Measuring Digital MEMS Microphones
Frequency, Sensitivity and Power Supply Rejection (PSR) Performance
This test suite contains 3 sequences to enable comprehensive testing of digital MEMS microphones:
- Measurement of frequency and sensitivity using a calibrated source
- Measurement of frequency using the ‘substitution method’, a solution for measuring frequency response where the source speaker cannot or is not equalized
- Measurement of power supply rejection (PSR) performance
Digital Microphone: Frequency and Sensitivity
This sequence demonstrates the two most common ways digital MEMs microphones are measured: frequency response and sensitivity. A stepped sine sweep is played from 10kHz to 100Hz through a source that has previously been calibrated to produce 1 Pascal across the frequency band. The recorded signal is analyzed with a HarmonicTrak analysis step, which calculates the response curve. A post processing step is then used to extract the sensitivity value at 1kHz. Limits are set around both the frequency response and the sensitivity, the default values are for a typical MEMS microphone and should be adapted to your device.
The final display shows two graphs. The top X-Y graph displays the data at its absolute level in dBFS. The lower graph shows the same frequency response curve but normalized to 0dB at 1kHz. This is a common way of displaying microphone frequency response and applying limits.
- SoundCheck 18.0 Basic or later
- Portland Tool & Die DCC-1448 (Listen p/n 2018) or PQC-3048 (Listen p/n 2018)
- AmpConnect (Listen p/n 4042), SC Amp (Listen p/n 4060) or other power amplifier
- Source Speaker
- Measurement microphone e.g. Listen SCM3 (p/n 4002) and any required power supply e.g. (Listen SoundConnect 2 p/n 4025 & 4026)
Hardware Setup and Calibration
- Calibrate your microphone and the source speaker as per the instructions in the SoundCheck manual
- Connect the MEMS microphone and digital MEMS interface per Digital Microphone Test Configuration Notes.