Playing Piano Midi Notes on an Original Espruino Board using the DAC

Playing Piano Midi Notes on an Espruino Original Board

Using the Espruino examples found here:

Espruino Waveforms

A recording of Middle C played on a piano was found here:

Piano C4 Sample

As per the example Audacity found here:
Audacity

was used to create an audio sample at 8 kHz rate in unsigned 8 bit format.

The function get_freq(note) was constructed so that the playback rate of the sound sample can be adjusted to change the pitch of the note. The note is specified as a Midi note number.
Middle C is Midi note number 60 (aka C4), C above middle C (aka C5) is midi note number 72.

function get_freq(note){ //note is midi note
note=note-60;
var octave=Math.log(2);
var halftone=octave/12;
//console.log(note);
var tone=Math.exp(note*halftone);
var freq=8000*tone; //C4 Middle C Midi note 60
return freq;
}// end get_freq

The sample was converted to a string and coded into the program

// 8 bit unsigned Piano C4 sampled at 8 kHz
Piano=
"\x7f\x80\x80\x7f\x80\x7f\x80\x80\x80\x7­f\x80\x7f\x80\x80\x80\x80\x80\x7f\x80\x7­f\x80\x7f\x80\x80\x80\x80\x80\x80\x7f\x8­0\x7f\x80\x7f\x80\x7
...
\x80\x80\x81\x80\x80\x81\x81\x81\x81\x80­\x81\x82\x82\x82\x82\x82\x81\x80\x7f~}||­|}}~~\x7f"
;

The chromatic scale is played by this code:

k=0;
var ww = new Waveform(Piano.length);//,{bits:16});
ww.buffer.set(Piano);

note=60;
analogWrite(A4, 0.5);
ww.startOutput(A4,get_freq(note));

// this event doesn't fire unless repeat is true
ww.on('buffer',function(data) { 
  console.log("B");
  k++;
  if (k>3) ww.stop();
 });


ww.on('finish',function(data) { console.log("F");//+data);
note++;
k=0;
if (note>72) note=60;//{
ww.startOutput(Aout, get_freq(note));//,{repeat:true});
//}
 });

Discussion

Other instrument samples are widely available on the Web. (Orchestras)
The tempo of the notes increases with pitch. How to solve this?
With only 2 DACs, polyphony is limited. Using PWM can produce synthesized sounds.

attached files

Piano1 .js

1 Attachment

• piano1.js