inverting rows and making matrices
DESCRIPTION
This is important.TRANSCRIPT
On 1) inverting a 12-‐tone row
and 2) creating a matrix
This document describes how to determine all of the 48 row forms of a twelve-‐tone row. It does this in two steps. The first step explains how to invert a given row. The second explains how to create a 12 x 12 matrix (a matrix is a repository of all possible row forms for a given row). 1) Inverting a row Basically, an inversion is a mirror image. When we invert a row, we take the interval between each adjacent pair of pitches and change its direction. That’s right. The thing to remember is that when intervals are inverted, they keep their value but change their direction. Let’s take a simpler series of just four pitch classes: 3 E 8 1 . If we visualize them on the clockface, we should be able to find the shortest distance between each pair of pitches (‘directed interval classes,’ if you will). From ‘3’ to ‘E’ is minus 4 From ‘E’ to ‘8’ is minus 3 From ‘8’ to ‘1’ is plus 5 Now the easiest approach to inverting the series simply involves changing the directions of those intervals we just got. ‘3’ plus 4 is ‘7’ ‘7’ plus 3 is ‘T’ ‘T’ minus 5 is ‘5’ So, the inverted series is 3 7 T 5. If you apply that approach to the following twelve-‐tone row, P8… -‐5 -‐1 -‐4 +3 -‐4 -‐2 -‐1 +5 +1 +5 -‐1 8 3 2 T 1 9 7 6 E 0 5 4 …you’ll get I8 8 1 2 6 3 7 9 T 5 4 E 0. +5 +1 +4 -‐3 +4 +2 +1 -‐5 -‐1 -‐5 +1
2) Generating a matrix To generate a matrix for the same row, you’ll need to present the prime row horizontally, with the inversion of the prime running down the left side (as below). Make the initial pitch classes of P8 and I8 overlap. 8 3 2 T 1 9 7 6 E 0 5 4 1 2 6 3 7 9 T 5 4 E 0 Next, you must understand that when the matrix is complete, all of the ‘P’ forms will read from right to left. So, to complete the matrix, simply transpose the first row (in this case, ‘P8’) across each horizontal line in the matrix. You’ll need to use each pitch class from I8 as the initial note for each new transposition of P8. For example, the second line will be P1, a transposition of P8. Since pitch class 1 is five semitones up from pitch class 8, we must transpose all of the pitch classes from P8 up 5 semitones in order to generate P1.
The matrix below illustrates. Here, the row beneath P8 is P1. 8 3 2 T 1 9 7 6 E 0 5 4 1 8 7 3 6 2 0 E 4 5 T 9 2 6 3 7 9 T 5 4 E 0 In the same way, we can generate each new P-‐form by transposing the line above it. The distance between the first pitch classes in each row (given by I8, stated vertically) tells us what interval to transpose by. To derive from P1 to P2, we simply transpose each pitch class from P1 up a semitone. To derive from P2 to P6, we’ll have to transpose each of the pitch classes from P2 up four semitones. See below. 8 3 2 T 1 9 7 6 E 0 5 4 1 8 7 3 6 2 0 E 4 5 T 9 2 9 8 4 7 3 1 0 5 6 E T 6 1 0 8 E 7 5 4 9 T 3 2 3 7 9
Continue filling in the P-‐forms until your matrix is completed. One indication that you’re on track will be that the first pitch class of your first P-‐form makes a straight path through the matrix from the Northwest corner to the Southeast corner. (Of course, it’s still easy to make other silly mistakes with so much addition and subtraction along the way, so remember to check your work.) When you’ve filled in all of the P-‐forms, your matrix should look like this: 8 3 2 T 1 9 7 6 E 0 5 4 1 8 7 3 6 2 0 E 4 5 T 9 2 9 8 4 7 3 1 0 5 6 E T 6 1 0 8 E 7 5 4 9 T 3 2 3 T 9 5 8 4 2 1 6 7 0 E 7 2 1 9 0 8 6 5 T E 4 3 9 4 3 E 2 T 8 7 0 1 6 5 T 5 4 0 3 E 9 8 1 2 7 6 5 0 E 7 T 6 4 3 8 9 2 1 4 E T 6 9 5 3 2 7 8 1 0 E 6 5 1 4 0 T 9 2 3 8 7 0 7 6 2 5 1 E T 3 4 9 8 As each P-‐form runs from left to right, each R-‐form runs from right to left. Similarly, each I-‐form runs from top to bottom, and each RI-‐form runs from bottom to top. Remember, we label all R and RI forms by their ending pitch classes, in order to more clearly indicate their relationship to their corresponding P and I rows. So, the retrograde of P8 is R8, not R4; the retrograde row form that starts on F is R9; the retrograde of I3 is RI3, even if the row form does start on G.