They may look pleasant enough, but they can add a horrible hum to your recording. Never, under any circumstances, plug your recorder or other related electronic equ ipment into an AC circuit controlled by a rheostat. • By the same token, beware of air conditioners, refrigerators, and fluorescent and neon lights; these also are sources of electronic noise and hum. If you get lazy or forgetful and allow the oxide deposits to build-up, performance will suffer noticeably—especially high-end respon