Microphones and Room Acoustics and Their Influence on
- Slides: 14
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 • Microphones • SPL calibration • Room acoustics / Noise • Recommendations
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 • Omnidirectional measurement microphones can be flat within a d. B 20 -20 000 Hz • Microphones for stage/studio use often have a peak around 5 -10 k. Hz • Cardiod microphones have a distance dependent bass boost (proximity effect)
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 • A calibrator is a device that is attached to the microphone and generates a well-defined SPL (usually 94 d. B, 1 k. Hz) • 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 • 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 • 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 • 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
Room acoustics Recommendations • 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 1. Directional microphones suffer from a proximity effect, use omnidirectional microphones if possible 2. SPL calibration is cool 3. Voice SPL needs to be reported with a distance (e. g. 30 cm) 4. 30 cm is the smallest acceptable distance for sound level meters and microphones not fixed to the head 5. At distances larger than the reverberation radius, voice is always altered by the reflected sound
Big nonos • Measure H 1 -H 2 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”
Thank you!
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