The USB microphone is a type of microphone that has become more and more popular over recent years. They're aimed more towards the podcasting market and are best suited to the spoken voice, such as in radio or voiceover work. But they can also be used for singing, or any sound source that is relatively loud and close to the mic.
However, I wouldn't recommend using a USB mic for serious recording when compared to the use of a normal XLR microphone. Some of the reasons why are explained below.
USB stands for Universal Serial Bus, which is an industry standard method of interconnecting different electronic devices. A modern PC or Mac usually contains between one and four USB ports, sometimes even more.
One of the positive aspects of the USB mic is the portability available to you. You only need one connection - the USB cable runs straight from the microphone into the computer. There's no need for an external sound card, mixer, or any kind of preamp. This can make it a great budget solution for location recording of spoken-word interviews.
But one of the drawbacks is the fact that when a signal is low in volume, the digital USB circuitry can introduce a lot of unwanted noise and distortion. They can also be difficult to set up correctly inside a computer when you want to record inside your DAW program.
Some USB mics have their frequency response tailored towards the spoken word, with a roll-off above 15-16 kHz and a presence peak around the 9-10 kHz mark to give the voice some "air" (a word used when higher frequencies of the voice are emphasized through the use of equalization).
The better USB mics usually feature a cardioid polar pattern, so they also display the proximity effect as well, where the lower bass frequencies get slightly louder the closer the sound source gets to the microphone.
The microphone itself contains a preamp along with an analog-to-digital converter (ADC), but alot of these devices don't feature separate gain controls which can be a problem if the source is on the quiet side. Latency can be very high with these mics, so to help combat this the microphone will sometimes have a headphone jack directly on it - this enables zero-latency monitoring directly from the microphone.
These microphones have both good points and bad points, a few of which we've looked at. If you're serious about getting quality recordings in your studio for your production work, then it would be much better to stick to normal XLR-based microphones.
But if you're liking the idea of a USB microphone, then a great lower-budget option would be the Blue Yeti USB microphone, the Audio-Technica ATR2500, or the Samson C01UCW. A great higher-end model to look at as well would be the Shure PG27.