2 of the
VU Meter Adjustment procedure.
2. Open the battery compartment and move DIP switch
1 to the Off position (refer to the chart on the inside of
the door).
3. Slide the 1 kHz tone oscillator switch to the On (up)
position.
4. Slide the Limiter switch to the Off (down) position.
5. Adjust the Left Master gain control until the ac voltmeter
reading is 2 dB above the desired output level.
6. Slide the Limiter switch to the On (LIM) position.
7. Open the battery compartment and adjust the Lim Adj
L trim pot until the level drops to the desired reading.
8. Repeat the above procedure for the Right output, using
the Lim Adj R trim pot.



OSX 10.4.11; Quicksilver Dual 1 gig; G5 dual 2.5 gig; FCP 4.5, 3.0.4; Sony camcorder vx2000/pd170;Canon xl2; Pana consumer cams; write professionally for a variety of media;teach video production in L.A.


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Ty Ford
Re: pads and volt meters
on Mar 9, 2008 at 10:02:43 pm

You can probably find a cheap VOM (volt-ohm-meter) at radio shack.
About the measuring. Not my best area, but I think you have to have the input and/or output terminated (connected) while measuring. That way the circuits are "under normal load."

I'm pretty sure "parallel to the load" would be measuring across pin 2 and pin 3.

Tell you what. Call Shure. They have a very good service shop. Let them help you with this.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Craig Alan
Re: pads and volt meters
on Mar 10, 2008 at 2:10:24 am

Thanks Ty. Yes what you say is my understanding. But I need the ignorant guide to doing this. Have no idea how to connect pins or how to connect the volt meter. etc. I'll call Shure. I have to admit I've had better luck on the phone with tech guys than email where their responses are often inc. or over my head. I learned a lot, for example, talking to a guy at mole richardson about their light kit.

Anyway thanks for helping. I'll keep your suggestions above about setting in mind once i sort out how to set the FP33 up. Shure still talks about it as a top end mixer and its still sold at BHphoto. But reviews of sound devices indicate its been replaced as the standard.

OSX 10.4.11; Quicksilver Dual 1 gig; G5 dual 2.5 gig; FCP 4.5, 3.0.4; Sony camcorder vx2000/pd170;Canon xl2; Pana consumer cams; write professionally for a variety of media;teach video production in L.A.


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