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Note that in the context of Mini Micro, *waveform* refers to just *one* cycle of the air pressure changes, which is repeated many times per second. In other contexts, people may use "waveform" to refer to a graph of the entire sound, from beginning to end. |
So to define a simple sound, we need to know: |
1. What the waveform looks like. |
2. How many times per second that waveform should be repeated (i.e. the frequency). |
3. How long the sound should last. |
4. How the volume should change over the course of the sound. |
That third one, how long the sound should last, is called the *duration* of the sound; and that last one is called the *envelope*. |
envelope |
: how the amplitude (volume) of a sound varies from the beginning to the end of the sound |
And now you have all the background you need to understand sound synthesis in Mini Micro. The `Sound` class has some additional properties that correspond to the concepts above. |
{caption:"Properties and methods related to synthesizing sounds from scratch.", colWidths:"120,*"} |
|`snd.duration`|length of the sound, in seconds| |
|`snd.freq`|frequency (repeats of `waveform` per second)| |
|`snd.envelope`|how the sound amplitude varies over the course of the sound| |
|`snd.fadeIn`|length of fade-in period when sound begins, in seconds| |
|`snd.fadeOut`|length of fade-out period when sound begins, in seconds| |
|`snd.init` *duration, freq, envelope, waveform*|shortcut for setting the four key properties| |
|`snd.mix` *sound2, level|add another synthesized sound into this one| |
Let's begin, as usual, by experimenting on the REPL command line. |
```terminal |
]s = new Sound |
]s.duration = 1 |
]s.freq = 440 |
]s.envelope = 1 |
]s.waveform = Sound.sineWave |
]s.play |
``` |
You should hear a clean, pure note (for the musically inclined, this is A above middle C) that lasts for 1 second. Let's go over each of these properties in turn. |
First, `duration`. This one is easy enough: it's how long the sound lasts, in seconds. Try changing it and hear the difference. |
```terminal |
]s.duration = 1.5 |
]s.play |
]s.duration = 0.5 |
]s.play |
``` |
Next, frequency. You probably have a good idea of this by now, but go ahead and play with it a bit to be sure. |
```terminal |
]s.freq = 220 |
]s.play |
]s.freq = 880 |
]s.play |
``` |
However, you aren't limited to a single, constant frequency for the whole sound. If you give Mini Micro a list of frequencies, it will smoothly interpolate between them. Try these: |
```terminal |
]s.duration = 2 |
]s.freq = [220, 880] |
]s.play |
]s.freq = [880, 220] |
]s.play |
]s.freq = [220,300] * 8 |
]s.play |
``` |
That last one is using list replication; go ahead and print out `s.freq` to make sure you understood that correctly. And you can hear what it does to the sound: the pitch varies between 220 and 300 Hz, 8 times over the 2-second duration of the sound. |
Envelope is a little trickier. Here, Mini Micro is expecting either 1, which indicates a constant amplitude for the sound; or a list of values between 0 and 1, which indicate how the amplitude should vary over the course of the sound. For example, if you use an envelope of `[0,1]`, then the sound will start at an amp... |
```terminal |
]s.freq = 440 |
]s.envelope = [0,1] |
]s.play |
]s.envelope = [1,0] |
]s.play |
]s.envelope = [0,1,0] |
]s.play |
]s.envelope = [1,0,1] |
]s.play |
``` |
You can use as many values in your `envelope` list as you like; the synthesizer will evenly space these amplitude changes over the length of the sound. And of course you don't have to stick to only values of 0 and 1; you can use any values in between. For example, using list replication again: |
```terminal |
]s.envelope = [1, 0.25] * 8 |
]s.play |
``` |
It should be noted that the envelope isn't the *only* factor that affects the amplitude of the sound over time; there are also `fadeIn` and `fadeOut` properties. These are a simple way to make the sound fade in (go from zero to full amplitude) at the start of the sound, and fade out (go from full amplitude down to zer... |
Finally, let's consider the waveform. In the examples so far we've been using a sine wave, which is a pure, smooth variation in air pressure over time. Such a smooth waveform strongly excites only one of the frequency detectors in your ear, producing a sound that is clean and pure (and so rather boring). |
You can specify a waveform as a list of values from -1 to 1, and Mini Micro will interpolate over that list for each cycle of the sound. But the `Sound` class also has five common waveforms built right in, as shown below. |
{width:"97%"} |
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