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Old June 12th, 2006, 11:56 PM   #1
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Microphones & Pads

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If the microphone output voltage exceeds the input capability of the microphone preamp, the sound will be distorted no matter where the level control is set. Pads are necessary to keep the maximum output of the mic from exceeding the input capability of the preamp.

Source: Holman, T 2005, Sound for Digital Video, p.128, ISBN: 0-240-80720-0, Focal Press, USA
I never even thought about that! After reading about pads before preamps, I suddenly had a big "oh yeah!" moment. Makes so much sense!

Unfortunetly the math behind it went way over my head. It's going to take a couple of days of re-reading to get my head around the numbers.

Now, in practise, I've never had any problems with mics hooked up to my Z1P (distortion wise). Having said that, I only really ever record dialog and other random stuff (doors closing, atmos, cars starting, etc.) - nothing overly loud.

I'm just wondering if anyone actually uses pads in a "prosumer" environment?

For example, when connecting a ME66 to a PD170, the author suggests a -22dB pad to match the microphones maximum output to the electronics microphone input maximum undistorted level. Do anyone actually do this in practise?

Just wondering!

~ Chris!
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Old June 13th, 2006, 08:35 AM   #2
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Yes, we do. If you search on "ME66" here, you'd find a number of posts about that particularly hot mic causing distortion, and the resulting advice being to pad (aka attenuate) it.

Last week I recorded a concert with a pair of AT3031 mics arranged for stereo. I found that I needed to attenuate them by -10dB due to the loudness of the program material.
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Old June 13th, 2006, 08:48 AM   #3
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Quote:
Originally Posted by Chris Hocking
I'm just wondering if anyone actually uses pads in a "prosumer" environment?

For example, when connecting a ME66 to a PD170, the author suggests a -22dB pad to match the microphones maximum output to the electronics microphone input maximum undistorted level. Do anyone actually do this in practise?

Just wondering!

~ Chris!
Yes: me too! See here. Even using the MIC ATT setting on the PD-170 doesn't fix this, being AFTER some active (and hence clippable) part of the mic preamp circuit. Sony madness, that. Hence the need for an EXTERNAL pad.

BTW: The -20dB pad with resistor values as shown can be made up via DIY, and works well.
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Old June 13th, 2006, 09:46 AM   #4
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Martin - have you used those Canford attentuators?

If so can you comment upon them ? good items to get?

http://www.canford.co.uk/commerce/pr...oductid=20-910

thanks
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Old June 13th, 2006, 10:36 AM   #5
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Quote:
Originally Posted by Stu Holmes
Martin - have you used those Canford attentuators?

If so can you comment upon them ? good items to get?

http://www.canford.co.uk/commerce/pr...oductid=20-910

thanks
No, I built my own in a male/female pair of XLRs and a short lead. But I believe the Canford inline pads are fine - a bit pricey for what they are, and a bit less convenient to handle on camera - i.e. bulky and quite long compared to the short XLR-XLR lead you need on camera anyway. Hence my reason for building my own.
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Old June 13th, 2006, 05:21 PM   #6
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Thanks for your comments everyone!

Can you use multiple pads inline? For example, can you use two 10db pads if you require a 20db pad?

Also, you can't use phantom with a pad inline (well, so I've read). What devices are people using if their mics do not have internal batteries? Even if they do have internal batteries, do you achieve better results with a "after pad" phantom powering device?

Thanks! ~ Chris!
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Old June 13th, 2006, 08:26 PM   #7
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The pad should be used ideally pre the amplification stage (aka preamp). There's no much sense if you use a pad post the preamp stage because the preamp stage might be already clipped. I don't know if I'm explaining myself correctly, but in that case you'll only lower the clip, but the audio will already be distorted.
Another solution could be to use a variable passive pad. In the studio, I use one made by A-Designs Audio.
http://www.adesignsaudio.com/atty.htm
Great thing about this small box is that it is an entirely passive, variable level control. I've used it prior to preamps to control levels and avoid clip at the preamp input stage, sometimes at the output of the preamp to control level prior to the A/D stage.
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Old June 13th, 2006, 09:25 PM   #8
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Chris, yes you can add pads in line.

Also, some pads (attentuators) are designed for use with phantom power. Here's one I recommend. Besides being compatible with phantom power, it has a slide switch for selecting -10, -20 or -30 dB. I have two of them and they're great.

http://www.bhphotovideo.com/bnh/cont...ughType=search
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Old June 13th, 2006, 11:09 PM   #9
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Quote:
Originally Posted by Fred Retread
Last week I recorded a concert with a pair of AT3031 mics arranged for stereo. I found that I needed to attenuate them by -10dB due to the loudness of the program material.

I've used AT3032s around bands and have to
attenuate them 30dB going into a Sony PD.
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Old June 13th, 2006, 11:12 PM   #10
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Quote:
Originally Posted by Martin Mayer
Yes: me too! See here. Even using the MIC ATT setting on the PD-170 doesn't fix this, being AFTER some active (and hence clippable) part of the mic preamp circuit. Sony madness, that. Hence the need for an EXTERNAL pad.
I've always had luck using the MIC ATT setting
as a pad. From the way it has worked for me
it seems that the pad is BEFORE the active
part of the preamp circuit.
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Old June 14th, 2006, 08:13 AM   #11
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Thanks for your replies everyone...

Berns: Yes, you explained yourself well and yes, I do understand where the pad must go in the signal chain to be effective. Thanks for pointing out the variable pad - I didn't even think about that!

Fred: I understand that you can add pads in line. My question was, can you use two pads to double the effect? For example, instead of using a 20db pad, use two 10db pads? Will it affect the quality of the signal. I didn't know that you could get pads that allowed phantom to pass; thanks for pointing that out!

Dave: What kind of camera are you using? Does your camera documentation state where the MIC ATT pad is in the signal chain?
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Old June 14th, 2006, 08:20 AM   #12
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Quote:
Originally Posted by Chris Hocking
Dave: What kind of camera are you using? Does your camera documentation state where the MIC ATT pad is in the signal chain?
Sony PD. No, the documentation does not say
where the pad is but by engaging the MIC
ATT this takes away the distortion. I do this
all the time as I record live bands. There really
has been no doubt in my mind that the
MIC ATT pad is BEFORE the preamp gain
circuit.
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Old June 14th, 2006, 08:31 AM   #13
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Cool... Thanks Dave!
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Old June 14th, 2006, 09:33 PM   #14
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I have always used the Shure in-line attenuators, for -10, -15, and -20. I have one attatched to my 66' and 4 or 5 spares just in case. IMHO, the best - easy to fix.
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Old June 14th, 2006, 10:13 PM   #15
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Quote:
Originally Posted by Chris Hocking
Fred: I understand that you can add pads in line. My question was, can you use two pads to double the effect? For example, instead of using a 20db pad, use two 10db pads? ...
Yes, two tens will add up to a twenty. What did you think I meant by adding them in line? 8>)
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