I assume that this question arises because you're composing on a fixed-pitch instrument, tuned in 12-tone equal temperament, without distinction between enharmonic notes. Probably a piano.
For convenience, I shall denote the 12 notes of the chromatic scale with the integers modulo 12, using the convention that 0=C, 2=D, 4=E, 5=F, 7=G, 9=A, and 11=B; with 1, 3, 6, 8, and 10 being black keys.
The E (natural) minor scale consists of the notes E (4), F♯ (6), G (7), A (9), B (11), C (0), and D (2). Your bassline includes note 10 and you need to decide whether to notate it as A♯ or B♭ (or maybe even C𝄫).
Or more generally, how to denote the 5 chromatic notes that are not part of the diatonic E-minor scale.
- Is note 1 C♯, D♭, or B𝄪?
- Is note 3 D♯, E♭, or F𝄫?
- Is note 5 E♯, F, or G𝄫?
- Is note 8 G♯ or A♭?
- Is note 10 A♯, B♭, or C𝄫?
Approach #1: Match the key signature
You already have a sharp in your diatonic scale, so just use sharps for the 5 chromatic notes: C♯, D♯, E♯, G♯, and A♯.
For note 5, you could choose to use F instead of E♯, but since you'd have to write an accidental (♮) anyway to unsharpen the F♯, there's no notational advantage in doing so.
Approach #2: Tertian harmony
The popular types of chords in Western music are all built out of thirds: M3 (4 semitones) and m3 (3 semitones). There are 3 possible ways to reach note 10 from the E-minor scale and thirds:
- F♯ (6) + M3 (4) = A♯ (10)
- G (7) + m3 (3) = B♭ (10)
- D (2) - M3 (4) = B♭ (10)
So if, for example, you intend this note to be the middle of a F♯-major chord (F♯ + A♯ + C♯), spell it as A♯. If, OTOH, it's part of a G-minor chord (G + B♭
+ D), spell it as B♭.
Approach #3: Circle of Fifths
Assume that notes closer together on the Circle of Fifths are more consonant or otherwise “better” when played together. (For now, let's not debate whether this is actually true.)
The Circle of Fifths order of notes, with the E-minor scale in brackets, is:
For note names as close to the bracket diatonic scale as possible:
- Note 1 = C♯, only 1 fifth outside the scale (vs. D♭ which is 5)
- Note 5 = F♮, also only 1 fifth outside the scale (vs. E♯ which is 5)
- Note 8 = G♯, 2 fifths outside the scale (vs. A♭ which is 4)
- Note 10 = B♭, 2 fifths outside the scale (vs. A♯ which is 4)
- Note 3 is a tie between D♯ and E♭, each 3 fifths outside the scale. Break the tie by noting that it's far more common to raise the seventh note in a minor scale (as in harmonic and melodic minor) than the lower the first. So D♯.
The full E-minor chromatic scale in order is thus:
E, F♮, F♯, G, G♯, A, B♭, B, C, C♯, D, D♯, E
Or, using moveable-do solfège with the la-based (relative) minor convention:
la, ti♭ (te), ti, do, do♯ (di), re, mi♭ (me), mi, fa, fa♯ (fi), sol, sol♯ (si), la