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I have a condenser microphone which is powered over USB (MPM-1000u if you care - it has a cardiod pattern).

It was working fine, but recently it seemed to stop working - it didn't seem to record anything. However, I discovered that if I have it directly up against my lips and speak, it seems to record just fine.

Perhaps it's been too long since I did E&M, but I can't think of any reason that this would have happened. I can imagine sound not being recorded well, or at all, but this eludes me.

Can anyone explain to me what could have happened?

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  • \$\begingroup\$ Just spitballing. But usually there is some kind of automatic gain control (AGC) in the microphone gain chain. Maybe the AGC has stopped working for some reason (hardware or firmware change or damage?). The actual variation in sound pressure level to the microphone is huge because some people hold it inches from their mouth and others expect it to work across the room. Maybe the gain is now fixed at a relatively low level. \$\endgroup\$
    – user57037
    Commented Dec 21, 2020 at 6:21
  • \$\begingroup\$ Tip: "... only record very close sounds" is very unlikely. Sound pressure falls off at a rate given by the square of the distance. You mean that its sensitivity appears to have decreased. (It will still detect far away sounds if the level is high enough.) \$\endgroup\$
    – Transistor
    Commented Dec 21, 2020 at 18:42

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Welcome to the board, Joel. Let's try to do some remote troubleshooting.

It's important to recognize that the problem could originate not just in the microphone, but in the computer's USB sound driver and its settings.

Before blaming the microphone, review your computer's sound settings, in particular the microphone volume/gain setting. I can't give you exact instructions because they vary with operating system and sound drivers, but look for a microphone or input gain setting, as well as any "automatic" option (disable that). There's usually a built-in test function to see whether the signal coming in is of a normal level when you talk.

Also look at whatever application you're using to record the sound. Could a gain setting in that software have been changed inadvertently?

If you have access to another computer, it's worth swapping it in. If the sound remains low, then it probably is the microphone itself. (I'm not going to insult you by suggesting you make sure you're talking into the front side of the microphone.) The condenser capsule could have been damaged if the microphone was dropped. Or the circuit could have failed from a static discharge when the USB plug was inserted. None of these are easily fixable unfortunately. Is it under warranty?

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The MPM-1000U is the USB version of the MPM-1000, which operates from 48V phantom power.

Maybe there is an internal boost converter which has failed, and the capsule is only getting 5V.

Just a guess.

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  • \$\begingroup\$ Don't guess, read the datasheet. The MPM-1000u has an electret mic where the 48V is stored in the electret material. it produces a digital USB output. \$\endgroup\$
    – Audioguru
    Commented Dec 22, 2020 at 0:23

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