There are many reasons why an instructor might choose to record a seminar or lecture: Perhaps there's a desire to provide lecture material for absent students. Maybe there's interest in developing a podcast for online instruction. Perhaps there's a desire to capture questions or feedback from the audience in real-time for later review.
Whatever the case might be, there are many ways to record speech, and the technology exists today to create a professional sounding recording without spending a lot of money.
A few years back a typical podium setup would include either the ubiquitous unidirectional microphone mounted on the podium or a lavalier (or lapel) type worn by the lecturer. The advantage to the podium setup is simplicity and excellent audio reproduction, the downside is the loss of mobility as the speaker is effectively tied to the lectern.
A wireless lavalier (or lapel) microphone is a better option for mobility or hands free operation, but the disadvantage here is that the speaker is the only one amplified. Lavalier microphones typically come in different polar patterns including omnidirectional, but the depth of field is reduced to eliminate ambient noise. When using a lavalier microphone it's virtually impossible to capture audio from the audience.
The typical way to get around these limitations would be to have someone walking around with a wireless mic to field audience questions, or to install a microphone array. An array is essentially a group of vocal microphones working in tandem and strategically placed throughout the room. These mics would then be attached to a computer so that the signals can be collected and assembled into a coherent form. This is a good solution in that both the lecturer and the audience can be recorded, but there's a tradeoff in the complexity of the setup.
The newest array microphone technology addresses these limitations. It's now possible to have a number of closely spaced vocal microphone elements located within the same device. Given the fixed position of each element, digital signal processing (DSP) of each signal source can create "virtual" microphones with complex virtual polar patterns that provide the ability to zero in on, or to reject particular sound sources.
This is the best possible choice for lecture recording as these types of microphones can find and isolate a moving speaker while filtering out background noise and reverberations (think air conditioning) typically present in classroom settings. One example of a mic that uses this technology is the Voice Tracker Array Microphone [http://www.vocal-microphones.com/p55-101-Voice-Tracker-Array-Microphone.html] by Acoustic Magic.
This particular mic uses the newest generation technology allowing it to locate and follow the speaker as he moves about the room. The patented noise reduction algorithms give the mic an effective range of 30+ feet which is ideal for a typical classroom setting. With one microphone it's now possible to cover all participants in the room as the "listening beam" can move from one talker to the next in milliseconds.
Vocal microphones such as this one can be directly connected to a computer, integrating easily with standard software for the editing and packaging of the audio content.
Hopefully this article was helpful in explaining some of the technologies available for lecture recording. If you're looking for a single mic that can cover both the speaker and the audience, the newest array microphones are a good choice.
