I have a couple of devices with electret condenser mics, one is an old Casio PDA (running Windows CE), another is a 1/8" headphone adapter with a built-in microphone (for iPhone/iPad). Both devices have working mics, but recordings are noisy. The noise is slightly different in each case. With the PDA, recordings have a rumbling noise over them. With the iPhone adapter, recordings have a popping sound that appears every second or so. Does anyone recognize these symptoms and can they be fixed with a new electret mic element, or by some simple modification such as wiring a resistor or capacitor in? (I have a few electret mics taken out of old radios/etc, that may still be good.)

On Oct 24, 10:45*am, wrote:
I have a couple of devices with electret condenser mics, one is an old Casio PDA (running Windows CE), another is a 1/8" headphone adapter with a built-in microphone (for iPhone/iPad). *Both devices have working mics, but recordings are noisy. The noise is slightly different in each case. With the PDA, recordings have a rumbling noise over them. With the iPhone adapter, recordings have a popping sound that appears every second or so. Does anyone recognize these symptoms and can they be fixed with a new electret mic element, or by some simple modification such as wiring a resistor or capacitor in? (I have a few electret mics taken out of old radios/etc, that may still be good.)

My guess is that the noises are not the fault of the mic. That said,
you can always try another mic. Does either device offer the option
of recording an external input (not the built-in mic)? If so, try
that--I guess with the second device it IS an external mic. Some
noises are inherent in various lossy compression schemes, and some
devices (especially ones with a lot of digital stuff going on inside
them) don't do a very good job shielding sensitive analog inputs such
as a mic input from electrical noise generated in the device.