I am using an LM3915 to build a VM meter for monitoring recording audio.
The data sheet shows 4 LEDs light when ≈1.2V is applied. I attached an audio signal from my laptop using a 1/8" stereo to RCA cable that was plugged into panel mount RCA jacks with wire leads coming off. When I attached my voltmeter to the leads, I got an AC that maxed out at ≈481mV. However, when I plugged the lead into my LM3915, I had 3-5 LEDs lighting with varying brightness as the music fluctuated.
How is this occurring when it is well below the data sheet specified 1.2V? Is the LM3915 actually showing the correct dB level even though the voltages vary? Additionally, the audio on my computer is maxed out, and quite loud from its speakers, but I am only getting the 480mV. How can this be the case?