Attenuator for mic input

Slightly basic for this group, but also slightly audiophool, so I figured I'd ask here anyway.

I've got an electret lapel mic that I'm using with my smart phone for making videos. It's pretty good, but it's hot enough that the audio bars on the phone are showing red on audio peaks. I'd like to try toning it down in electric-land so that things aren't clipped going into the phone.

So -- is there a way to attenuate the audio coming out of an electret in a way that doesn't appreciably cut power to the microphone, while retaining the audio quality (which I like)?

I suppose I could make a little battery-powered box that completely isolates innies and outies, but at this point I'd be MUCH happier if the job could be done satisfactorily with some network of resistors and caps, with one variable element to change the volume -- or even a fixed network, since I just want to get things into the phone's happy range and plan on adjusting things more in the video editor.

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Tim Wescott
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electret mics need power

does your mic get power from the phone

I think you can pretty well consider the mic FET output as a current source and if you simply lower the load resistance, it will lower the audio.

But you want to keep the DC bias point about the same so you might need to use 2 resistor, one to the supply and one to ground to keep the DC point the same but to lower the AC load....

Or you could AC couple in a load resistor with a BIG cap.

mark

Reply to
makolber

Den mandag den 10. oktober 2016 kl. 22.15.18 UTC+2 skrev Tim Wescott:

I'd try a resistor in parallel, It'll steal some of the bias and load it some

-Lasse

Reply to
Lasse Langwadt Christensen

If your audio input accepts stereo, you could try feeding left channel with unattenuated output, and right channel through a divider. Then at the video composition step, you can select the sound track that works best, switching for best effect. Background hiss will show up at an abrupt switch, so some filtering and ramping functionality would be good.

A few peaks into the 'red' aren't a bad thing, necessarily. Your ears do the overload thing anyway, and Haydn's "Surprise" wouldn't be the same without levels in the red.

Reply to
whit3rd

Wrap the microphone in cloth ;-)

Some 50 years ago, at Motorola SPD, we had an engineer with a booming voice... knock your ears loose when you'd answer a call from him.

So I cut out a circle from a black piece of paper, unscrewed his telephone mouthpiece, inserted paper, replaced mouthpiece... problem solved... he never noticed in the 8 years I worked with him ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

This may be the winnah -- at least, I'll probably try it first.

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Reply to
Tim Wescott

A parallel resistor should cut amplitude, stick a capacitor in series with the resistor to block DC. maybe try 330R and 33uF.

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Reply to
Jasen Betts

How about shunting with a cap (say 10uF) in series with variable resistor (say 1k) so the cap leaves DC bias untouched but lets the AF be shunted by the R?

piglet

Reply to
piglet

Long ago at IBM, some bright boy in Safety decided that since some labs wer e noisy (having things like 200 rack mount server boxes or a big cryopumped vacuum system), _all_ labs were to be fitted with big horn PA speakers so that everybody would hear evacuation announcements and so on. Of course no volume control was provided.

It was a great idea except that every time they came on the PA to announce a talk, or some management droid holding a meeting, or a blood drive or som ething, you jumped right out of your skin and broke whatever delicate devic e you were working on.

Disconnecting the speaker was stated to be a firing offense. Soooo, I and (independently) probably everybody in the building went down to the stockro om for a small rubber stopper, disassembled the horn, and crammed the stopp er down in the bottom of the inner horn.

Problem solved--the safety idiot got his award and we got to keep our eardr ums.

Cheers

Phil "doesn't miss Corporate America much" Hobbs

Reply to
Phil Hobbs

I kind of arrived at that given a previous post -- how much chance is there that it'll leave the frequency response unmolested?

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Reply to
Tim Wescott

Bo Widler, when at National, used a plumber's helper loaded with a cherry bomb... hold against ceiling speaker >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

The stopper method worked great--I could still hear the PA, but it was nice and quiet. Widlar was consciously trying to create a legend--see e.g. the careful photo documentation of his sheep on National's lawn--but I just wanted to get on with building stuff. Plus nobody could say that I damaged company property. ;)

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

AFAICS it's *bound* to have *some* effect. It would take all of 2 mins to Spice it; try it.

Reply to
Cursitor Doom

looks flat like a table trough the voice band (300hz to 3000hz): the corner frequency is below 20Hz. how good's your electret down there.

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Reply to
Jasen Betts

Capacitive potential divider, assuming your amp Zin is high?

Cheers

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Syd
Reply to
Syd Rumpo

A resistor divider on a capacitive source will lose lf.

NT

Reply to
tabbypurr

There is a buffer amplifier (most often FET source follower) after the capacitive element in the mic, so the source is not capacitive anymore.

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-TV
Reply to
Tauno Voipio

Without knowing the characteristics of the phone or the mic I have nothing to Spice.

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Reply to
Tim Wescott

But does the mic look like a purely resistive source?

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Reply to
Tim Wescott

Just add a coupling cap (if it doesn't already exist), and load it down resistively, the cap and load R will determine the low end. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson

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