Algorithmic Composition: A Guide to Composing Music with Nyquist

Chapter 4. Programming and Nyquist

43 Chapter 4 Programming and Nyquist In Chapter 3, we looked at data types (including numbers, symbols, and lists), expressions, and functions. In this chapter, we will learn how to write programs and make sounds. 4.1 Getting Started The normal way to write a program is to type code into a file. The file is then loaded into Nyquist. Loading means that the expressions in the file are evaluated. Usually, most of the expressions in a file define functions. Files are convenient because, if there is an error, you can simply edit the file and reload it rather than retyping everything. Using the jnyqide program, click on the New File button below the text input area. A new window will appear. Save the empty window to “simple.sal” so the editor will display the file using SAL syntax. Now, you can type a program into this window. Try typing the following text. Example 4.1.1: simple.sal ;; a simple program define function my-program() begin print "this is a test" play pluck(c4) end Note: examples labeled with a filename as in Example 4.1.1 are included in the accompanying electronic media. (See page 1.) This program begins with a comment. A comment is text that is not evaluated. Comments begin with a semicolon and extend to the end of the line. Sometimes, programmers use two or more semicolons to make comments stand out, but you could just as well write “; hey you! – a simple program” as long as the first character is a semicolon. Use comments to describe your programs, intentions, and details that you might forget when you (and others) read the program . Following the comment is a function definition. The print command prints a line of text to the Nyquist output to confirm that 44 Chapter 4 ⋅ Programming and Nyquist the function has been called. The pluck function generates a plucked string sound, and play plays the sound as audio. For now, do not worry about how pluck and play work because we just want to create and run any Nyquist program using files. Notice that my-program has two commands (print and play). When a function definition has multiple expressions, they are evaluated sequentially. Figure 4.1.1: The Nyquist IDE (Macintosh version) The screen should look something like Figure 4.1.1. When the program is ready, click on the Load button. Nyquist will then load the file and generate output similar to the following: Example 4.1.2: Output from loading simple.sal SAL> exec setdir("/Users/rbd/temp") SAL> load "/Users/rbd/temp/simple.sal" SAL> Notice that you do not need to type anything to the text area. Instead , jnyqide automatically types a command to set Nyquist’s current directory to wherever you saved the file and then a command to load the file. 4.1 Getting Started 45 After the file is loaded, my-program will be defined and available for use. To evaluate an expression (such as a function call), use the command exec as shown in Example 4.1.3. Example 4.1.3: Using exec to call a function SAL> exec my-program() this is a test Saving sound file to temp.wav total samples: 44100 AutoNorm: peak was 1.24552, peak after normalization was 0.9, suggested normalization factor is 0.722587 SAL> The print command in my-program generates the output line “this is a test”. Next, the pluck sound is generated and played by the play function. Some information is printed by play. First, play normally saves a copy of the sound to a file, in this case “temp.wav.” (You can replay the sound from this file by clicking on the Replay button in jnyqide.) Next, play tells us that it performed 44100 samples of audio. The line beginning with “Autonorm” tells us the peak audio level of the original sound was 1.24552. Normally, audio samples should be in the range from −1 to +1. If necessary, Nyquist tries to adjust the output level to avoid clipping. As indicated in the printout, the sound was scaled to achieve a peak of 0.9. Based on the final outcome, the “suggested” normalization factor of 0.722587 is the value that one might use to scale the sound manually. If you run my-program again, these numbers will change because the pluck sound is initialized with random numbers and produces...