Topic: Use 10db Pad on Blue Lines with DR-70D?

[RABinMS]

I just got a Tascam DR-70D and am expecting to be able to try it out in a couple of weeks in a festival type setting. In the past I've taped occasionally with my AKG blue lines (powered by battery boxes) into SBM-1 into a D8. The very first time I tried that setup several years back it brickwalled, even though the level looked OK on the D8. I then engaged the 10db pad on the mics and that arrangement has worked fine ever since.

Does anyone have an opinion (hopefully an informed one) on whether I should leave the 10db pad engaged when using with the DR-70D? I'm planning to use the 48v phantom power and start out with the input gain on low. Will the combination of the pad and gain setting be too much? Should I use one or the other, or if leaving the pad engaged should I up the gain?

Thanks in advance for any advice. Mods if this isn't in the correct place please move.

[Life In Rewind]

I say no pad. But have no direct experience with that mic.

I havent had level issues running in front of loud-ish PAs.

If you find yourself with the levels almost all the way down - and your're still getting a lot of red light peaks - then you might need them.

[DSatz]

The pad switch on a condenser microphone is designed to prevent the microphone from being overloaded by very high sound pressure levels. It does this by making the input to the microphone's circuitry less sensitive.

When you use the pad switch, the signal level going in to the circuitry from the capsule is reduced by 10 dB (or whatever), but the inherent noise level of the circuitry remains unchanged. So the pad switch makes the microphone 10 dB (or whatever) noisier relative to the signal, and 10 dB more vulnerable to interference as well. Furthermore, the pad switches in many microphones indirectly cause increased distortion.

In short, the pad switch is for emergencies only, and should not be used unless the microphone is in real danger of overload due to extremely high (generally for modern microphones, humanly intolerable) SPLs.

It sounds as if your microphones aren't in any danger of overload, but their output levels are too "hot" for the inputs of your preamp or recorder. If so, you need resistive pads at the inputs of your preamp or recorder (on the far end of the cables away from the microphones). They preserve the signal-to-noise ratio of your setup, since they reduce the inherent noise of the microphones by the same amount as the useful signals. Meanwhile, signals in the cables (up to the inputs of the pads) remain at the higher level, so any interference that's present will have that much less effect on the recording. A 10 dB (or greater) reduction in interference makes a very welcome difference!

You can get high-quality, relatively inexpensive balanced resistive pads (built into XLR barrels) from many sources. I recommend the ones made by Shure; I've measured quite a few of them and I know that their balance is very good; that's important in keeping interference to a minimum. Other brands may be equally good but I haven't measured them, so I don't know for certain. -- These pads are purely resistive, and phantom power passes through them with generally negligable effect.

Of course, some recorders have switchable input attenuation built in, or a "low/high sensitivity" switch of some kind. If that's available, it's usually a good alternative.

--best regards

[RABinMS]

Thanks for the input. DSatz, you may well be correct about about the mics overloading the input instead of being overloaded themselves, but I don't have a way to measure that. The issue that I mentioned from several years back was at high SPL in a small club. While you're right that introducing pads in between the mics and pre or recorder inputs would lower the levels appropriately I'm really looking for opinions (if anyone has any experience with this yet) on whether any such padding should be necessary. Big change in my setup. Old - mics-> 18v battery boxes-> SBM-1-> D8, New - mics-> DR-70D with 48v.

Thanks in advance for any additional input on whether any padding is likely to be needed in a festival type setting (i.e. outdoors vs. small indoor club).

[Life In Rewind]

On your old rig - were you using the -20db pad on the SBM-1?

[RABinMS]

Had forgotten about that, but just checked and no, no pad set on the SBM-1.

[aaronji]

Those mics have a sensitivity of 10 mV/Pa and max SPL of 132 dB (per AKG).  At max SPL, they'll be putting out 0 dBu.  Tascam says the max input level for the DR70D is 0 dBu/20 dBu (mic/line).  So you should be OK without a pad (assuming everything is to spec), although mic in at SPL approaching 132 dB might be pushing it a bit...

[Jamos]

Agreed with DSatz on the placement of the attenuator. 
I just did a project where we needed attenuation in conjunction with a Sound Devices MixPre.  We went with these Audio Technica adjustable pads, and have been totally happy with the results:
http://www.bhphotovideo.com/c/product/68085-REG/Audio_Technica_AT8202_AT8202_In_Line_Attenuator.html

The Shure ones are great, as well as ones made by Whirlwind.

[Life In Rewind]

Had forgotten about that, but just checked and no, no pad set on the SBM-1.

For PA/AUD recording - you should have had the -20db on the SBM1 - thats a standard best practice with any Sony decks/pre of that era. (and a better spot to use an attenuator per DSatz comment)

[RABinMS]

Thanks again to all for the comments. Jamos, I'll keep those AT pads in mind. Looks pretty handy to have selectable values should the need arise.