Topic: -10dB pads-- when do you use?

[DSatz]

Mr. Brecht (I admire your "Threepenny Opera" greatly, and also the "Life of Galileo"), being cheap is a prime reason to bring a pair of in-line resistive pads along to every recording you make. They are the lowest-cost problem-solvers and trouble-shooting tools for overload/distortion problems. If you have an otherwise good preamp or recorder whose mike inputs are prone to overload, in-line resistive pads can save you from having to buy an expensive, new preamp or recorder.

If you hear distortion in a recording and the meters didn't reach 0 dB, how do you know whether the microphone overloaded, or the input of the preamp or recorder overloaded? Simple: Put in-line pads at the inputs of the recorder. If the distortion goes away, it was the recorder inputs (and you now have the best possible solution in place). If it doesn't, then it was the microphone; throw the -10 dB switch and remove the in-line pads. But also PUT EARPLUGS IN because any sound that can overload a modern condenser microphone is very dangerous to your hearing.

This assumes that the microphones are being correctly powered. Condenser microphones that aren't properly powered will generally have problems with premature overload. It also assumes that wind or other strong air currents aren't a factor; they can overload directional microphones without necessarily being audible in and of themselves, especially if your microphones have output transformers. And an underpowered microphone where there is also wind is a disaster waiting to happen.

--As to your main question, an increase in noise relative to signal is the main ill effect of using a built-in, capacitive pad, but there is often a considerable increase in distortion as well. A report about this was published in the Journal of the AES in 2002 by Drs. Pastillé and Ochmann from Berlin, entitled "The 10 dB switch in condenser microphones." The upshot is that it depends on how the pad is implemented and some other factors such as stray capacitance. The traditional approach, which is to add a fixed capacitance in parallel with that of the capsule, can cause a marked increase in distortion (like tripling or quadrupling it).

Some more recent microphones implement the pad by reducing the polarization voltage to the capsule. This doesn't help the noise any, but it doesn't make the distortion worse, either, so it's a better approach. So far, though, I've seen it used only in certain Neumann microphones--it does complicate the DC converter arrangement a bit.

--best regards

P.S.: On a threaded discussion board such as this, everyone can see all the messages that led up to any given posting. I appreciate your enthusiasm for what I wrote, but it strikes me as a waste of bandwidth to quote an entire message back. Of course if there is a particular phrase or sentence that you want to single out for reply (like if it changed your life) then by all means ...

[taperj]

Yo! People!

The ONLY time to use the pad switch on a microphone is when the microphone ITSELF would be in danger of overload if you didn't. It's nearly impossible to overload the capsule of a condenser microphone with loud sound, but the electronics of a microphone can be overloaded by the signals from its capsule. The pad exists SOLELY to prevent that type of overload, and shouldn't be used for any other reason because it raises the noise floor of the microphone by the same amount (10 dB in this case).

If your microphone is NOT being overloaded but its signals are overloading the input of your preamp, mixer or recorder, then the thing to use is a resistive pad at the input of said preamp, mixer or recorder. Such pads will not raise the noise level of the microphone as using its built-in pad will do.

Get it? (Please?)

Excellent, then my logic was correct that my inlines will not degrade SNR like an on-mic attenuator. Thanks DSatz

[datbrad]

One thing I was told by both Doug Oade and Jim Williams years ago was that the -10 switch on AKG 460s is not a resistive pad, but instead a sensitivity switch. I assume this is why there is no change in the specs from the manufacturer for noise levels and THD on the data sheets that shipped with the 460s, compared to the 480s where there is a defined change in SNR specs when moving the switch on the 480s.

I did some home testing on my 460s back in '98, when the 480s were a new model and I first saw the noise spec changes related to the "pad" switch in that mic's manual, to determine if this was also a factor with the 460s, just not published in the specs.

What I found was no audible change in noise when the recorder levels were matched after moving the -10 switch back and forth. This was simply recording in the living room capturing mostly ambient sounds, allowing any hiss to be clearly audible.

Don't know if any other 460 owners have found this, but since that time I have used the -10db position always on them for over a decade now and not had any audible noise issues. I like the comfort of the increased headroom I always have with the -10db engaged on the 460s, and probably will never go back to "0" on the mic switch. Just my own personal experience, YMMV.........

[newplanet7]

What I found was no audible change in noise when the recorder levels were matched after moving the -10 switch back and forth.

Don't know if any other 460 owners have found this,

Here.

[acidjack]

What I found was no audible change in noise when the recorder levels were matched after moving the -10 switch back and forth.

Don't know if any other 460 owners have found this,

Here.

Anyone know if this is true of the Beyers?  The show I am doing tonight is going to be pretty loud ("punk" band, small venue with very good sound system)... The R-44 has a clip light, but as I've been fortunate enough not to have it kick on, I don't know whether that's sufficient.

To be clear, though, I don't think this show will be nearly loud enough to overload the mics themselves... so should the clip light then be sufficient?

[page]

What I found was no audible change in noise when the recorder levels were matched after moving the -10 switch back and forth.

Don't know if any other 460 owners have found this,

Here.

Anyone know if this is true of the Beyers?  The show I am doing tonight is going to be pretty loud ("punk" band, small venue with very good sound system)... The R-44 has a clip light, but as I've been fortunate enough not to have it kick on, I don't know whether that's sufficient.

To be clear, though, I don't think this show will be nearly loud enough to overload the mics themselves... so should the clip light then be sufficient?

