How you sound in your podcasts is immensely important - second only to your actual content. Your podcast microphone is the first element in a chain of things which affect how you sound to your listeners; a good choice will provide clean, authentic audio for your signal chain and happy listeners eager to hear you speak.
TL;DR: Consider a high quality USB microphone for making your podcasts. Do your voice processing digitally in your computer.
SIMPLIFIED PODCAST AUDIO SIGNAL PATHS [USB Mic]--Digital Audio-->[SOFTWARE PROCESSING]-->[STORAGE and INTERNET] <------Digital audio requires a powerful PC (plentiful these days)--> [XLR Mic]--Analog Audio-->[HARDWARE PROCESSING]-->[ADC]-->[STORAGE and INTERNET] <-------Analog audio picks up noise---------->
The podcast microphone should be sensitive, yet contribute very little self-noise to the audio signal. The podcast microphone also needs to handle loud sounds, not overloading when there are loud voices or musical instruments. Unlike microphones used by field recordists and birdwatchers, a podcast microphone needs to have a directional pattern (to reject surrounding noise) as well as a flat frequency response across the human voice range. See the list below for specific electrical parameters for the best podcast microphones.
SEEK THESE MICROPHONE AUDIO PARAMETERS Transducer Type: Dynamic or Electret Condenser Directivity: Cardioid (insensitive to off-axis noise) Frequency Response: 20 to 20000 Hz Sensitivity: -30 dBV (referenced to 1V / Pa at 1 kHz) Max Sound Pressure: 110 dB SPL Self Noise: 16 dBA or less Total Harmonic Distortion: less than 0.05% Dynamic Range: more than 90 dB
Why select a USB microphone when there are so many excellent studio microphones with XLR connectors? In truth, you could use an XLR microphone, perhaps plugged into a preamplifier and processor. At some point, you must digitize the audio for editing and upload to your podcast platform. If you insist on using an XLR microphone, feed it directly to a quality analog to digital converter (ADC). Thence, feed the digital data stream to the studio or office PC for processing.
Whether you use a USB or conventional microphone for your podcast, it is essential to convert your audio to digital as early as possible in the signal chain. The farther down the chain an analog signal moves, the greater the probability of picking up hum and distortion. Power mains, mobile phones, nearby radio transmitters, and poor grounding all add up to noise, which you do not want on your voice signal. When you digitize right away, you eliminate those sources of noise. A regular desktop computer can run all of the necessary editing and signal processing software to give you a great sound. In fact, software processing is at least on par with (and often superior to) the best external processor devices. Digitize at the podcast microphone and use software for everything you need to do with your signal.
As to the digital parameters of the microphone, choose a podcast microphone which produces a high resolution audio stream. One which produces a 24 bit, 96000 sample per second stream via USB is all you need to record HD audio in a home or office studio. As a bare minimum, you could work with 16 bit / 48 ksps audio, then upgrade when you can obtain better equipment. I advocate the higher sampling rates and bit depths because they are better for processing,editing, and archiving. For recording out in the field, there are several very nice field recorders available. Some of them function as miniature portable studios with storage and a few digital processing functions.
USB MICROPHONE / DIGITAL RECORDER PARAMETERS Bit Depth: minimum 16 bits; 24 bits far better; 32 bit float is overkill Sampling Rate: 48000 (minimum); 96000 (standard); 192000 (superb) Note: 32 bit float format is ideal for signal proceesing, but excessive for recording spoken-word podcasts. Processing software can easily convert your 16 or 24 bit PCM audio to 32 bit-float temporarily for digital processing and return it to 16 or 24 bit PCM format.