It is also possible to modify the duration and amplitude of a sample using an ADSR envelope. However, this works slightly differently to the ADSR envelope available on synths. Sample envelopes only allow you to reduce the amplitude and duration of a sample - and never to increase it. The sample will stop when either the sample has finished playing or the envelope has completed - whichever is first. So, if you use a very long release:, it won’t extend the duration of the sample.
Let’s return to our trusty friend the Amen Break:
sample :loop_amenWith no opts, we hear the full sample at full amplitude. If we want to fade this in over 1 second we can use the attack: param:
sample :loop_amen, attack: 1For a shorter fade in, choose a shorter attack value:
sample :loop_amen, attack: 0.3Where the ADSR envelope’s behaviour differs from the standard synth envelope is in the sustain value. In the standard synth envelope, the sustain defaulted to 0 unless you set it manually. With samples, the sustain value defaults to an automagical value - the time left to play the rest of the sample. This is why we hear the full sample when we pass no defaults. If the attack, decay, sustain and release values were all 0 we’d never hear a peep. Sonic Pi therefore calculates how long the sample is, deducts any attack, decay and release times and uses the result as your sustain time. If the attack, decay and release values add up to more than the duration of the sample, the sustain is simply set to 0.
To explore this, let’s consider our Amen break in more detail. If we ask Sonic Pi how long the sample is:
print sample_duration :loop_amenIt will print out 1.753310657596372 which is the length of the sample in seconds. Let’s just round that to 1.75 for convenience here. Now, if we set the release to 0.75, something surprising will happen:
sample :loop_amen, release: 0.75It will play the first second of the sample at full amplitude before then fading out over a period of 0.75 seconds. This is the auto sustain in action. By default, the release always works from the end of the sample. If our sample was 10.75 seconds long, it would play the first 10 seconds at full amplitude before fading out over 0.75s.
Remember: by default, release: fades out at the end of a sample.
We can use both attack: and release: together with the auto sustain behaviour to fade both in and out over the duration of the sample:
sample :loop_amen, attack: 0.75, release: 0.75As the full duration of the sample is 1.75s and our attack and release phases add up to 1.5s, the sustain is automatically set to 0.25s. This allows us to easily fade the sample in and out.
We can easily get back to our normal synth ADSR behaviour by manually setting sustain: to a value such as 0:
sample :loop_amen, sustain: 0, release: 0.75Now, our sample only plays for 0.75 seconds in total. With the default for attack: and decay: at 0, the sample jumps straight to full amplitude, sustains there for 0s then releases back down to 0 amplitude over the release period - 0.75s.
We can use this behaviour to good effect to turn longer sounding samples into shorter, more percussive versions. Consider the sample :drum_cymbal_open:
sample :drum_cymbal_openYou can hear the cymbal sound ringing out over a period of time. However, we can use our envelope to make it more percussive:
sample :drum_cymbal_open, attack: 0.01, sustain: 0, release: 0.1You can then emulate hitting the cymbal and then dampening it by increasing the sustain period:
sample :drum_cymbal_open, attack: 0.01, sustain: 0.3, release: 0.1Now go and have fun putting envelopes over the samples. Try changing the rate too for really interesting results.