Songs were recorded with a Sony tape recorder (models TCM-5000 and TC D5PRO II) and a Sennheiser microphone (model
K3U), and analyzed by means of a Kay Sonagraph (model 6061A) or Kay Elemetrics model 5500 and a Krone-Hite model 3550 filter with high (7.0 khz) and low (1.0 khz) settings.