I'm afraid my daughter wants no part in watching her Grandfather perform card tricks to prove his presence is genuine. She felt as sick as I felt when it was initially suggested.
Who is talking about card tricks? There are no tricks involved. Would you be insulted if someone who could only hear your voice asked you to present evidence that you are the one you claim to be?
I am begining to wonder what constitutes as a fair and respectful protocol to test a spirits presence, rather than using part-method of a protocol that has been constructed to test potential Psychic ability.
There is nothing psychic about the ability to tell what card you can see, at least if it is face up. If somebody asked me to tell the value of a card, I would not mind, nor hesitate. The whole point here is that the spirit should be able to see it, and you should not, but as you have found out, it does not work when you yourself do not see the card, so that is a strong hint that there is no actual spirit, but only you interpreting what is actually meaningless noise.
There was a clear message in his own voice last night, on a recording dated 18th Oct 2012 "We don't want cards tricks"
The fact that you and the spirit use the same choice of words also hint that there is no spirit, but only you.
Do you actually know what pareidolia is? It is not a mental illness but a normal ability to see or hear patterns where there are no patterns. We all have the ability to recognise drawings, even though these drawings are not the real thing. But fortunately for art and culture, we do see these patterns.
But we can also see the same kind of patterns in rust stains, toasted bread, and so on, even though they are just random stains. This is normal, but it does make the patterns represent something real.
Audio pareidolia work in the same way. We can sometimes hear familiar voices or noises in something that is really just random noises. People have found that if you play recordings backwards, you might hear all sorts of messages. These messages are not real, but examples of pareidolia. It has also been mentioned to you that often we cannot clearly hear something, and then we interpret what we hear. When we know that a choir piece is called "O Fortuna", we might hear "O Fortuna", but if somebody tells us that it is called "Oh Four Tunas", this is what we hear.
The reason why you can pick up an old recording of yours, and suddenly hear another message than you did the first time, is that there really is just random noise, and you are interpreting it to make sense. In the period since you made the recording, you have forgotten how you interpreted it the first time, and now you are making a new interpretation that more suits your present circumstances.
Just like with "O Fortuna" you can tell other people what there is to hear, and
they will hear what you said you heard. This is how pareidolia works, and this is why your daughter, your GP, and the other "witnesses" all heard the same thing: You told them what to hear.