Something That Rings a Bell

This article is part of the Aerodynamic guide.

We are now going to focus on the first part of the track: bell, that is, the 4 strokes of the bell at the beginning of the track ; here is what it looks like once imported in Sonic Visualizer:

This is a spectrogram, in abscissa we have time and in ordinate we have audio frequencies. We can see 4 distinct areas, one for each stroke. We also see horizontal stripes at different pitches: it corresponds to the audio frequencies of the bell sound, the more they tend to be red, the more intense the frequencies are. A musical instrument generally plays a note which is represented by the most intense frequency stripe, the other stripes are the timbre of an instrument: each instrument has its own signature which can be more or less elaborated (for instance, the timbre of a flute is much simpler than a violin’s one). Here, the most intense stripe is at 220 Hz (at the bottom of the image), that is, the note :A3.

A simple version of these 4 bell strokes can be expressed this way in Sonic Pi:

use_bpm 123
use_synth :pretty_bell

4.times do
    play :A3
    sleep 8
end

Which means:

When we execute this code (the Run button), we hear a bell stroke every 8 beats, 4 times.

First problem, the duration of the bell sound isn’t the one we are looking for (it is much shorter than in Aerodynamic). The instruments of Sonic Pi can be tweaked with parameters, some of them manipulate the duration of notes.

If we give another look at the previous spectrogram, we see that the intensity of each frequency decreases with time: the active frequencies are at first red (high intensity), then they progressively become green (low intensity). Moreover, after 8 beats, they are still slightly active, as if they were actually on 9 beats. These two charactetistics of the note can be obtained with the release parameter, which increases the duration of a note, and progressively decreases its intensity :

use_synth :pretty_bell
use_synth_defaults release: 9

4.times do
    play :A3
    sleep 8
end

We are now closer to Aerodynamic! But that’s still not very convincing because the timbre of the bell from Sonic Pi isn’t the same as the one we are looking for. In other terms, the horizontal stripes produced by Sonic Pi’s bell, despite being based on the note A3, are different. Here’s what it looks like in Sonic Visualizer:

At the top, we have the bell from Aerodynamic ; at the bottom our version: indeed, we are quite far from it, we are missing a lot of timbre! We can try to fix this by playing several bells at the same time, with reduced amplitude on octaves around A3, so as to cover a larger part of the spectrum:

use_bpm 123

use_synth :pretty_bell
use_synth_defaults release: 9

4.times do
    play :A1, amp: 0.125
    play :A2, amp: 0.25
    play :A3, amp: 0.75
    play :A4, amp: 0.40
    play :A5, amp: 0.25
    sleep 8
end

When we call several times play in a row, it plays everything in parallel, this is the call to sleep which introduces the pause, therefore we have here 4 iterations on:

This fills some gaps in the spectrogram, it is still far from the original bell but it is satisfactory.

Finally, we can add some depth and distance with the help of the gverb effect, which we apply around the play instructions:

use_bpm 123

use_synth :pretty_bell
use_synth_defaults release: 9

4.times do
    with_fx :gverb, room: 20 do
        play :A1, amp: 0.25
    	play :A2, amp: 0.5
        play :A3, amp: 1.5
        play :A4, amp: 0.75
        play :A5, amp: 0.5
 	sleep 8
    end
end

The gverb effect applies to the block it wraps, we use it here with the room parameter set to 20 (its default value is 10), to increase the distance effect.

Sonic Pi has a collection of audio effects (whose number increases with each new release), it is possible to browse this collection via the help at the bottom of Sonic Pi, inside the Fx pane ; each effect has its own documentation, with the different possible parameters:

Next…

This article is part of the Aerodynamic guide.