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I have to design a spectrum analyzer that takes a normal audio input and creates a 4 band spectrum display.

My current plan to accomplish this task is to construct 4 band pass filters centered around the 4 frequencies that must be visualized. The audio input will be split into 4 identical signals via the use of 4 voltage followers (So as to ensure that they do not effect each other). These 4 signals are then each fed into a separate band pass filter. These filters then feed their output into a TI LM3915, which compares the input voltage against a reference voltage and then turns on between 1 and 10 of the output's. These are then fed into DIL Bar Leds for visualisation.

My question is: Does this seem like a legitimate method for accomplishing this, or am I way off the mark? And if it is a legitimate method, what improvements/flaws do I need to take a look at?

Side Note: I've seen the MSGEQ7 chip, however I have 4 specific frequencies that my analyzer must be centred around, so if anyone knows of an IC that can do this it would be even better.

Side Note 2: I can't supply a PCB schematic as this is for assessment.

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    \$\begingroup\$ Seems fine to me. \$\endgroup\$ – Scott Seidman Aug 8 '15 at 14:40
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    \$\begingroup\$ You might want to add a precision rectifier and peak detector with selected decay time. There's a schematic of one option on the LM3915 datasheet. \$\endgroup\$ – Spehro Pefhany Aug 8 '15 at 14:44
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You might want to take a look at this hackaday post http://hackaday.com/2014/01/03/build-an-audio-spectrum-analyzer-the-analog-way/ as he basically seems to have implemented your identical idea. The comment thread in particular has plenty of different implementations to experiment with.

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