visualise the oscilloscope of each channel, while playing

[adrienjoly]

Inspiration:

• https://www.youtube.com/watch?v=KZAnUDAj94Y
• https://code.tutsplus.com/tutorials/how-to-create-an-audio-oscillator-with-web-audio-api--cms-29943

Suggested next steps:

• integrate @netgusto's oscilloscope visualization => PR First implementation of a scope viz #6 (merged)
• refactor: prevent the scope from being re-initialized for every note
• refactor: also prevent the audio context and oscillator from being re-initialized for every played note, if possible
• integrate a second scope viz for the sound generator (mapped to keys Q, W, E and R)
• allow more than 1 MIDI keyboard to be plugged and allocate a separate scope viz for it (i.e. one scope per instrument)

[adrienjoly]

In PR #6, @netgusto integrated an oscilloscope visualization with stabilization and connected it to the synth.

[adrienjoly]

@netgusto I just made the oscilloscope integration polyphonic! :-)

Whenever you have time, a good next step would be to plug a separate oscilloscope instance (and separate canvas) to sound-generator.js, so we can visualize drum sounds too ^^

Have a great weekend!