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Spigot Demo 1

This sporth patch is a simple demonstration of Spigot, a sporth plugin that is both a sequencer and interpretor for the pbrain language. This reads from a list of example pbrain strings, and will sonifies the eight core instructions.

Setup

Loading up the examples

A set of strings (read line-by-line in "examples.txt" ) are loaded into a string-list list via slist. slist statically allocates an array, so a reasonably large value of 10 is used (at present, there are only 3 example strings).

 _list 10 "examples.txt" slist

Loading the plugin

The spigot custom ugen is loaded up via fl. The assumption here is that the shared object file is in the current directory.

 _spigot "./spigot.so" fl

Tables and Variables

A number of tables and variables are initialized.

• The table notes creates a table of MIDI note numbers, one for each instruction. Since the instructions are not zero indexed, an extra value is appened at the beginning
• The variable val will be used to store the signal generated from spigot.
• The variable clk will store the clock signal.
• The variable env will store the envelope signal.

 _notes "60 60 62 64 67 69 71 72 74" gen_vals
 _val var
 _clk var
 _env var

Runtime

Clock

The clock signal is the first signal to be generated in the patch. It will control the speed of the spigot virtual CPU. The clock it set to tick once every 300ms via dmetro. This slow rate is done for do demonstration purposes, so it is easy to hear what instruction it is on.

 0.3 dmetro _clk set

Instantiating Spigot

An instance of Spigot is created via fe. The arguments that spigots take are an input signal (which spigot can optionally read), and the clock signal clk.

 # Input Signal
 0 
 # Clock Signal
 _clk get 

Spigot parses a string rather than a file. The string is selected from the slist list via sget.

 2 _list sget
 _spigot fe 

The output of spigot is the current instruction executed (if triggered), otherwise it is zero. This value is stored in the variable val.

 _val set

Envelope

Next, the envelope signal is generated via tenvx. Recall that a trigger in a clock signal is a sample that is non-zero. Because of this, val is able to be used as a clock signal

 _val get 0.001 0.01 0.01 tenvx 

The signal of the envelope is set to env.

 _env set

It is immediately retrieved for later. Probably should have used dup here.

 _env get 

Setting the Frequency

The frequency of the oscillator is determined by the output of spigot, so it is retrieved from val.

 _val get 

To better grok the instructions, the value is printed to the terminal.

 "val" print 

The signal is duplicated and turned into a specific trigger signal using the ne (not equals) operator. These two values feed a sample and hold generator samphold. This is needed because the output of spigot is essentially a trigger signal and not a step signal.

 dup 0 ne samphold 

The instructions correspond to indices in the table notes, which we access via tget. These are then converted to a frequency via mtof.

 _notes tget mtof 

Frequency is the first argument needed for the FM oscillator, which is used for sound generation.

The FM oscillator

Amplitude, and the carrier/modulator ratios are set. These are just constants. The C:M ratio is 1:7, a very common ratio used for FM tine piano sounds.

 0.3 1 7 

The modulation index uses the envelope stored in inv as a control parameter. This effectively modulations the brightness of the FM oscillator.

 _env get 1 * 

The FM oscillator is then multiplied by the envelope, which was pushed on the stack previously. This signal is then duplicated to make a stereo patch

 fm * dup

Closing

The sporth plugin is closed via fc. Not necessary, but the nice thing to do.

 _spigot fc

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