from jensens website synopsis of the paper:
Jensen transformers improve signal quality by removing hum, buzz and interference signals of other types (such as radio frequency interference) from the audio signal. The Bessel low pass filtering effect also removes ultrasonic distortion products generated by previous amplification stages from the audio signal. These ultrasonic distortion products create additional intermodulation distortion products when amplified by succeeding stages. These signals are folded back into the audible frequency range, generating an audio modulated, non-harmonically related noise floor. This type of noise is characterized by listeners as a "veil" in front of the music. The term "Spectral Contamination" was coined for this effect by Deane Jensen and Gary Sokolich in their 1988 AES Paper titled "SPECTRAL CONTAMINATION MEASUREMENT". Copies of this paper are available from the Audio Engineering Society and from Jensen Transformers, Inc
Tom,
so we have to be careful as always about audibility of folded back distortions, ie if they are 120db down to start with and we fold them back and they are still 110db down can it be heard in a normal listening situation