Spectrum Analyzer and Equalizer

The circuit shown in Figure 1 uses only two ICs, and has a bandwidth that is adjustable from more than one octave down to a tenth of an octave. As shown, the frequency range is 20 Hz. to 20 KHz. in three bands, although a fourth subsonic band could be added to allow very low frequency analysis. A low-noise mike preamplifier is included, and a line input is also available with up to 20 dB of gain. Of course, you could use a mike preamp in your console instead, but at the expense of portability.
Spectrum Analyzer and Equalizer - schematic

Selecting a suitable measuring microphone is crucial for serious room analysis, since no doubt the mike will be the weakest link in the measuring chain. First, it should be omni-directional because reflections off walls, ceilings and floors contribute gre

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