Designed for general-purpose applications, the Model 412 audio attenuator and amplifier provides 80 dB of attenuation in four-decade steps, plus fine attenuation in each step with a single-turn potentiometer. The instrument delivers 40 dB of gain over five steps of x1, x10, x20, x50 and x 100 and a sine-wave output of 300 mVRMS, ±0.25 dB from dc to greater than 100 kHz. Output noise is up to 200 µVRMS at x1 gain with the input shorted and minimum attenuation, with the value increasing to 2mVRMS at a gain of x100. According to the company, the harmonic distortion added by the unit to frequencies from 1 Hz to 100 kHz is too low to measure. Other features include an input impedance of 10 k½ and an output dc offset of 200µV at x1 gain and 2 mV at x100 gain, measured with the input shorted and minimum attenuation. TDL TECHNOLOGY INC., Las Cruces, NM. (505) 382-3173.