The seemingly never ending descending or ascending of pitches is an auditory illusion that can be reproduced with synthesized tones, superb acoustic orchestration or human voices. Albeit the human voice version of this experiment is a bit more tricky.
The vocal version requires a choir of at least 8-12 with full ranges, who is very skilled at overtone singing, to the point where they have great control over their dynamics. The reason for this is stated below:
My colleague and voice researcher Wolfgang Saus, explains:
“The effect is based on Jean-Claude Risset’s acoustic illusion. The formants are either fixed on /ɔ/ or alike, with first formant high, or second formant should rise continuously while the fundamental decreases. Towards the lower end of the glide the volume decreases and the voice starts softly with a high pitch again, each time ending a bit lower. The loudest part is always in the middle section of a glide.”
I will add to that, saying that collectively, the singers stagger their entries (seemingly at random) at the top end of the glide. This is what allows the illusion of the constantly descending pitch. Also, singers choose their own overtone to use each time, moving down in a parallel way, keeping the same overtone all the way down. Thus, each new entry may add a different ‘vowel’ sound to it. This further adds to the complexity of the harmonic texture of the sound overall.
In this piece of music, Arc Descents, composed by David Hykes, you will hear this effect starting at the 2:30 mark.
For a detailed explanation of what exactly occurs in a standard ‘Shepard tone’ sequence, please refer to the following Wikipedia pages: (Here you can also listen to audio examples)
Jean-Claude Risset on Wikipedia
For a splendid example of orchestration illustrating this effect, have a listen to Arvo Part’s Cantus in memoriam of Benjamin Britten
CommentMy good friend and overtone singing expert Wolfgang Saus has been researching the voice for over two decades. He has developed a brand new approach to the use of formants in singing, that is about to revolutionize the choral and classical singing world. He has even crossed the previously impenetrable barrier between western overtone singing and the opera world. So it is only a question of how the ‘twains’ shall meet. He recently related a story to me, of how a frustrated operatic tenor, who had a problem with his passaggio (transition from chest voice to head voice), frantically drove for 5 hours to meet with him. Wolfgang gave him simple exercises which solved this problem once and for all. The opera singer was gob smacked. He then went home and presented this new found knowledge to his fellow opera singing friends with similar issues. All were amazed.
He also told me that the IPA experts (International Phonetic Alphabet) were all mistaken when they claimed that only one possibility of a pattern of formants was responsible for any given vowel. And he’s got the proof.
So it is this new sensibility and new found cooperation between disciplines that I hope to bring your attention to. Where is this leading? To a disruption of the status quo? One can only imagine. As for me, as a professional overtone singer and composer of overtone choir music, I intend to be involved as a bridge in this scenario. It also means becoming more clever about writing lyrics with certain vowels on certain frequencies that can bring about the most effective results.
Here’s a link to a paper by Wolfgang Saus on this topic of formants, as it relates to Stockhausen‘s composition Stimmung.
Comment
