I'm trying to set a velocity value, a value that is in a midi signal to gain. The velocity ranges from 0 to 127.
The documentation on the web audio api albeit well done, doesn't really say anything about this.
At the moment I've this to play sounds :
play(key, startTime) {
this.audioContext.decodeAudioData(this.soundContainer[key], (buffer) => {
let source = this.audioContext.createBufferSource();
source.buffer = buffer;
source.connect(this.audioContext.destination);
source.start(startTime);
});
}
I didn't find anything to use the velocity values that range from 0 to 127. However I found gain node that applies a gain.
So my function is now this:
play(key:string, startTime, velocity) {
this.audioContext.decodeAudioData(this.soundContainer[key], (buffer) => {
let source = this.audioContext.createBufferSource();
source.buffer = buffer;
source.connect(this.gainNode);
this.gainNode.connect(this.audioContext.destination);
this.gainNode.gain.value = velocity;
source.start(startTime);
});
}
Eehhh... if I apply the midi velocity value to the gain, I obviously have a sound that is insanely loud. So I'd like to know either of those two questions:
- Can I somehow use the velocity value directly ?
- How can I convert the velocity value to gain ?
CL. :
The MIDI specification says:\n\n\n Interpretation of the Velocity byte is left up to the receiving instrument. Generally, the larger the numeric value of the message, the stronger the velocity-controlled effect. If velocity is applied to volume (output level) for instance, then higher Velocity values will generate louder notes. A value of 64 (40H) would correspond to a mezzo-forte note […] Preferably, application of velocity to volume should be an exponential function.\n\n\nThe General MIDI specifications are not any more concrete.\n\nThe DLS Level 1 specification says:\n\n\n The MIDI Note Velocity value is converted to attenuation in dB by the Concave Transform according to the following formula:\n \n attendB = 20 × log10(1272 / Velocity2)\n \n and fed to control either the volume or envelope generator peak level.\n\n\nYou then have to map this attenuation to the gain factor, i.e., gain = velocity² / 127².\n\nAnd many hardware synthesizers allow to select different curves to map the velocity to volume.",
2016-12-08T18:25:26