Dumb question from Supporting Member: Does -10db pad affect more than just amplitude?

[stridentlinear]

I've heard it said in passing that on a lot of mics, engaging the -10db pad sometimes affects more than just output level.

Any actual theory behind this, or is it just BS/urban legend?

Thanks in advance, from a supporting member.

 

[kingkorg]

I've heard it said in passing that on a lot of mics, engaging the -10db pad sometimes affects more than just output level.

Any actual theory behind this, or is it just BS/urban legend?

Thanks in advance, from a supporting member.

Depends on what kind of pad. If it's the kind of pad that where you reduce the polarization voltage of the capsule it shouldn't change the sound in any way. I'd say claims about this type changing the sound are urban legend.

Adding a cap somewhere in the hiZ area (there are different arrangements) will change the sound, but how much could be debated. Recent thread started by MicUlli points to possibility of even rising the THD by doing so. It will prevent the first stage from clipping tho.

There are some mics that have a pad in the end of the circuit, which just prevents preamp to clip. It doesn't really pad the first stage of the mic, so it might still clip, but might change the sound by altering the mic/pre interaction. Depending again on what kind of pad it is, where in the circuit, transformer or not.

 

[stridentlinear]

Depends on what kind of pad. If it's the kind of pad that where you reduce the polarization voltage of the capsule it shouldn't change the sound in any way. I'd say claims about this type changing the sound are urban legend.

Interesting, and thanks for the reply!

Will changing the polarization affect self-noise? Or is that also urban myth?

 

[kingkorg]

Yes it will, but if you think about it, you would use a pad with high spl, so the noise shouldn't be an issue.

Unless you are recording something with crazy high dynamic range. Which i had experience with, like some crazy concept theater shows with both whisper at distance, and special fx through PA like thunders, 30hz oscillators at high spl. In that case you would use a dual mic setup one being paded, the other one unpaded low noise.

 

[JohnRoberts]

I could imagine a difference if the pad changes the input termination impedance. Properly designed pads should present the same input termination impedance in or out.

JR

 

[abbey road d enfer]

Depends on what kind of pad. If it's the kind of pad that where you reduce the polarization voltage of the capsule it shouldn't change the sound in any way.

However, changing the polarization voltage changes the disphragm tension.
All the same, padding by putting a dead capacitance across the capsule or between drain and gate (turning the head amp into a "charge amp") changes the harmonic content of the signal.
In both cases, the difference is tiny, but real and measurable. How audible it is is debatable, though.

 

[user 37518]

I've heard it said in passing that on a lot of mics, engaging the -10db pad sometimes affects more than just output level.

Any actual theory behind this, or is it just BS/urban legend?

Thanks in advance, from a supporting member.

Yes, it is possible to affect something else, depending on how the padding is being implemented. In the general voltage divider case, it affects the loading of the mic, which could affect damping and frequency response. Some people, for example, claim that the API -20dB mic pre pads dull the sound. These arguments are not completely unfounded. A padding done by switching the windings on a transformer, also changes the input impedance of the pre.

 

[abbey road d enfer]

Some people, for example, claim that the API -20dB mic pre pads dull the sound.

To the extreme, ANY pad would dull the sound, if only because reducing level results in lesser excitation of the sensitive organs.

 

[soapfoot]

But those API 512 pads really seem to do something extra-obvious relative to other pads I’ve used

 

[Icantthinkofaname]

Depends on what kind of pad. If it's the kind of pad that where you reduce the polarization voltage of the capsule it shouldn't change the sound in any way. I'd say claims about this type changing the sound are urban legend.

Adding a cap somewhere in the hiZ area (there are different arrangements) will change the sound, but how much could be debated. Recent thread started by MicUlli points to possibility of even rising the THD by doing so. It will prevent the first stage from clipping tho.

There are some mics that have a pad in the end of the circuit, which just prevents preamp to clip. It doesn't really pad the first stage of the mic, so it might still clip, but might change the sound by altering the mic/pre interaction. Depending again on what kind of pad it is, where in the circuit, transformer or not.

