audio - problem solving: line level to iphone attenuator buzzing

I'm trying to use the mic input on my iPhone to record line level audio. I have made a cable with an attenuator as shown in the picture below. Recording from my macbook pro works like a charm (3,5mm

Are there any viable/accurate apps for metering db exposure? This is for hearing safety related to drumming & performing rather than mixing for a show, but I figured the people here might

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