Audio Technology / Recording techniques/ Recording Environment...

Recording environment

Much of the success of a speech recording depends on the recording environment and microphone placement. Ideally, speech recordings should take place in soundproof studios or labs. If those are not available, one should try to find a relatively quiet room with as little low-frequency noise as possible. Most typical sources of low-frequency noise include 60-Hz hum from electrical equipment, heating and air-conditioning ducts, elevators, doors, water pipes, computer fans, and other mechanical systems in the building. If possible, those devices should be switched off during recording. The figure below illustrates the spectrum of a typical ambient room noise. The low-frequency prominence of this kind of noise may interfere with acoustic analysis of the fundamental frequency and the first formant. It is also quite difficult to filter out any such extraneous noise without removing information from the speech signal itself. High frequency noise should also be avoided, though it can be more easily filtered out of the signal before analysis.

Spectrum of typical room noise. Note the prominence at around 600 Hz.