One of the big challenges for research on physical mediumship is that many phenomena are occuring only in low-light conditions or in complete darkness. Rather than reiterating the common demand of psi researchers to install infrared cameras as prerequisite for any type of research, here a different approach is taken, using audio recordings. With an appropriate setup of microphones and some postprocessing, it is possible to get some interesting information about what is going in the darkness

Forensic voice analysis for mediumistic phenomena


Many thanks to Warren and his spirit team to allow and support these investigations! Also many thanks to Lucius Werthmüller from Basel Psi Association for acquainting me with the area of physical mediumship (which, of course, initially sounded totally weird to me), for establishing the contact with the medium and for many interesting discussions about psi research.


Sound source localization in séances with Warren Caylor

Motions of ectoplasm / 'voice box'


At the end (and sometimes also at the beginning) of the appearance of the spirit voices, a throaty sound can be heard, which is moving quite rapidly. Supposedly, the direct voices are generated by an ectoplasm 'voice box', on which Yellow Feather commented during a home circle:


'Eckhard, you may find the sound of the ectoplasm, when you plot it, your graph will change in height as it travels. That is because when it is extruded it goes up and then down to the floor. When it goes back, it comes back up off the floor into the air and back down towards the channel. So if you see some unusual changes in height from the sound of ectoplasm, that is why.'


So, here are the graphs of such motions (each one lasting one to two seconds). The arrow heads indicate the direction of motion. Keep in mind that only the audible part of the motion could be captured.

Forensic voice analysis for mediumistic phenomena....


The typical task in forensic voice comparison is to analyse and compare speech samples in order to decide whether a suspect is identical with the offender. By comparing the voice samples with each other but also with other voices, a likelihood ratio is calculated: What is the probablity that suspect and offender voice are the same versus the probablity that the offender voice can come from somebody else.


To provide evidence for or against the originality / authenticity of mediumistic spirit voices, this approach has to be adapted somewhat. Especially, it has to take into account that a medium trying to fake a spirit voice will probably not use his own natural voice but will try to feign a voice which sounds different. For example, it is quite easy to shift the pitch of the voice to sound differently. Thus the pitch (technical term: the fundamental frequency) of the voice will typically only provide very weak evidence. Of much more interest are some overtones in the voice, the so-called formants, which depend on the vocal tract - its anatomical shape as well as (mostly unconscious) patterns how it is changing with the tongue, mouth, oral and nasal cavities when speaking. In contrast to forensic voice comparison, which often has to rely on low-quality audio recordings, such as from telephone communication, séance phenomena can be recorded with high-quality audio, thus also making the higher formants, especially F3, F4, available for analysis.


The following picture gives an example (spirit voice Albert). On the left hand side, it shows how often formant F1 and formant F2 appear in a certain relation to each other. The F1-F2-combination is the main factor to distinguish between the sound of different vowels (rough average positions of some vowels are indicated), but it also depends on the individual speaker. In the middle, the picture shows the distribution of the combinations of the formants F3 and F4. They have a higher frequency and do not matter for speech recognition, but can be relevant for distinguishing different speakers.

A first question to address skeptics is: How likely is it that the medium is capable to fake the various spirit voices heard during a séance - taking into account that the medium purposely may try to force his own voice to sound different.


Here are the graphs of some other spirit voices appearing in Warren's séances:

Already the visual appearance shows a lot of differences. (For those who know Luther's very low voice: The very high fundamental frequencies in the diagram are a problem of the pitch detection algorithm when dealing with Luther's special, mostly unvoiced pronunciation, which may as well be somewhat below the detection pitch range).


To further illustrate the different profiles of the spirit voices and Warren Caylor's own voice, here the F3-F4-distributions are shown in a single 3D view: