Things to look for when buying a usb microphone:-

2. Signal-to-noise ratio

Signal-to-noise ratio (SNR or S/N for short) is an indicator of the quality of sound reproduced from a USB microphone (or other instrument). A high ratio will mean a faithful reproduction of music, a low ratio will mean that there is a good deal of background noise present in the signal from the microphone.

3. Build quality

Is it durable? Does it have a stand? Is the stand reliable or does the mic "flop" down too easily?

4. Length of cable

This is surprisingly important. If you intend to use the mic to record instruments you will need a cable of at least 2 and probably 3 meters long.

5. Stereo or mono?

Most usb mics are in mono. There is an obvious advantage in mono recordings - they produce smaller file sizes compared to a stereo equivalent (the average file size of a stereo 44.1 wave file is roughly 10meg for every minute recorded). However, recording in stereo may be important for you if you intend to capture something "live" (eg a concert or recital), as recording in stereo helps to preserve the sense of space between instruments or sound sources.

6. Omnidirectional or unidirectional microphones

An Omnidirectional microphone will pick up sound from a very wide field. The unidirectional mic records sounds in just one direction. Unidirectional mics are often used for amplifying live vocals, where the focused field is helpful as picking up noises from a wide source can lead to "feedback" issues. Omnidirectional mics are often used where a mic needs to pick up a very wide spread of sound (e.g. a live choir or to record the audience reactions). Some USB mics (such as the Yeti by Blue Microphones) have a bio directional option - meaning that the microphone can pick up from in front and behind, but not at the sides.

What is a USB microphone, and how does it differ from a conventional one?

USB mics house the same technology as traditional mics (e.g. a diaphragm, a capsule), with the exception of two important features:-

1. A USB mic contains a pre-amp. (A pre-amp is a small amplifier that increases the output of the signal). Hence there is no need for a separate pre-amp between the mic and the computer.

2. A USB mic has an in-built analog-to-digital converter (known as an A/D converter for short). A/D converters take an analog voltage signal and encode it as a digital number. This information can then be read by a computer via a USB input.