I think a lot of people perceive a quieter signal as sounding "worse". Maybe it's that you're not perceiving the audio as having the same clarity, like listening to quieter music.

To the extreme, ANY pad would dull the sound, if only because reducing level results in lesser excitation of the sensitive organs.

This is a very good to the point way of saying what I'm trying to describe.

 

[kags]

I have a 32 channel API 1608 and can confirm that the pad affects the tone of a mic pre (only noticeable with dynamic mics in my experience). Not enough that I would avoid using the pad - probably made up for with 1dB or less of EQ in a mix. Maybe it even sounds better in some cases

 

[emrr]

But those API 512 pads really seem to do something extra-obvious relative to other pads I’ve used

So.....what are the values? Do you use inline pads instead with 'better' results? Is it an unavoidable loading condition related to those input transformers?

 

[soapfoot]

So.....what are the values? Do you use inline pads instead with 'better' results? Is it an unavoidable loading condition related to those input transformers?

Ashamed to say I never really investigated deeply, and now all of the ones I used to use are on the opposite coast.

But I want to say an in-line pad *did* work better once (ages ago), but most of the time I just use something else instead

 

[Екатерина]

More often, it only reduces the output level, and that capacitor will also reduce some harmonics, but you know this is insignificant for the overall sound

 

[kidb]

Yep, impedance and frequency response seems to change even if slightly. The interaction between a dynamic mic and an input transformer will change with a pad in the middle, given the impedance change of dynamic mics. I tend to think all pads sound bad, but how much of that is louder is always better, I'm not certain. The pads ive tended to prefer are L pads and H pads, most mic pres use a U pad which is standard, I use those too without thinking about it too much.

 

[abbey road d enfer]

Yep, impedance and frequency response seems to change even if slightly. The interaction between a dynamic mic and an input transformer will change with a pad in the middle, given the impedance change of dynamic mics.

That is correct, and quite well documented.
The art of a designer consists in optimizing the performance in consideration with the impedance changes due to different mic types or even as a function of frequency for a particular mic.

The pads ive tended to prefer are L pads and H pads, most mic pres use a U pad which is standard, I use those too without thinking about it too much.

There is no reason for an L-pad to sound better than a U-pad. One being only the balanced version of the other.
OTOH, H-pads are not well-suited for insertion between a mic and preamp. The main (only?) advantage of H-pads is that they maintain impedance matching on both sides, which is inadequate for mic/pramp combination.
The mic/preamp connection is bridging, not matching. The mic must see about 5-10x its nominal impedance. It's the reason that make a pad with less than 20dB attenuation unachievable.

 

[kidb]

That is correct, and quite well documented.
The art of a designer consists in optimizing the performance in consideration with the impedance changes due to different mic types or even as a function of frequency for a particular mic.

There is no reason for an L-pad to sound better than a U-pad. One being only the balanced version of the other.
OTOH, H-pads are not well-suited for insertion between a mic and preamp. The main (only?) advantage of H-pads is that they maintain impedance matching on both sides, which is inadequate for mic/pramp combination.
The mic/preamp connection is bridging, not matching. The mic must see about 5-10x its nominal impedance. It's the reason that make a pad with less than 20dB attenuation unachievable.

Totally agree. We’ll put ^
I’ve not used anything but a U pad on mic pres. I like an H pad on line level sources when necessary. Just my experience, haven’t done any exhaustive testing.
I tend to think the best pad is no pad,

 

[abbey road d enfer]

I have a 32 channel API 1608 and can confirm that the pad affects the tone of a mic pre (only noticeable with dynamic mics in my experience).

You can probably chalk it up to the fact that the mic faces two very different loads. With the pad ON, it sees essentially a resistive load of about 2 kohms, when with the pad OFF, it sees the xfmr primary, which is very inductive.
It seems part of the character of the API312 preamp is that the xfmr is somewhat undamped, which results in HF impedance rise, which gives dynamic and ribbon mics more "air".
OTOH, the pad can bring its own damping, so the effect will be very much source dependant.

 

[abbey road d enfer]

I tend to think the best pad is no pad,

Just a necessary evil.