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Microphones and Room Acoustics and Their Influence on Voice Signals . Svante Granqvist 1 , Jan Švec 2 1 Department of Speech, Music and Hearing (TMH), Royal Institute of Technology (KTH), Stockholm, Sweden

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microphones and room acoustics and their influence on voice signals

Microphones and Room Acoustics and Their Influence on Voice Signals

Svante Granqvist 1, Jan Švec 2

1 Department of Speech, Music and Hearing (TMH), Royal Institute of Technology (KTH), Stockholm, Sweden

2 Groningen Voice Research Lab, Department of Biomedical Engineering, University of Groningen, The Netherlands

recording voice
Recording voice
  • Microphones
  • SPL calibration
  • Room acoustics / Noise
  • Recommendations
microphone directivity
Microphone directivity
  • Two common directivity patterns
    • Omnidirectional
      • Picks up sound from all directions
    • Cardioid
      • Mainly pics up sound from the front of the microphone; good for suppression of ambient noise and reverberant sound
  • Omnidirectional is preferrable unless ambient sound is a problem
microphone frequency response
Microphone frequency response
  • Omnidirectional measurement microphones can be flat within a dB 20-20 000 Hz
  • Microphones for stage/studio use often have a peak around 5-10 kHz
  • Cardiod microphones have a distance dependent bass boost (proximity effect)
microphone recommendations
Microphone recommendations
  • First choice should be an omnidirectional electret or condenser microphone
  • If ambient noise or reverberation is a problem
    • Consider using a head mounted omnidirectional microphone
    • Consider a directional microphone
      • at least 30 cm from the mouth or,
      • at the distance which gives flat response
  • Make sure that you fully understand the consequenses before using head mounted directional microphones
  • Do not use dynamic microphones
spl calibration calibrator
SPL calibrationcalibrator
  • A calibrator is a device that is attached to the microphone and generates a well-defined SPL (usually 94 dB, 1kHz)
  • Standard for measurement microphones
  • Make sure the calibrator fits tight on the microphone
  • Never, ever use it for directional microphones!
spl calibration loudspeaker level meter
SPL calibrationloudspeaker & level meter
  • Generate a test tone with a loudspeaker or use a sustained vowel
  • The level at the microphone is measured by a level meter close to the microphone
spl calibration level meter at 30 cm mic at mouth
SPL calibration Level meter at 30 cm, mic at mouth
  • Can be used for headmounted microphones
  • Automatically accounts for the short distance between mic and mouth
  • Results in calibration as if level had been measured at 30 cm
spl calibration recommendations
SPL calibration Recommendations
  • Take the time to do level calibrations!
  • A simple calibration with the voice and a level meter is often enough
  • Calibration is not difficult, still it often goes wrong
    • Keys to successful calibration:
      • Verification
      • Experience / establisment of a standard procedure
room acoustics recommendations
Room acousticsRecommendations
  • Use an acoustically treated room to reduce reverberation
  • Put the microphone well inside the reverberation radius
  • Put the microphone even closer for soft voice
  • Beware of reflective surfaces
five points to bring back home
Five points to bring back home
  • Directional microphones suffer from a proximity effect, use omnidirectional microphones if possible
  • SPL calibration is cool
  • Voice SPL needs to be reported with a distance (e.g. 30 cm)
  • 30 cm is the smallest acceptable distance for sound level meters and microphones not fixed to the head
  • At distances larger than the reverberation radius, voice is always altered by the reflected sound
big nonos
Big nonos
  • Measure H1-H2 with a head mounted cardioid microphone
  • Record LTAS of the voice using a microphone at a distance of 2 metres
  • Use a calibrator on a directional microphone
  • To say: “I don’t need SPL calibration for this specific study”
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