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I remember that a german electronic issue called elektor has had such an article including schematic and layouts. This was about 10 years ago. Perhaps you'll find something on their homepage. The article was called 'Audio Terz Analyzer' or similar.
It was in 1984 and called "Terts-analyzer" and published in three parts March page 54..., April page 56... and May page 34...
There was an other article called "Spectrum Analyser" a 10 bands, published in Electronica Top Internationaal a Dutch magazine, not available onymore, November 1978 page 10..
I can find many software programs on the web, but I want hardware.