# String of Yeasts

After reading and studying the data (so far) from The Sourdough Project, a bit of it jumped out as a possible sound pallete. The growth profiles of the five most prevalent yeasts and aabs (acetic acid bacteria) measured as increasing Optical Density over a 48 hour period. Measurements were taken in 12 hour increments and recorded from 0.1 to 1.2 levels of density.

I was drawn to this data because the graphs reminded me of waveforms.

I am not at liberty to reveal the details of the data, so suffice to say that these are 5 strains of yeast. We will call them pink, blue, orange, green and neon. The pinpoints mark the 12 hour samplings of the prevalence of the strain. So at 12 hours pink grew to around .25 OD, while neon grew to .6 OD. How to represent this in sound is the next question!

My old friend, the piano keyboard, provides a familiar sonic framework. A two octave chromatic scale will represent the sound of OD growth by stretching the OD measurement scale over the two octaves. Like this:

Each OD amount covers 2 notes. D and D# represent the .1 amount, E and F are .2 and so on. This allows some wriggle room when the 12 hour sample seems to be between two numbers as is seen with pink. The growth range for pink will run from D to F and encompass 4 notes. In the case of neon, the growth range runs from D to C and encompasses 11 notes. The differences in the growth rates will be heard in the number of and duration of the steps taken within each twelve hour time frame. So far, so good!

The time frame will run in beats and measures. Since it is 48 hours of growth, one hour can equal one measure. The step patterns will run up to the highest note indicated by the OD data at that particular 12 hour marker. That makes each sampling unit 12 measures in length – seems perfect. Even better, at 4/4 time, each 12 measure sampling unit is 48 beats long! Synchronous!

Lets lay out the first 12 hours of pink and neon. Since all the yeast densities begin from .1, all the patterns will begin with D in the 3rd octave (D3). pink grows from D through D#, E, and lands on F. For this growth pattern there are 4 notes and 48 beats, so each note will be 12 beats long. The long notes and fewer steps up communicate that pink did not grow much in the first 12 hours. Neon grows from D, D#, E, F – C. For this growth pattern there are eleven notes and 48 beats. Each note is 4.36 beats in length. So the first ten notes are four beats long, and the eleventh is eight beats. The longer note at the end places emphasis on the final growth number for that 12 hour period. Faster steps further up the scale sonify neon‘s more abundant 12 hour growth period.

Looking at the graph, it is easy to hear that the growth patterns of pink and neon invert at the 12-24 hour sampling unit. Pink leaps from .25 to .7, while neon short stretches from .6 to .75. Again, note duration and number of steps will sonify these contrasts in the data.

While a sense of growth is captured by the movement up the scale, there is not yet a sense of increasing density. To get at this, I decided to sustain the top note of each 12 hour sampling unit. As example, pink’s F and neon’s C would continue softly to the end of the 48 measures. This would follow for the last note of each 12 hour cycle and will create the sense of sonic density.

Enough talk, lets have a listen!

neon 48 hour growth pattern

pink 48 hour growth pattern

These are the 48 ms versions of the patterns. So 48 4/4 measures at 120 BPM really stretches out these relationships making it harder to hear the movement of the data. Ableton Live has a function that allows me to collapse the sequence from 48 measures to 24 measures and still maintain the rhythmic integrity of the phrase. WoW! Then the phrase can collapse to 12 measures. All of these phrases will likely be a part of the Sourdough Song, but I am still deciding which version (24ms or 12ms) conveys the data more clearly. One of the researchers on the project said the longer growth articulations conveyed the anticipation the bakers feel as they wait for their starters to grow.

Here is the 12 ms version of both strains together. See if you can hear the changes described above. Listen closely for each voice – you will hear pink holding longer tones, while neon changes tone more quickly. It helps to look at the graph while you listen.

This will likely be one a motif within The Song of Sour Dough. (What do you think of separating sourdough in the title?)