playing back such recordings at a constant speed can make speech much more difficult to understand and has obvious dire effects on the reproduction of music. Fortunately, several phonautograms had a separate parallel track, inscribed simultaneously with the voice track, in which a constant reference tone had been recorded. By working with short segments of the paired tracks and adjusting both so that the reference tone was held to a steady pitch, it was possible to correct the irregularity and greatly improve the results.