Here is an outline of how to play multi-phonics (Mp) on the cello
(theoretically these can be applied to violins and violas but I have found it to be much more difficult to get those tiny strings to react in the same vibrant way that a cello or a bass might… so apply these concepts to other instruments at your own risk!!!)
Things to keep in mind while exploring:
1.) Mp's are created when the finger splits the string in between two natural harmonics in the strings overtone series: always use harmonic finger pressure!
2.) The accidentals used are simply to relay vague geographical locations on the instrument for where the finger (playing the Mp) should be placed. (to be more precise, follow the number indications of the partials that these Mp's lie between, and allow the player to find it for themselves)
3.) The bow is an equally vital part in creating the Mp. For each instrument, precise bow placement will vary. What I have indicated are general directions of whether it should be played towards the bridge or the fingerboard, but the exact point must be found by the player.
4.) Bow pressure is also extremely important. By changing the bow pressure you can get the entire Mp to sound or only wavering parts of it. Players must also experiment with this as the weight of the bow and the density of their strings will effect the resultant sound. again, there are no absolutes.. just try it out!
5.)I did not make any attempt to use a specific notation method when dealing with accidentals and quarter tone markings… there are just too many of them out there and I think that they all have some use
6.) The ones that work the best in my opinion are the Mp's between partials 3-5, and 6-7 on each string, I think they have the most "electronic" sound quality… The Mp between the 4-5 partials is especially difficult to get, but when its there, it is very satisfying!
7.) This WILL be frustrating to players, but once practiced can be performed with totally dependable accuracy… just like any other contemporary extended technique! :)
***also I suggest listening to the following video clips on head phones, sometimes the Mp's are quite subtle in their differences***