What's your max mic-in value on the r-44 (assuming beyers > r44 without a preamp between them)?

If you don't think it will be enough to overload the mics (and I doubt it would be personally), then the next concern becomes the pre-amps in the box which should have a db rating.

[acidjack]

Correct, running direct into my R-44.  The deck has input sensitivity settings, which I only find myself having to lower generally for SBDs. Sensitivity can go all the way down to -56dB.  The manual says that "when the sensitivity setting is too large and clipping occurs" the lights on the affected channel light up. I have seen this happen when running an SBD feed, and reduced those sensitivity knobs accordingly.

Max Input = +24dB

It sounds like changing the input sensitivity knobs is all I'd need to do, I think.... ?

[page]

Correct, running direct into my R-44.  The deck has input sensitivity settings, which I only find myself having to lower generally for SBDs. Sensitivity can go all the way down to -56dB.  The manual says that "when the sensitivity setting is too large and clipping occurs" the lights on the affected channel light up. I have seen this happen when running an SBD feed, and reduced those sensitivity knobs accordingly.

Max Input = +24dB

It sounds like changing the input sensitivity knobs is all I'd need to do, I think.... ?

I forgot that the R44 didn't publish two specs cause it uses an adjustable sensitivity setting. It should be ok and you adjust the sensitivity knobs some. I remember doing that for my fostex on occasion when I changed mics, I had to change stuff. On the fostex, there was a formula for how far to turn so you could do it before getting into the field. I don't know if there are published specs (I guess -56 and +4 at the other end) but you should be able to figure out how hot to run it before you get out there.

[acidjack]

^^ Thanks.  I was especially fretting about it as I forgot to bring my monitoring headphones with me today and won't be able to check on it between bands... Plus I suppose I have been lucky to have idiot-proof gear in the past with few real "options" that I could screw up!

[dean]

Thanks for the info, Mr. Satz!

Brad, any idea if what's true for the 460's is same for 414's?

[taperj]

A report about this was published in the Journal of the AES in 2002 by Drs. Pastillé and Ochmann from Berlin, entitled "The 10 dB switch in condenser microphones."

Thanks to a taperjoe and a friend of his who is a member of the AES I was able to get a copy of this study and read it cover to cover last night. A good read, lots of math.

I think of the whole study the excerpt that strikes me as explaining exactly what we are trying to get at in this thread is here...

"   If an audio engineer desires distortion-free recordings,
a careful consideration of the microphone circuit dia-
gram is necessary. A good option is to use a microphone
with a high level limit. The development of a micro-
phone amplifier with a maximum input voltage of 5.5 V
by a German manufacturer1 makes the discussion of the
10-dB switch obsolete. In this case a reduction of the
output signal is possible using a passive network.
However, it should be noted that the distortion can be uti-
lized for artistic purposes."

This plainly states that for distortion free recordings, DON'T use your mic pad, use the pad in the amplifier(or something inline), that's what they were made for. If the mic capsule is distorting, use the on-mic pad. Notice the main concern here isn't even noise floor(SNR). It's distortion, which IS a concern, much moreso than SNR according to the study. Thanks to DSatz for pointing me to the study, it was a good read, learned a ton.

Ok and, these guys look like they not only know what they're talking about, they look like some serious party animals, someone invite them to the next show!

[datbrad]

Thanks for the info, Mr. Satz!

Brad, any idea if what's true for the 460's is same for 414's?

You know Dean, I am just not sure even about the truth on the 460s. I am making an assumption that because the spec sheet in the manual for the 480 shows a change in noise specs when the pad switch is moved, and the 460 manual shows no change between 0 and -10, that it's meaningful and not a simple omission by AKG on the 460 manual to show everything. Add to this my purely subjective listening tests, and I think I am correct about the 460s.

I think the old 414 ULS is the same as the 460B ULS, but I am not sure about the 414 XLS. It could be a similar relationship. Am I correct that the 414 ULS has a transformer, and the 414 XLS is transformerless? The transformers could be a factor here, I just don't really know. Guess I did not really answer the question, but I hope this helps add to the discussion.

[dean]

Thanks for the info, Mr. Satz!

Brad, any idea if what's true for the 460's is same for 414's?

You know Dean, I am just not sure even about the truth on the 460s. I am making an assumption that because the spec sheet in the manual for the 480 shows a change in noise specs when the pad switch is moved, and the 460 manual shows no change between 0 and -10, that it's meaningful and not a simple omission by AKG on the 460 manual to show everything. Add to this my purely subjective listening tests, and I think I am correct about the 460s.

I think the old 414 ULS is the same as the 460B ULS, but I am not sure about the 414 XLS. It could be a similar relationship. Am I correct that the 414 ULS has a transformer, and the 414 XLS is transformerless? The transformers could be a factor here, I just don't really know. Guess I did not really answer the question, but I hope this helps add to the discussion.

That helps.  Means I can't make any assumptions very safely.  Thanks!

[acidjack]

FWIW, in case anyone needs the info in the future, I ran the MC950s last night without the pads but did lower the input sensitivity on the R-44 by a couple clicks down from -0.  No distortion whatsoever.  This neither proves nor disproves whether to use the pads in certain situations, but I think the answer would be, "It depends on your equipment."

For the R-44 and other decks where you can adjust input sensitivity, I think the answer seems to be pretty clearly "no."

[taperj]

^^ Thanks acidjack, I was going to ask how it all worked out if you didn't post. Great to hear you came out clean