Notes for Class No. 17

Lists Revisited and Introduction to Transposition and Assignment No. 6

loops and how they can be used to play all the notes from a list
“deltas” or “offsets”
- “delta” is the Greek letter Δ
- it is typically used to denote a change from one value to another
- in the context we’ve been talking about, a delta and an offset and a change are all the same thing
different ways to play music from a list in different keys
- by adding a delta or offset to the note value read from the list
- by reprogramming the list itself to contain deltas (or intervals) rather than absolute note values
different ways to use deltas in lists
- as offsets from the starting note (the first note of the piece)
- as offsets from the tonic note (the “key” note of the piece)
- as offsets from the previous note (the one that immediately precedes it in the list)

Starter Program

http://scratch.mit.edu/projects/19994891/

Here’s a link to the song

https://www.youtube.com/watch?v=A_MjCqQoLLA&t=0m55s

For those of you who read music, here is the score from which this was programmed

The important thing to look at is the list that plays the notes

the key is that lists can contain strings of characters (note designations in this case) and that one can use those strings in broadcast blocks
notice how there is a when I receive block for every possible entry in the Notes list, including a rest
also notice how the two sprites are used, and how an initialize stack is used to keep the main stack (the one that contains the loop) clean and short

What you are to do

use my work as a template to add a list of note (and rest) durations (the rhythm of the song)
use those list values inside the loop to set the BeatsToPlay variable before the broadcast block
test your work thoroughly and compare it to your neighbors’ solutions