Wanting a microphone that picked up less noise and was more sensitive to soft sounds than the mic built into my laptop, I picked up the cheapest condenser mic I could find on Amazon, the Nady SPC-15 — in fact, I bought two as there was a special. It is connected to a M-Audio Fast Track Pro USB audio interface.
However, there is a constant noise distinctly audible when the gain is turned high, on one of the microphones. This noise varies in pitch or disappears entirely depending on:
- the physical layout of the USB cable and hub (noise still present without the hub) connecting the audio interface to the computer and power source,
- the setting of the gain knob on the audio interface and whether one or two microphones are connected, and
- physical disturbance of the microphone.
I would guess based on this evidence that the microphone is picking up the noise from its phantom power.
Here is a recording of the noise, and its absence with the other microphone. In this recording, I swapped only the mic, using the same cable and input jack. (The other input jack gives the same results.)
I want to know whether this noise's presence in one microphone
- indicates a defective unit?
- is normal manufacturing variation in cheap condenser mics?
- is a consequence of abuse, and if so what kind? (Mechanical? Hot-plugging? Leaving the mic powered for long periods?) I am especially concerned about this because the microphone without the noise is the one I have not used as much.