A piece of weird music!

Question

As a new recruit of your favourite intelligence service, you are out enjoying a rare bit of time off at the theatres. You are laughing with the rest of the crowd when you feel a tap on your shoulder and hear the rustling of paper. You turn around. You see no one. Looking down you see a piece of paper. If you weren't in your current job, you would have just ignored this. But being a somewhat trained agent, you see that there's more to this than meets the eye. Do you have what it takes to find out what to do before you get fired, or even worse, fired at?

Hint 1

Everything except the image is flavour text, the title and author of the music are irrelevant.

Hint 2

What key is this "song" written in? Maybe it will help...

Hint 3

Try writing down each note...

Hint 4

Only the notes, lengths, ties and tempos are relevant...

Hint 5

Conventionally, a crotchet denotes one unit (or one beat in common time for you experts)...

Hint 6

Convert notes to numbers then apply some operations (addition/multiplication)...

Hint 7

There are SEVEN notes in an octave...

Hint 8:

Take the key from Hint 2 and let that be 0...

Hint 9:

Ties are to do with addition

Answer 1

The message is:

URGENT MEET BACKSTA E ASAP

If we

write down all the notes (like harlan) with their durations, and add brackets to denote legato, we get the following:

3D5 2E5 G4 5D5 G5 2F5 F4 F5 5D5 5D5 2F5
2F4 2C6 3F5 (1/2G5 1/2G5 1/2A5 1/2F5 1/2G5 1/2E5) D5 (F5 E5) 2F5 3F5 F4
(D5 C5 Bb4 A4 G4 A4 Bb4 D5) (1/4F4 1/4F4 1/4F4 1/4F4) 3F5 (D5 1/2F5 1/2A5) (E5 F5 G5) (D5 1/2D5 1/2D5 2F4)

Now we compute the value of the note by counting the number of notes that it is above F4 (so F4 is 0, G4 is 1, etc.), and multiply this by the length of the note. We also add the values of notes that are played legato. The following values are found this way:

15 12 1 25 8 14 0 7 25 25 14
0 22 21 23 5 13 14 21 0
25 0 21 13 21 10

Now converting each of these values to a letter (with A = 1, B = 2, etc.) and replace 0's by spaces, we get:
OLAYHN GYYN VUWEMNU Y UMUJ
This is encoded using a Caesar cipher with key 20, decoding yields:
URGENT MEET BACKSTA E ASAP
So I guess that the message is to meet someone with codename "Backsta E" as soon as possible (or I made a mistake somewhere).

Answer 2

I couldn't quite figure out what the musical notes meant, but I did find out how it sounds. Unfortunately, I'm a programmer, not a musician, so I couldn't play the music on the piano. The best I could do was to quickly write some Java code that could reproduce the music using MIDI:

import java.io.FileOutputStream;

import javax.sound.midi.MetaMessage;
import javax.sound.midi.MidiEvent;
import javax.sound.midi.MidiSystem;
import javax.sound.midi.Sequence;
import javax.sound.midi.Sequencer;
import javax.sound.midi.ShortMessage;
import javax.sound.midi.Track;

public class PuzzlingSound {

    enum Note {
        C, C_SHARP, D, D_SHARP, E, F, F_SHARP, G, G_SHARP, A, B_FLAT, B
    }

    public static void main(String[] args) throws Exception {
        Sequencer sequencer = MidiSystem.getSequencer();
        sequencer.open();
        Sequence seq = new Sequence(Sequence.PPQ, 4);
        Track t = seq.createTrack();

        //set tempo to 203
        t.add(new MidiEvent(new MetaMessage(0x51, new byte[] {0x04, (byte) 0x82, (byte) 0x8E}, 3), 0));

