Microphone placement
The placement of the microphone directly affects the intensity of the recorded signal as well as the signal-to-noise ratio. The inverse square law guarantees a loss of approximately 6 dB per doubling of distance from the sound source. A typical handheld microphone is usually placed at a distance of 30 cm or so from the talker's lips. This, relative, to a close placement (say, 4 cm) represents the loss of about 18 dB and an increased possibility of noise leaking into the recording. For this reason, it is recommended to use a head-mounted condenser microphone (such as AKG C410 or AKG C420) to maintain a close, and constant distance to the source. Speech signals acquired this way are characterized by a high SNR and a broad range of intensity. It may also be useful to use a linear phase high-pass rumble filter (60 Hz cutoff and 24dB/octave attenuation), unless low-frequency components are expected in the signal.
