Meeting Recorder: Near vs. Far Field Microphones

The following demonstrates the problems associated with near field (e.g. head-worn) microphones vs. far field (e.g. table-top) microphones for speech recognition.

As part of the Meeting Recorder Project, we have recorded several real meetings using many microphones, including head-worn and table-top microphones.

The figures below are waveforms and spectrograms of the same utterance, one recorded from a head-mounted microphone, and the second from a table-top microphone. The time axes are labeled in seconds. The recordings have been time-aligned to make it easier to compare the figures.

The far field recording, which was originally much quieter than the near field recording, has been amplified to make the average energies of the two recordings about equal. It has also been high-pass filtered to attenuate strong low frequency (below 120 Hz) background noise, which may have been picked up from the meeting room's air conditioning system.


Waveform from the near field microphone.

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Waveform from the far field microphone.

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Spectrogram from near field microphone. Notice the bright peaks and sharp transitions.

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Spectrogram from far field microphone. Notice the more diffused energy and blurred transitions.

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