Unit of measure for the MEMS IMP23ABSU microphone

[TomRett]

Hello, i have searched for this information, but couldnt find it anywhere. Whats the unit of the measured of the MEMS IMP23ABSU mic? I have used the STEVAL-STWINKT1B with the FP-SNS-DATALOG1 from which i created several .csv files that i now need to analyse. I have exported the values as "raw values" (which is an option you can choose when running the script of the dataloger).
So far i have checked the DeviceConfig.json from the dataloger and found out that the unit is  "unit": "Waveform". Does that mean the values, measured from the microphone, are in Pa or dB?

You can find part of my DeviceConfig.json below.

{
                "id": 7,
                "name": "IMP23ABSU",
                "sensorDescriptor": {
                    "subSensorDescriptor": [
                        {
                            "id": 0,
                            "sensorType": "MIC",
                            "dimensions": 1,
                            "dimensionsLabel": [
                                "aud"
                            ],
                            "unit": "Waveform",
                            "dataType": "int16_t",
                            "FS": [
                                130
                            ],
                            "ODR": [
                                8000,
                                16000,
                                32000,
                                48000,
                                96000,
                                192000
                            ],
                            "samplesPerTs": {
                                "min": 0,
                                "max": 1000,
                                "dataType": "int16_t"
                            }
                        }
                    ]
                },
                "sensorStatus": {
                    "subSensorStatus": [
                        {
                            "ODR": 192000,
                            "ODRMeasured": 192000,
                            "initialOffset": 0.19303,
                            "FS": 130,
                            "sensitivity": 1,
                            "isActive": true,
                            "samplesPerTs": 1000,
                            "usbDataPacketSize": 4096,
                            "sdWriteBufferSize": 136192,
                            "wifiDataPacketSize": 0,
                            "comChannelNumber": -1,
                            "ucfLoaded": false
                        }
                    ]
                }
            }

[TomRett]

Thanks, but that doesn't answer my questions. 

What sensitivity values does the DeviceConfig.json accept ("sensitivity": 1)?

Is the sampling frequency defined with "ODR": 192000, "ODRMeasured": 192000 ? What is the connection and the difference between ODR and ODRMeasured? 

[SimonePradolini]

Hi,

Excuse me, I lost some of the questions in the long thread.

Sensitivity is only a readable value, you can't set it.

ODR and ODRMeasured as separated values. They described the nominal and the real measured data rate value for each sensor.

The greater part of MEMS sensor has each own resonator with no timing synchronization with the MCU. So, there could be the possibility that sensor clock drifts, and there is no control on the difference between the sensor master clock and the MCU clock. In this situation, setting a nominal ODR can generate a real ODR drifted about 3-5%.

This is not the use case for microphones, where no internal resonator is needed. To let the microphone working it exposes a pin for linking directly a clock from the MCU. So, by design, there is no clock drift between the microphone and the MCU and ODR and ODRMeasured are exactly the same.

[TomRett]

Thanks you! I receive a shorter amplitude range when i set the ODR from e.g. 192000 to 32000. Why does this happen? Here is the same procedure with ODR: 192000, ODRMeasured: 192000

 and below with ODR: 32000, ODRMeasured: 32000

 

 

[SimonePradolini]

Hello,

We are working on patch releases for both FP-SNS-DATALOG1 and FP-SNS-DATALOG2.

By looking at your requests we found a bug in the software microphone setup we'll solve in those releases.

Updated versions should be online in a couple of weeks. I suggest to update the package and eventually come back with your further feedbacks.

Best regards

[TomRett]

What is the bug? I am working with the mic on a daily basis and all my measurements depend on it.