Amplitude variations in commercial audio oscillators have been found to be of the order of 50 to 60 db below the amplitude of the oscillator fundamental output. In a companion paper these variations are considered with respect to their effect on psychophysical experiments, as in audition. This paper presents a summary of the sources of variation in amplitude and discusses their relative magnitudes and differences in spectra. The quantityN0, noise power per unit band width of white noise, is related to the amplitude spectra of the variations in oscillator output, and the spectral value at the oscillator average frequency is shown to be important as an equivalent noise power per unit band width in psychophysical experiments. Results of typical approximate measurement of this quantity are given. (This work was carried out under sponsorship of the Operational Applications Laboratory, Air Force Cambridge Research Center.)