Spectrum Analyzer & Resonance

[Lord Theo]

In addition to resonant acoustical 78's, I'll occasionally run across an lp that sounds as if it's been recorded in a shower stall. How is the frequency of these resonances displayed on the spectrum analyzer?

[Craig Maier]

It will look like a Gaussian distribution (sometimes called a "Normal" or "Bell" curve). It can be either upwards deflecting or reverse deflecting (as in the case of an anti-resoance). It is usually less than an octave in width. It takes a bit of training to see these things and to be able to distinguish them from the normal peaks and valleys in the overall response of a recording. But, generally, these bumps or dips are larger in amplitude than any of the musical variations that one would find on most recordings. Also, there can be smaller bumps riding on top of the resonace (or anti-resonance).

[Lord Theo]

Thanks Craig.....I've "analyzed" several recordings & seemed to have found a pattern....high amplitude bumps in an otherwise normal looking display, almost like acne. My acoustic recordings have them in the 300-500 hz range. Rudecing or eliminating them has very positive results.

[Craig Maier]

Assuming that you are using the Spectrum Analyzer method for average spectral measurement, you can point your mouse at the peak of these resonance(s) and left click on them and it will display the frequency and amplitude of the spectral bump in the upper left hand corner of the Spectrum Analyzer display. That will make it easier to set up the pargraphic or 20 or 30 band graphic EQ to compensate for it.

Note: For more information on this topic, refer to this link:

http://www.diamondcut.com/vforum/showthread.php?t=2620

[Lord Theo]

yes...I especially like using paragraphic as the exact peak of the bump can be easily set & the balance of the bump tapered, sort of a reverse bump.....hope I'm making sense, thanks again.

[Craig Maier]

Yup! The paragraphic EQ is the ideal tool to use in this particular application.