What is the ‘plus’ and the ‘minus’ after each musical note?
/A cent is a unit of measure for the ratio between two frequencies. An equally tempered semitone (the interval between two adjacent piano keys) spans 100 cents by definition.
As you will notice each of the bowls is described by a letter that donates to a musical note. The easiest way to visualise this is on the notes of a piano.
As you will see the white keys and the black keys take you through the 12 notes in an octave. The space in-between each note ie: between A and A# is called a semitone.
Within each semitone there is a movement of sound from one note to the next. The ‘cent’ is a unit of interval measurement within the semitone and it is exactly 100 equal parts.
So if for example, we have a middle octave ‘A’ note (Usually a 7 or 8 inch bowl) and a middle octave ‘A#’ note, the space between them is divided into 100 equal cent. On our sound measurements it looks like this:
A0 - This is a ‘true tone’ note tuned to the 440Hz.
A+5
A+10
A+15 - This cent interval is tuned to the 528Hz
A+20
A+25
A+30
A+35
A+40
A+45
A+50 / A#-50 At the point we are exactly half way between the mid octave note of a A and A#
A#-45
A#-40
A#-35
A#-30 - This cent interval is tuned to the 432Hz
A#-25
A#- 20
A#-15
A#-10
A#-5
A#0
When choosing bowls that harmonise with each other, the desired distance between the notes is at a maximum movement of 20 cent . For example a collection of Alchemies in notes that all range between ‘-20’ and ‘-40’ cent. Musicians who are playing the bowls with other instruments may choose to have exactly the same pitch on every bowl ie: ‘0’ (True tone to 440hz).
I would also urge you to read my blog about harmony to understand a little more about how we are breaking into a new understanding of musical theory. An awakening chorus of crystal sound that doesn’t always behave in the same way as we have perceived most musical instruments in our history.
There is another way of measuring the frequency in the note through the unit of Hz.. That is for another blog.