Using Envelopes

The body of a basic electronic kick drum is a sine wave with an exponential decrease in frequency over time. Depending on the taste, this drop happens from about 200-300 Hz to 30-60 Hz. This can be achieved with temporal envelopes.

Define Envelopes

Before using an envelope, it needs to be defined, using the Env class. It is feature rich and well documented insice the SC help files. The following line creates an exponential envelope with a single segment, defining an exponential drop. It can be plotted using the envelope's plot method:

~env = Env([1, 0.1], [0.15], \exp);
~env.plot;
/images/basics/sc-envelope.png

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Using an Envelope Generator

Envelopes can be passed to envelope generators. The following example generates a control rate signal with the exponential characteristics. It will be sent to the control bus with the index 0 (Out.kr(0,)) and the created node will be freed once the envelope is done, defined by the done action. The bus can be monitored to see the result:

s.scope(1,0,rate:'control')

{Out.kr(0,EnvGen.kr(~env, doneAction: Done.freeSelf))}.play

A "Kick" SynthDef

The following SynthDef uses the envelope inside the node. No bus is needed for The synth has two arguments - the gain and the pitch:

(
SynthDef(\kick,
{
    |gain=1,pitch=100|

    var env = EnvGen.kr(~env, doneAction: Done.freeSelf);

    // send the signal to the output bus '0'
    Out.ar(0, gain*SinOsc.ar(env*pitch));
};
).send(s)
)

Triggering it

The SynthDef can now be used to create a node on the server. It receives two arguments for gain and pitch:

Synth(\kick, [1,300])

Once the envelope is finished, the '''Done.freeSelf''' will remove the whole node from the server. When multiple envelopes are used within a node, the first one to finish will free the node, if set to '''doneAction: Done.freeSelf'''. Other doneActions can help prevent this ('''Done.none''').

Exercise