        //add notes to sequence
        addNote(t, Note.D, 5, 100, 1, 3);
        addNote(t, Note.E, 5, 100, 4, 1);
        addNote(t, Note.E, 5, 100, 5, 1);
        addNote(t, Note.G, 4, 100, 6, 1);
        addNote(t, Note.D, 5, 100, 7, 2);
        addNote(t, Note.D, 5, 100, 9, 3);
        addNote(t, Note.G, 5, 100, 12, 1);
        addNote(t, Note.F, 5, 100, 13, 2);
        addNote(t, Note.F, 4, 100, 15, 1);
        addNote(t, Note.F, 5, 100, 16, 1);
        addNote(t, Note.D, 5, 100, 17, 4);
        addNote(t, Note.D, 5, 100, 21, 1);
        addNote(t, Note.D, 5, 100, 22, 3);
        addNote(t, Note.D, 5, 100, 25, 2);
        addNote(t, Note.F, 5, 100, 27, 2);
        addNote(t, Note.F, 4, 100, 29, 2);
        addNote(t, Note.C, 6, 100, 31, 2);
        addNote(t, Note.F, 5, 100, 33, 3);
        addNote(t, Note.G, 5, 100, 36, 0.5);
        addNote(t, Note.G, 5, 100, 36.5, 0.5);
        addNote(t, Note.A, 5, 100, 37, 0.5);
        addNote(t, Note.F, 5, 100, 37.5, 0.5);
        addNote(t, Note.G, 5, 100, 38, 0.5);
        addNote(t, Note.E, 5, 100, 38.5, 0.5);
        addNote(t, Note.D, 5, 100, 39, 1);
        addNote(t, Note.F, 5, 100, 40, 1);
        addNote(t, Note.E, 5, 100, 41, 1);
        addNote(t, Note.F, 5, 100, 42, 2);
        addNote(t, Note.F, 5, 100, 44, 1);
        addNote(t, Note.F, 5, 100, 45, 2);
        addNote(t, Note.F, 4, 100, 47, 1);
        addNote(t, Note.D, 5, 100, 48, 1);
        addNote(t, Note.C, 5, 100, 49, 1);
        addNote(t, Note.B_FLAT, 4, 100, 50, 1);
        addNote(t, Note.A, 4, 100, 51, 1);
        addNote(t, Note.G, 4, 100, 52, 1);
        addNote(t, Note.A, 4, 100, 53, 1);
        addNote(t, Note.B_FLAT, 4, 100, 54, 1);
        addNote(t, Note.D, 5, 100, 55, 1);
        for(double i = 0; i < 1; i += 0.25)
            addNote(t, Note.F, 4, 100, 56 + i, 0.25);
        addNote(t, Note.F, 5, 100, 57, 3);
        addNote(t, Note.D, 5, 100, 60, 1);
        addNote(t, Note.F, 5, 100, 61, 0.5);
        addNote(t, Note.A, 5, 100, 61.5, 0.5);
        addNote(t, Note.E, 5, 100, 62, 1);
        addNote(t, Note.F, 5, 100, 63, 1);
        addNote(t, Note.G, 5, 100, 64, 1);
        addNote(t, Note.D, 5, 100, 65, 1);
        addNote(t, Note.D, 5, 100, 66, 0.5);
        addNote(t, Note.D, 5, 100, 66.5, 0.5);
        addNote(t, Note.F, 4, 100, 67, 2);

        MidiSystem.write(seq, 0, new FileOutputStream("C:\\Users\\redacted\\OneDrive\\Puzzling.mid"));

        //play sequence on computer
        sequencer.setSequence(seq);
        sequencer.start();
    }

    /**
     * Adds a note to the musical sequence.
     * @param t the musical track
     * @param note the note
     * @param octave the octave
     * @param velocity how fast the note is hit
     * @param when when to strike the note in the sequence
     * @param time how long to keep the note held
     * @throws Exception if an exception is thrown by code this calls
     */
    public static void addNote(Track t, Note note, int octave, int velocity, double when, double time) throws Exception {
        ShortMessage on = new ShortMessage();
        on.setMessage(ShortMessage.NOTE_ON, 1, getNote(note, octave), velocity);
        t.add(new MidiEvent(on, (int) (4 * when)));
        ShortMessage off = new ShortMessage();
        off.setMessage(ShortMessage.NOTE_OFF, 1, getNote(note, octave), velocity);
        t.add(new MidiEvent(off, (int) (4 * (when + time))));
    }

    /**
     * Returns MIDI note based on piano note and octave. Helper called by {@link #addNote}.
     * @param note the note
     * @param octave the octave (Middle C on octave 4)
     * @return the MIDI note
     * @throws IllegalArgumentException if octave is beyond piano range (-1 to 9)
     */
    public static int getNote(Note note, int octave) {
        if(octave < -1 || octave > 9)
            throw new IllegalArgumentException();
        return 12 * (octave + 1) + note.ordinal();
    }
}

This was the MIDI file that this code outputted.

Answer 3

Adding perhaps a step, but certainly not a full answer yet.

If we write out the pitches (& I'm putting in parentheses notes that if played would not be articulated--e.g. would tie across the bar--but I'm thinking are probably meant to be 'articulated' here), we get:

D5 E5 (E5) G4 D5 (D5) G5 F5 F4 F5 D5 (D5) D5 (D5) F5 F4 C6 F5 G5 G5 A5 F5 G5 E5 D5 F5 E5 F5 F5 (F5) F4 D5 C5 Bb4 A4 G4 A4 Bb4 D5 F4 F4 F4 F4 F5 D5 F5 A5 E5 F5 G5 D5 D5 D5 F4

The note lengths if combined with tempo to get duration make for some gnarly long numbers (e.g. 0.8866995073891626 sec to start) so I'm inclined to think their values as otherwise represented might be a better path to follow. The dotted half to start could be as 3 beats in the tempo, or 12 of the shortest duration used herein (16th notes), for instance.

Also, @gparyani, thanks for the midi, but some of the notes sound off pitch to me (I'm a musician and not (much of) a programmer). A couple of the F4s sounded like E4s in your midi, the last D5s sounded I think as Bb4s, and a couple others I can't recall. In case your programming route gets to the answer, might be helpful to tweak.