RMS-to-DC for Sound Pressure Level measurement

Hi,

I want to measure the RMS value of a microphone's output voltage (to get the SPL value in dB).

I see a lot of RMS-to-DC IC seem to do that but I am wondering :

At a given moment, if I read the output of the RMS chip (on an ADC), is the RMS (the average/mean part) calculated on the last 10ms ? 100ms ? 1sec ?

In other words, I want to read the RMS value every second. So I want it to be representative of the last second that just passed not the last 10ms.

How is it related to the "settling time" parameter (if it is) ?

Best regards,

V.

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  • 0
    •  Analog Employees 
    on Jan 29, 2016 7:59 PM

    The AD737 averages the rms over a fixed time period as you surmised.

    ADI makes parts for audio applications such as you describe, I believe you are looking for the 'dB output' feature, where the log of the input is provided as a current sourced output. You can apply it to any decent low-distortion op-amp configured as an I-to-V converter. The part numbers are AD536A, AD636 or AD637. Any of these three will provide the feature you're looking for.

    Best,

    js

Reply
  • 0
    •  Analog Employees 
    on Jan 29, 2016 7:59 PM

    The AD737 averages the rms over a fixed time period as you surmised.

    ADI makes parts for audio applications such as you describe, I believe you are looking for the 'dB output' feature, where the log of the input is provided as a current sourced output. You can apply it to any decent low-distortion op-amp configured as an I-to-V converter. The part numbers are AD536A, AD636 or AD637. Any of these three will provide the feature you're looking for.

    Best,

    js

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