Upon watching the results, I couldn’t resist to offer Marc some extra help with the post-processing of the recovered audio. I got in touch and he promptly sent me the audio file. I rushed to give it a listen and started working on it. I figured some processing could be done to remove some unwanted blemishes and improve the overall intelligibility of the recording. The process involved correction for pitch due to the machines’ transport mechanism variations, flutter, noise reduction, corrective EQ for compensation of the systems’ frequency response and a couple other things such as attenuating the “thumps” caused by the periodic pass of both tape creases due to the way it was stored. When dealing with artifacts like these, one can take advantage of what would in most cases be purely a technical issue. In this case, having a mains ground hum on the recording can be quite helpful to assert the correct speed of the tape since it fingerprints the original recording with a pilot tone that can be used to correct for variations on the playback speed, including wobble, flutter and the baseline tape speed. You can hear the resulting difference below.