USB sound card not detecting Shure mic

Question

I'm still not sure whether this is the right forum to ask this question. However, I must ask this somewhere.

I recently bought a cheap USB sound card [1], which seems to be using the chip CM108. It works well with my cheap desktop mic, service almost zero noise at 100%.

But the problem is, it fails to detect my Shure SV100 mic (which was the actual one that I bought this card for). The mic comes with an XLR to 1/4" cable, which I connected with a 1/4" to 1/8" converter pin in order to connect it with the sound card. This pin is functional while using with the built-in sound card (except that it produces a low output and a lot of noise).

In short, without the USB sound card, both mics work, but with noise. With the sound card, the cheap one works and Shure SV100 doesn't.

First I thought the problem would be of the pin which fails to convert the mic output to the correct channel. But when checked with Audacity in stereo recording mode, both mics produce (of course without the USB card) output in the same track. So that is not the problem. (Was it a foolish test?)

Now I think that the USB card ignores the mic due to its low output. Will that be the reason? What about impedance?

[1] https://www.snapdeal.com/product/quantum-usb-sound-card/1088942142

Answer 1

Computer microphone inputs, both the built-in kind and the external USB kind, are designed to be used with relatively high-output electret condenser microphones. But that dynamic mic (Shure SV100) is rather low-level output and will not work very well with "computer type" microphone inputs of any kind, internal or external. Your experiment vividly demonstrates this problem.

This is NOT an issue of impedance as the output impedance of most modern microphones, both passive dynamic and active condenser, are rather low (100s of ohms). Low impedance is desirable to keep the connection between the microphone and the mic preamp input rather impervious to picking up ambient interference.

The XLR output connector is rather a clue that the microphone is the old traditional kind which is not very compatible with the computer-type 3.5mm mic input.

You need some kind of "traditional" mic preamp with reasonably high gain and XLR input to get a good low-noise result from the Shure SV100. These are available in a variety of forms from small "XLR to USB dongles" (rather like your little USB gadget) to more flexible USB mic preamp/sound cards like Behringer U-PHORIA UM2 which is representative of the lowest-cost USB interface with a decent XLR mic input/preamp.